A Complete Guide to Valves

What are valves?

In fluid piping systems, valves are control elements whose main functions are to isolate equipment and piping systems, regulate flow, prevent backflow, and regulate and discharge pressure. They can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, slurries, oils, liquid metals, and radioactive media. As it becomes very important to select the most suitable valve for the piping system, it becomes vital to understand the characteristics of the valve and the steps and basis for selecting the valve.

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20220726090346 40632 - A Complete Guide to Valves

Classification of valves

How to classify the valve?

First, the valve, in general, can be divided into two categories:

  • The first type of automatic valve: rely on the medium (liquid, gas) itself and the ability to act on its own valve.
  • Such as check valves, safety valves, control valves, traps, pressure reducing valves, etc.   
  • The second type of drive valve: with the help of manual, electric, hydraulic, or pneumatic to manipulate the action of the valve.

Such as gate valves, globe valves, throttle valves, butterfly valves, ball valves, plug valves, etc. 
Second, according to the structural characteristics of the classification, the direction of movement of the closing member relative to the valve seat can be divided into:

  • 1. Cut-off door-shaped: the closing member moves along the center of the valve seat.  
  • 2. Gate shape: the closing member moves along the center of the vertical valve seat.  
  • 3. Plug and ball: the closing member is a plunger or ball, rotating around its own centerline.  
  • 4. Spin-on shape: the closing member rotates around an axis outside the valve seat.  
  • 5. disc-shaped: the closing member is a disc, rotating around a shaft inside the valve seat.  
  • 6. Sliding valve shape: the closing member slides in the direction perpendicular to the channel. 

Third, according to the classification of use, the different uses of the valve can be divided into:  

  • 1. Open and closed: used to connect or cut off the pipeline medium, such as globe valves, gate valves, ball valves, butterfly valves, etc.  
  • 2. Check: used to prevent the backflow of media, such as check valves.  
  • 3. Adjustment: used to adjust the pressure and flow of the medium, such as regulating valves, and pressure reducing valves.  
  • 4. Distribution: used to change the direction of media flow, distribution of media, such as a three-way plug, distribution valve, slide valve, etc.   
  • 5. Safety valve: in the media pressure exceeds the specified value, used to discharge excess media to ensure the safety of piping systems and equipment, such as safety valves, and accident valves.
  • 6. Other special purposes: such as traps, air release valves, drain valves, etc. 

Fourth, according to the drive mode classification, the different drive modes can be divided into:  

  • 1. Manual: with the help of handwheels, handles, levers or sprockets, etc., with human drive, the transmission of larger torque is equipped with worm gears, gears, and other reduction devices.  
  • 2. Electric: With the help of electric motors or other electrical devices to drive.  
  • 3. Hydraulic: with the help of (water, and oil) to drive.  
  • 4. Pneumatic: driven by compressed air.

Five. Classification by pressure, according to the nominal pressure of the valve can be divided into:

  • 1. Vacuum valve: absolute pressure <0.1Mpa, i.e. 760mm Hg high valve, usually expressed in mm Hg or mm water column pressure.  
  • 2. Low-pressure valve: nominal pressure PN ≤ 1.6Mpa valve (including PN ≤ 1.6MPa steel valve)  
  • 3. Medium pressure valve: nominal pressure PN2.5-6.4MPa valve.  
  • 4. High-pressure valve: nominal pressure PN10.0-80.0MPa valve.  
  • 5. Ultra-high pressure valve: nominal pressure PN ≥ 100.0MPa valve. 

Six, according to the temperature classification of the medium, the temperature of the medium when the valve works can be divided into.  

  • 1. Ordinary valves: valves for the medium temperature -40 ℃ -425 ℃.  
  • 2. High-temperature valves: applicable to the medium temperature 425 ℃ -600 ℃ valve.  
  • 3. Heat-resistant valves: applicable to the medium temperature of 600 ℃ or more valves.  
  • 4. Low-temperature valves: applicable to the medium temperature -150 ℃ -40 ℃ valve.  
  • 5. Ultra-low temperature valves: applicable to the medium temperature -150 ℃ below the valve. 

Seven, according to the nominal diameter classification, according to the nominal diameter of the valve can be divided into. 

  • 1. Small-diameter valves: nominal diameter DN < 40mm valves.  
  • 2. Medium diameter valves: nominal diameter DN50-300mm valves.  
  • 3. Large diameter valves: nominal diameter DN350-1200mm valves.  
  • 4. Extra large diameter valves: nominal diameter DN ≥ 1400mm valves. 

Eight, according to the way of connection with the pipeline classification, according to the valve and the pipeline connection can be divided into  

  • 1. Flange connection valve: valve body with a flange, and the pipeline using flange connection valve.  
  • 2. Threaded connection valve: valve body with internal or external threads, and the pipeline using a threaded connection of the valve.  
  • 3. Welded connection valve: the valve body with a welded mouth, and the pipeline using a welded connection valve.  
  • 4. Clamp connection valve: the valve body with a clamp port, and the pipeline using a clamp connection valve.  
  • 5. Ferrule connection valves: valves connected to the pipeline using a ferrule.

Types of Commonly Used Valves

There are many types of valves and complex varieties, mainly gate valves, globe valves, throttle valves, butterfly valves, plug valves, ball valves, electric valves, diaphragm valves, check valves, safety valves, pressure reducing valves, steam traps, and emergency shut-off valves, etc. Among them, the commonly used are gate valves, globe valves, throttle valves, plug valves, butterfly valves, ball valves, check valves, and diaphragm valves.
IGate Valves
A gate valve also called a gate valve, is a widely used valve. Its closing principle is the gate sealing surface and the seat sealing surface are highly polished, flat, and consistent, fit each other, can stop the media flow through, and rely on the top mold, spring, or gate mold shape, to enhance the sealing effect. It mainly plays a cut-off role in the pipeline.
II. Shut-off valve
Globe valve, also called a cut-off valve, is the most widely used kind of valve, it is popular because the friction between the sealing surface during opening and closing is small, more durable, opening height is not large, easy to manufacture, easy to maintain, not only for low and medium pressure but also for high pressure.
Its closing principle is to rely on the pressure of the valve bar, so that the sealing surface of the valve flap and the sealing surface of the valve seat closely fit, to stop the flow of media.
The globe valve only allows the medium to flow in one direction and is installed with directionality. Its structure length is greater than the gate valve, while the fluid resistance, long-term operation, and sealing reliability is not strong.
Globe valves are divided into three categories: straight-through, right-angle, and DC-type inclined globe valves.
III. Butterfly valve
A butterfly valve is also called a butterfly valve, as the name implies, its key components like a butterfly to the wind, and free gyration.
The butterfly valve’s flap is a disc that rotates around an axis inside the valve seat, and the size of the rotation angle is the opening and closing degree of the valve.
The butterfly valve has the characteristics of lightweight, saving materials than other valves, simple structure, rapid opening and closing, cutting off and throttling can be used, fluid resistance is small, and the operation of labor-saving. The butterfly valve can be made into a large diameter. Where butterfly valves can be used, it is best not to make gate valves, because butterfly valves are more economical than gate valves, and the adjustability is good. At present, the butterfly valve is widely used in hot water pipelines.
IV. Ball valve
The working principle of the ball valve is to make the valve open or closed by rotating the valve love. Ball valve switch light, small size, can be made into a large diameter, reliable sealing, simple structure, easy maintenance, sealing surface, and the spherical surface is often in a closed state, not easy to be eroded by the media, widely used in various industries.
Ball valves are divided into two categories, one is the floating ball type, and the second is the fixed ball type.
V. Plug valve
The plug valve is dependent on the rotation of the plug body around the centerline of the valve body to open and close the purpose. Its role is to cut off, divide the field and change the direction of media flow. Simple structure, small size, the operation only needs to rotate 90 degrees, fluid resistance is also not large. The disadvantage is that the switch is laborious, the sealing surface is easy to wear, easy to jam when high temperature, and not suitable for regulating the flow.
Plug valve, also known as rotary plug, cork, rotary heart door. It has many types, straight-through, three-way, and four-way.
VI. Check valve
Check valve is to rely on the force of the fluid itself automatically open and close the valve, its role is to stop the backflow of media. It has many names, such as check valve, one-way valve, single-flow gate, etc. The structure can be divided into two categories.

  • (1) Lifting type: the valve flap along the valve body vertical centerline movement. There are two types of check valves: one is horizontal, installed in the horizontal pipeline, the body shape is similar to the globe valve, and the other is vertical, installed in the vertical pipeline.
  • (2) Swing type: the valve flap rotates around the pin outside the seat, this type of valve has a single, double, and multi-flap, but the principle is the same.

The water pump suction pipe suction bottom valve is a deformation of the check valve, its structure is the same as the above two types of check valve, but its lower end is open, so that water can enter.
VII. Pressure-reducing valve
A pressure-reducing valve is an automatic valve to reduce the pressure of the medium to a certain value, generally, the pressure after the valve is less than 50% of the pressure before the valve. There are many kinds of pressure-reducing valves, mainly piston type and spring film type.
The piston type pressure reducing valve is a valve that reduces pressure by the action of a piston. A spring-loaded pressure-reducing valve relies on a spring and membrane for pressure balance.
VIII. Trap
The trap is also called steam drain valve, steam valve, water trap, water return box, water return door, etc. Its function is to automatically drain the trap. Its function is to automatically discharge the condensate that is continuously generated, and not to allow steam to come out.
A trap must be able to “identify” steam and condensate to function as a steam drainage valve. “Recognition” of steam and condensate is based on three principles: density difference, temperature difference, and phase change. Thus, three types of traps are manufactured based on these three principles: mechanical, thermostatic, and thermodynamic.
IX. Safety Valves
The safety valve is a safety device to prevent the bursting of pressure equipment and vessels or easily caused pressure rise or pressure inside the vessel exceeding the limit. Safety valves are pressure vessels, boilers, pressure piping, and other pressure systems that are widely used as safety devices to ensure the safe operation of the pressure system.
When the vessel pressure exceeds the design provisions, the safety valve automatically opens, and the discharge of gas reduces the excessive-high pressure inside the vessel to prevent damage to the vessel or pipeline. And when the pressure in the container is down to the normal operating pressure, that is, automatically close to avoid the container overpressure to discharge all the gas, thus causing waste and production interruption.
The safety valve is mainly composed of three parts: valve seat, valve flap (spool), and loading mechanism. The valve seat and the valve body is a whole, some are assembled with the valve body, which is connected to the equipment. The valve flap is often attached to a valve stem, which is fastened to the seat. Above the valve flap is the loading mechanism, and the size of the load can be adjusted. When the pressure in the equipment is within a certain range of working pressure, the internal medium acting on the valve flap above the force is less than the loading mechanism on the valve above the force, the difference between the two constitutes the sealing force between the valve flap and the valve seat so that the valve flap tightly pressed against the valve seat, the equipment can not discharge the medium.
When the pressure inside the equipment exceeds the specified working pressure and reaches the opening pressure of the safety valve, the internal medium acting on the top of the flap is greater than the force exerted on it by the loading mechanism, so the flap leaves the valve seat, the safety valve opens, the medium inside the equipment is discharged through the valve seat, if the discharge volume of the safety valve is greater than the safety discharge volume of the equipment, the pressure inside the equipment is gradually falling, and through a short period of exhaust, the pressure is reduced back to normal working pressure.
At this time, the internal pressure acting on the valve flap above the force is less than the force applied to it by the loading mechanism, the valve flap and pressed against the valve seat, the media stopped discharging, and the equipment maintains normal working pressure continue to run. Therefore, the safety valve is through the media force on the valve flap and the loading mechanism of the force of the elongation, self-closing, or opening to prevent equipment overpressure purposes.
At present, the mass production of safety valves is spring and rod types two categories. There are also impulse-type safety valves, pilot-operated safety valves, safety switching valves, safety relief valves, static weight safety valves, etc. Spring type safety valve mainly relies on the force of the spring and work, spring type safety valve and closed and unclosed, generally flammable, explosive or toxic media should be selected closed, steam or inert gas, etc. can choose not closed, in the spring type safety valve with a wrench and without a wrench. The role of the wrench is mainly to check the degree of flexibility of the valve flap, which sometimes can also be used as a manual emergency pressure relief.
Lever type safety valve mainly relies on the force of the lever weight and work, but because of the large size of the lever type safety valve often limits the scope of choice. When the temperature is high, choose the safety valve with a radiator. The main parameter of the safety valve is the displacement, which is determined by the diameter of the valve seat and the opening height of the valve flap, which is different from the opening height and is divided into two types micro-open and fully open. Micro-opening refers to the opening height of the valve flap for the seat throat diameter of 1/40-l/20. full-opening refers to the opening height of the valve flap for the seat throat diameter of 1/4.
X. Regulating valve
Control valves are used to regulate the flow, pressure, and level of the medium. According to the signal of the regulating part, automatically control the opening of the valve, to achieve the adjustment of the medium flow, pressure, and liquid level. Control valves are divided into electric control valves, pneumatic control valves, and hydraulic control valves.
The control valve consists of two parts: electric or pneumatic actuator and a control valve. The control valve is usually divided into a straight single-seat control valve and a straight double-seat control valve, the latter has a large flow capacity, small unbalance office, and stable operation, so it is usually particularly suitable for large flow, high-pressure drop, and leakage fewer occasions.
Control valves can be divided into straight strokes and angle strokes according to the characteristics of the stroke. Straight stroke includes: single-seat valve, double-seat valve, sleeve valve, cage valve, angle valve, three-way valve, diaphragm valve; Angle stroke includes: butterfly valve, ball valve, eccentric rotary valve, full-featured ultra-lightweight control valve.
Control valves can be divided according to the driving mode: manual control valves, pneumatic control valves, electric control valves, and liquid control valves, that is, pneumatic control valves with compressed air as the power source, electric control valves with electricity as the power source, liquid medium (such as oil, etc.) pressure as the power of the liquid control valves.
The form of regulation can be divided into regulating type, cut-off type, and regulating cut-off type.
The flow characteristics can be divided into linear, logarithmic type (percentage), parabolic, and fast-opening.
XI. Diaphragm valve
Diaphragm valve with corrosion-resistant lined body and corrosion-resistant diaphragm instead of the spool assembly, the use of diaphragm movement to regulate the role. Diaphragm valve body material using cast iron, cast steel, or cast stainless steel, and lined with a variety of corrosion-resistant or wear-resistant materials, diaphragm material rubber, and polytetrafluoroethylene. The lined diaphragm is highly resistant to corrosion and is suitable for the regulation of strong acids, strong alkalis, and other strong corrosive media.
A diaphragm valve has a simple structure, low fluid resistance, and flow capacity is larger than other types of valves of the same specification; no leakage can be used for high viscosity and the regulation of media with suspended particles. The diaphragm isolates the medium from the upper chamber of the valve stem, so there is no packing medium that will not leak. However, due to the limitations of the diaphragm and lining materials, pressure resistance, and temperature resistance is poor, generally only for 1.6MPa nominal pressure and 150 ℃ or less.
Diaphragm valve flow characteristics are close to the fast-opening characteristics, in 60% of the stroke before the approximate linear, after 60% of the flow does not change significantly. Pneumatic form of diaphragm valves can also be equipped with feedback signals, limiters, positioners, and other devices to adapt to the needs of self-control, program control, or regulation of flow. Pneumatic diaphragm valve feedback signal using non-contact sensing technology.
The product uses a film-type propulsion cylinder, instead of a piston cylinder, excluding the piston ring is easy to damage, resulting in leakage and can not push the valve open and close the drawbacks. When the air source fails, you can still operate the hand wheel to open and close the valve.
Commonly used diaphragm valves are rubber-lined diaphragm valves, fluorine-lined diaphragm valves, unlined diaphragm valves, and plastic diaphragm valves.
XII. Throttle valve
The throttle valve in addition to the valve and the valve structure is basically the same, the valve is a throttling part, different shapes have different characteristics, and the valve seat diameter should not be too large, because its opening height is small media flow rate increases, thereby accelerating the erosion of the valve. The throttle valve is small in size, lightweight, good adjustment performance, but the adjustment accuracy is not high.

Characteristics of the valve

There are two general characteristics of the valve, use characteristics and structural characteristics.

20220726091836 75781 - A Complete Guide to Valves
Use characteristics: it determines the main performance and use of the valve, belonging to the valve use characteristics are: the type of valve (closed circuit valves, regulating valves, safety valves, etc.); product type (gate valve, globe valve, butterfly valve, ball valve, etc.); valve main parts (valve body, bonnet, stem, valve flap, sealing surface) materials; valve transmission mode, etc…
Structural characteristics: it determines the valve installation, repair, maintenance, and other methods of some structural characteristics, belonging to the structural characteristics are: the structure of the valve length and overall height, the form of connection with the pipeline (flange connection, threaded connection, clamp connection, external thread connection, welded end connection, etc.); the form of sealing surface (inlay ring, threaded ring, weld, spray welding, valve body); stem structure form (rotary rod, lift (rotating rod, lifting rod), etc.

Valve connection method

20220726093121 31641 - A Complete Guide to Valves

Flange connection

This is the most used connection form in the valve. The shape of the bonding surface can be further divided into the following types.

  1. Smooth type: Used for valves with low pressure. Processing is more convenient
  2. Convex: higher working pressure, can use the hard gasket
  3. Tongue and groove: available plastic deformation of the gasket, more widely used in corrosive media, the sealing effect is better.
  4. Trapezoidal groove type: oval metal ring for the gasket, used in the working pressure ≥ 64 kg / cm2 valve, or high-temperature valve.
  5. Lens type: gasket is lens-shaped, and made of metal. Used for working pressure ≥ 100 kg / cm2 of high-pressure valves, or high-temperature valves.
  6. O-ring type: This is a newer form of flange connection, which was developed with the emergence of a variety of rubber O-rings, it is in the form of sealing effect connection.

Clamping connection

Bolt directly to the valve and the two ends of the pipe wear clamped together in the form of connection.
Butt-welding connection
A connection is directly welded to the pipe.

Threaded connection

This is a simple connection method, often used for small valves. It is further divided into two cases.

  1. Direct sealing: The internal and external threads act directly as a seal. To ensure that the connection does not leak, it is often filled with lead oil, thread hemp, and PTFE raw material tape; among them, PTFE raw material tape, which is widely used day by day; this material has good corrosion resistance, excellent sealing effect, easy to use and save, and when disassembled, it can be removed intact, because it is a non-stick film, which is much superior to lead oil and thread hemp.
  2. Indirect sealing: The force of thread screwing is transferred to the gasket between the two planes, allowing the gasket to act as a seal.

Ferrule connection

Ferrule connection, its connection, and sealing principle are that when tightening the nut, the ferrule is under pressure, so that its edge bite into the outer wall of the tube, the outer cone of the ferrule, and under pressure and the cone of the joint body, and thus can reliably prevent leakage.
The advantages of this connection form are:

  1. Small size, lightweight, simple structure, easy disassembly, and assembly.
  2. Strong connection force, and a wide range of use, can withstand high pressure (1000 kg / cm2), high temperature (650 ℃), and shock vibration.
  3. Can choose a variety of materials, suitable for anti-corrosion.
  4. Processing accuracy requirements are not high; easy to install at height.

The ferrule connection form has been adopted in some small diameter valve products in China.

Clamp connection

This is a quick connection method, which requires only two bolts and is suitable for low-pressure valves that are frequently disassembled.

Internal self-tightening connection

All of the above connection forms use external force to counteract the medium pressure and achieve sealing. The following is the form of connection that uses medium pressure for self-tightening. It is installed at the inner core of the seal ring, and the media side of a certain angle, the media pressure to the inner cone, and then to the seal ring, in a certain angle of the cone, resulting in two forces, one parallel to the centerline of the valve body outward, the other pressure to the inner wall of the valve body. This latter force is the self-tightening force. The greater the medium pressure, the greater the self-tightening force. So this connection form is suitable for high-pressure valves. It saves a lot of material and labor than flange connection but also needs a certain amount of pre-tightening force to use reliably when the pressure inside the valve is not high. Valves made using the self-tightening seal principle are generally high-pressure valves.
There are many other forms of valve connections, such as small valves that do not have to be removed, or welded together with the pipe; some non-metallic valves, using socket connections, and so on. Valve users should be treated according to the specific situation.

Related accessories

There are valves and fittings, which are used in the connection or control system of the pipeline. Both valves and fittings cannot exist independently and are complementary to each other. Valve fittings are carbon steel and stainless steel, and PVC, or other materials, commonly used in the first two, in recent years, with the improvement of people’s living standards, the demand for foodstuffs also came with a large demand. So led to the rapid development of food machinery, so the stainless steel sanitary valve fittings production industry is red-hot, people usually say valve fittings, more or stainless steel sanitary.

Material of the valve

Valves are usually composed of body, cover, disc (gate), seat, stem, hot plate, packing, and driving parts (handwheel, gearbox or pneumatic device, electric device, etc.).

We call the body, cover material for the shell material (also known as the main material), gate (disc), ball, seat, stem, seal seat often called internal parts, in addition to fasteners and so on. According to the main material classification, people are often divided into:

  • Non-metallic material valve: such as ceramic valve, glass valve, plastic valve.
  • Metal material valve: such as copper alloy valve, aluminum alloy valve, lead alloy valve, titanium alloy valve, Monel valve, cast iron valve, carbon steel valve, alloy steel valve, etc.
  • Metal body lining denier valve: such as lined lead valve, lined plastic valve, lined enamel valve.

We will focus on carbon steel valves and alloy steel valves in metal materials.

First, the main material of the valve

1. Temperature and pressure grade of valve material

ASTM A216 WCB working pressure (psi) 1psi=0.006895MPa

Temperature ° F

150LB

300LB

600LB

900LB

1500LB

2500LB

– 20 – 100

285

740

1480

2220

3705

6170

200

260

675

1350

2025

3375

5625

300

230

655

1315

1970

3280

5470

400

200

635

1270

1900

3170

5280

500

170

600

1200

1795

2995

4990

600

140

550

1095

1640

2735

4560

650

125

535

1075

1610

2685

4475

700

110

535

1065

1600

2665

4440

750

95

505

1010

1510

2520

4200

800

80

410

825

1235

2060

3430

850

65

270

535

905

1340

2230

Valve test pressure: according to ASME B16.34, the shell strength test pressure is 1.5 times the working pressure and rounded to the next 25PSI, the water seal test pressure is 1.1 times the working pressure, and the gas seal test pressure is 0.6Mpa.

2. Valve commonly used ASTM body material

ASTM casting

ASTM forgings

Corresponding to the Chinese brand

Applicable temperature range °C

Applicable medium

Carbon steel

A216 WCB

A105

20

– 29-427

Water, liquefied gas, steam, oil, natural gas

Low carbon steel

A352 LCB

A350 LF2

16Mn

– 46 – 343

Low-temperature medium

A352 LCC

A350 LF2

16Mn

– 46 – 343

Low-temperature medium

High-temperature alloy steel

A217 WC1

A182 F1

– 29-468

High-temperature medium

A217 WC6

A182 F11

15CrMo

– 29-593

High-temperature medium

A217 WC9

A182 F22

10Cr2Mo1

– 29-593

High-temperature medium

A217 C5

A182 F5

1Cr5Mo

– 29-593

Corrosive high-temperature medium

A217 C12

A182 F9

– 29-593

High sulfur-oxidizing medium

Martensitic stainless steel

A217 CA15

A182 F6a

1Cr13

– 29-371

The strength above 450°C is lower than 304 °C

Austenitic stainless steel (C≤0.08)

A351 CF8

A182 F304

0Cr18Ni9

– 196 – 537

Corrosive medium

A351 CF8M

A182 F316

0Cr18Ni12Mo2Ti

– 196 – 537

Corrosive medium

Ultra-low carbon austenitic stainless steel (C≤0.03)

A351 CF3

A182 F304L

00Cr18Ni10

– 196 – 427

Corrosive medium

A351 CF3M

A182 F316L

00Cr18Ni14Mo2

– 196 – 454

Corrosive medium

Special alloys

A351 CN7M

UNS N08020

(ALLOY 20)

– 29-149

Oxidizing media and various concentrations of sulfuric acid

Monel alloy M-30C

UNS N04400

MONEL 400

– 29-482

Hydrofluoric acid, seawater

Hastelloy H.B H.C

Resistant to hydrochloric acid, dilute sulfuric acid, phosphoric acid, formic acid, acetic acid

H.C resistant to nitric acid, mixed acid of nitric acid and sulfuric acid

INCONEL alloy

Hot lye and alkaline sulfide

Two, the valve inner material

1. Valve Trim: disc sealing face, valve seat sealing face, stem (pin shaft), upper sealing seat, and small parts in contact with the medium.

List of commonly used interior materials

The package number

Disc sealing surface

Valve seat sealing surface

The valve stem

The seal seat

1

ER410

ER410

1Cr13

2Cr13

8

ER410

EDCoCr-A

1Cr13

2Cr13

5

EDCoCr-A

EDCoCr-A

1Cr13

2Cr13

2

304

304

F304

F304

15

EDCoCr-A

EDCoCr-A

F304

F304

10

316

316

F316

F316

12

316

EDCoCr-A

F316

F316

16

EDCoCr-A

EDCoCr-A

F316

F316

9

MONEL

MONEL

MONEL K500

MONEL 400

20

HSCuZn-3

HSCuZn-3

HPb59-1

HPb59-1

2. Valve commonly used inner material and service temperature

Within a material

Use temperature °C

Within a material

The use of temperature

304, 316,

– 268 – 316

17-4PH

– 40 – 427

Bronze

– 273 – 232

Cobalt base alloy (STELLITE 6)

– 273 – 816

INCONEL Nickel alloy

– 240 – 649

Electroless nickel plating (ENP)

– 268 – 427

MONEL alloy MONEL

– 240 – – 482

Chrome plated

– 273 – 316

Hastelloy H.B.

– 198 – 371

Butyl rubber (NBR)

– 40 – 93

Hastelloy H.C.

– 198 – 538

Fluorine rubber (VITON)

– 23-204

Titanium alloy

– 29-316

Polytetrafluoroethylene (PTFE)

– 268 – 232

Nickel base alloy

– 198 – 316

NYLON (NYLON)

– 73 – 93

ALLOY 20 (ALLOY 20)

– 46 – 316

polyethylene

– 73 – 93

Model 416 stainless steel 40RC

– 29-427

neoprene

– 40 – 82

Type 440 stainless steel 60RC

– 29-427

3. Valve commonly used sealing surface materials and applicable media

Sealing surface material

Use temperature °C

Hardness (HRC)

Applicable medium

Bronze

– 273 – 232

Water, seawater, air, oxygen, saturated steam

304, 316, 304L, 316L

– 268 – 316

14

Steam, water, oil, gas, liquefied gas, slightly corrosive and no erosion medium

17-4PH

– 40 – 400

40 – 45

A slightly corroded and erosive medium

CR13

– 101 – 400

In 37 – 42

A slightly corroded and erosive medium

Cobalt base alloy (STELLITE 6)

– 268 – 650

40 – 45 at room temperature

38 (600 ° C

With erosive and corrosive media

Monel alloy K

           S

– 240 – 482

27 – 35

30 – 38

Alkali, salt, food, acid solvent without air

Hastelloy H.B.

         H.C

371

538

14

23

Corrosive mineral acid, sulfuric acid, phosphoric acid, wet hydrochloric acid gas, chloric acid-free solution, strong oxidation medium

20 alloy

45.6 – 316

– 253 – 427

Oxidizing media and various concentrations of sulfuric acid

3. Bolt and nut materials

Common bolt and nut materials

ASTM bolt/nut materials

Applicable body material

A193 B7/A194 2H

WCB

A193 B7M/A194 2HM

NACE valves WCB

A193 B8/A194 8

Stainless steel valve CF8 CF8M CF3 CF3M

A193 B8M/A194 8M

Stainless steel valve CF8 CF8M CF3 CF3M

A320 L7/A194 4

Low-temperature valve LCB LCC

A320 L7M/A194 7M

Low-temperature valve LCB LCC

A193 B16/A194 4

High-temperature valve WC6 WC9 C5 C12

A193 B8A CLASS 1A/A194 8A

NACE valve CF8 CF8M CF3 CF3M

A193 B8MA CLASS 1A/A194 8MA

NACE valve CF8 CF8M CF3 CF3M

Four, valve seals

1. Packing

  • Valve packing is commonly used in graphite and PTFE packing;
  • Graphite filler can be divided into the braided filler and forming filler;
  • Formed graphite ring -250 – 650°C;
  • Stainless steel wire is woven flexible graphite -250 – 650°C;
  • Teflon impregnated graphite -200 – 280°C;
  • Low leakage graphite packing combination -250 – 650°C;
  • PTFE – 200 – 200 ° C.

2. Middle cavity gasket

  • PTFE plate;
  • Graphite plate;
  • Strong graphite pad;
  • Graphite stainless steel winding pad;
  • Stainless steel winding pad with PTFE;
  • RTJ metal pads;
  • Pressure seal metal seal ring.

3. The o-ring

  • NBR – 30 – 121 °C;
  • EPDM – 45 – 120 °C;
  • VITON A – 30 – 204 °C;
  • VITON B – 30 – 204 °C;
  • VITON AED (Anti Explosion Decompression) -30 – 204°C high pressure, small molecules such as CO2;
  • HNBR (HSN) -30 – 180°C.

4. Soft seal valve seat

  • PTFE – 200 – 200 ° C;
  • PCTFE – 250 – 150 ° C;
  • NYLON 1010 – 120 °C;
  • NYLON PA12-50 – 120 °C;
  • DEVLON V – 100 – 150 °C;
  • PEEK – 100 – 260 °C;
  • Polyphenylene – 400°C.

5. Medium temperature for soft sealing materials

NBR

CR

NR

EPDM

CSM HYPALON

HNBR

FKM

PTFE

Air or oxygen

2

1

3

1

2

1

1

1

Water up to 80 ° C

1

2

2

1

1

1

1

1

Water above 80 ° C

3

3

4

1

3

1

3

1

Dilute acids Dilute acid

3

3

3

2

4

1

1

1

Dilute alkalis Dilute alkali

2

2

2

1

1

2

2

1

Lower alcohols

1

1

2

1

1

1

4

1

Aldehydes acetaldehyde

3

3

3

1

3

2

4

1

Amines Amines

4

2

2

2

4

1

4

1

Chlorinated solvents chloride solvent

3

4

4

4

4

2

1

1

Ethers ether

4

4

4

3

4

4

3

1

Ketones ketone

4

4

4

1

4

4

4

1

Hydrocarbons – aliphatic hydrocarbon fat

1

2

4

4

2

1

1

1

Hydrocarbons, aromatic aromatic hydrocarbon

3

4

4

4

4

3

1

1

Leaded Petrol (gasoline)

2

3

4

4

4

2

1

1

Kerosene Kerosene

1

2

4

4

4

1

1

1

There are animal oils and fats

1

2

4

2

3

1

1

1

Fuel oils and diesel oils are Fuel oils

2

3

4

4

3

2

1

1

Lubricating oils of the Lubricating oils of the mineral Lubricating oils

1

2

4

4

4

1

1

1

Lubricating oils of all the Lubricating oils

2

3

4

4

4

1

2

1

Silicone oils and grease

1

1

1

1

1

1

1

1

Vegetable oils

1

3

4

3

2

1

1

1

The hydraulics mineral-based water-based fluid

1

3

4

4

2

1

1

1

Chlorinated chloride

4

4

4

4

4

4

2

1

Oil in water emulsions

3

4

4

4

4

2

1

1

Water in oil emulsions

3

4

4

4

3

2

1

1

Water-pending glycol-based liquor

1

3

3

1

1

2

2

1

Phosphate esters aliphatic

4

4

4

1

4

1

3

1

Phosphate esters-aromatic Phosphate

4

4

4

2

4

4

1

1

Minimum temperature (°C)

-30a

– 40

– 50

– 45

– 30

-30 a

– 15

– 200.

Maximum sustained temperature (°C)

120

120

100

120

120

180

200

250

Maximum instantaneous temperature (°C)

150

150

120

150

150

200

230

Hardness (IRHD)

40-90.

40-90.

40-85.

50-90.

65-80.

50-90.

50-98.

Five, butterfly valve material and allowable pressure

1. Gray cast iron (ASTM A216-B)

  • 125LB 2 to 12 “flanges allow working pressure of 200psi (1.4Mpa) up to 1.6Mpa;
  • 14 – 48 “flange allowable working pressure 150psi (1.0Mpa);
  • PTFE seat allows working pressure of 125psi (0.86Mpa).

2. Ductile iron

  • 150LB flange maximum allowable pressure 250psi.

6. NACE valve material

  • Commonly used main materials: carbon steel, stainless steel;
  • Common interior materials: CR13, 304, 316;
  • Material hardness ≤22HRC;
  • For CR13 heat treatment quenching + secondary tempering ≤22HRC;
  • 17-4pH solution quenching, secondary aging ≤33HRC;
  • Weld all base metal, heat affected zone, weld hardness ≤22HRC;
  • Electrode contains less than 0.1% nickel;
  • A105 hardness HB 187 or less.

7. Low temperature -46°C materials

  • Main material: LCB, LCC, LF2;
  • Inner material: 304, 316 (F6a is not commonly used, below -29°C should do impact test).

8. Low temperature -196°C materials

  • Main material: CF8, CF8M, 304, 316;
  • Inner material: 304, 316;
  • Sealing surface: double-sided cobalt base to prevent abrasion.

9. High-temperature valve with materials

  • Main material: WC6, WC9, C5, C12;
  • Inner material: 1Cr13 (above 454°C allowable stress than F304, F316), ASTM A638 660 (0Cr15Ni25Ti2MoAlVB), 20Cr1Mo1V1A;
  • Common sealing surface material: double-sided cobalt base to prevent abrasion.

Ten, stainless steel material performance comparison

Material

The performance comparison

316/316L

Containing Mo improves chloride and halide corrosion resistance and provides excellent tensile, creep, and stress fracture strength at high temperatures.

It is more resistant to atmospheric and moderate environmental corrosion than 304, resistant to 1 – 5% dilute sulfuric acid to 48°C, and resistant to some oxidizing acids 316 is not as resistant as 304.

When the temperature is between 427 °C and 817°C, it is easy to precipitate carbide, so it is easy to intergranular corrosion under welding conditions. Annealing after welding will restore the original corrosion resistance of 316.

The general corrosion resistance and other properties of the 316L are very similar to those of the 316, but it is resistant to intergranular corrosion under welding conditions or short-term conditions of 427 – 817°C. It is recommended that carbide precipitation is inevitable under welding conditions and no annealing is necessary after welding. Long-term exposure to the above temperature range can brittle the material and make it susceptible to intergranular corrosion.

Maximum continuous service temperature 899°C, intermittent temperature 817°C.

Resistance to chloride stress corrosion.

Non-hardening and non-magnetic in the annealing state, slightly magnetic in the cold hardening.

Better chloride corrosion resistance.

Application: nuclear energy, chemical, rubber, plastic, paper, pharmaceutical, textile; Heat exchanger, condenser, vaporizer.

347/347H

Containing Cb, recommended for welding where sufficient annealing is not possible, can also be used for transient temperature shocks from 427 to 871°C since the addition of Cb produces a stabilized stainless steel that eliminates intergranular corrosion caused by carbide precipitation.

Has higher corrosion resistance than 321, reduces the tendency of chromium carbide to form persistent reticular grain boundaries, has better high-temperature performance than 304/304L, and is typically used for transient heating to 817°C and sustainable service at 899°C.

347H contains higher carbon (0.04 – 0.10%), which has better high-temperature creep performance and improved intergranular corrosion resistance.

Used for high-temperature chemical process heat exchange pipe, oil refining, and high-temperature steam.

321/321H

It is an improved 304 containing Ti. Intergranular corrosion of hot carbonized sediments does not work. The addition of Ti eliminates the formation of chromium carbide at grain boundaries. Better high-temperature performance than 304/304L, usually for short heating to 817°C, sustainable use at 899°C. Susceptible to chloride stress corrosion.

Excellent field welding performance, 321H has higher carbon (0.04 – 0.10%) and better high-temperature creep performance.

Used for high-temperature chemical process heat exchange pipe, oil refining, and high-temperature steam.

Selection of valve materials

There are many materials for manufacturing valve parts, including various grades of ferrous and non-ferrous metals and their alloys. A variety of non-metallic materials. Manufacturing valve parts materials to be selected according to the following factors:

  • 1. The pressure of the working medium. Temperature and characteristics.
  • 2. The force of the part and the role played in the valve structure.
  • 3. Have good workmanship. 4.
  • 4. To meet the above conditions, to have a low cost.

Valve body. Materials for the bonnet and valve plate (valve flap)

  • I. Gray cast iron: gray cast iron is suitable for nominal pressure PN ≤ 1.0MPa, the temperature of -10 ℃ -200 ℃ water. Steam. Air. Gas and oil media. Common grades of gray cast iron are HT200. HT250. HT300. HT350.
  • II. Malleable cast iron: suitable for nominal pressure PN≤2.5MPa, the temperature of -30-300℃ water. Steam. Air and oil media, commonly used grades are KTH300-06. KTH330-08. KTH350-10.
  • III. Ductile iron: suitable for PN≤4.0MPa, the temperature of -30-350 ℃ water. Steam. Air and oil and other media. Commonly used grades are QT400-15. QT450-10. QT500-7.
  • IV. Carbon steel (WCA. WCB. WCC): for nominal pressure PN ≤ 32.0MPa, for the working temperature between -29 – +425 ℃ in the. High-pressure valves, including 16Mn. 30Mn working temperature of -29-595 ℃, commonly used instead of ASTM A105. commonly used grades are WC1. WCB. ZG25 and high-quality steel 20. 25. 30 and low alloy structural steel 16Mn.
  • V. Low-temperature carbon steel (LCB): for nominal pressure PN ≤ 6.4Mpa, temperature ≥ -196 ℃ ethylene, propylene, liquid natural gas, liquid nitrogen, and other media, commonly used grades are ZG1Cr18Ni9. 0Cr18Ni9. 1Cr18Ni9Ti. ZG0Cr18Ni9.
  • VI. Alloy steel (WC6. WC9), applicable to the working temperature between -29-595 ℃ non-corrosive media of high temperature and high-pressure valves; WC5. WC9 for the working temperature between -29-650 ℃ corrosive media of high temperature and high-pressure valves.
  • VII. Austenitic stainless steel, suitable for the working temperature between -196-+600 ℃ corrosive media valves.
  • VIII. Monel alloy: mainly applicable to valves for hydrogen and fluorine media.
  • IX. Copper alloy: mainly suitable for valves for oxygen pipeline with working temperature between -29-595℃.

The main applications of valves

In daily production life, we can see the valve, the valve mainly plays a switch or regulation role, from aerospace down to ordinary life water can see the valve figure, summarize the main application of the valve.

  1. Pipeline application valves, long-distance pipelines mainly for crude oil, finished products, and natural pipelines. This type of pipeline needs to use the majority of valves are forged steel three-body full bore ball valves, sulfur-resistant flat gate valves, safety valves, and check valves.
  2. Gas valves and city gas accounted for 22% of the entire natural whole market, the valve dosage is large, and its type is also more. The main need is for ball valves, plug valves, pressure-reducing valves, and safety valves.
  3. Environmental protection application valves, environmental protection systems at home, and water supply systems mainly need to use the centerline butterfly valve, soft seal gate valve, and ball valve exhaust valve (for the exclusion of air in the pipeline). Sewage treatment systems mainly need to use soft seal gate valves, and butterfly valves.
  4. Rural, urban heating with valves, and urban heat generation systems need to use a large number of metal seal butterfly valves, horizontal balance valves, and direct burial ball valves, because this type of valve solves the longitudinal and horizontal hydraulic disorder of the pipeline, to achieve energy saving, the purpose of heat generation balance
  5. Rural and urban construction application valves, an urban construction system with the general use of low-pressure valves, are currently developing in the direction of environmental protection and energy-saving. Environmentally friendly rubber plate valve, balancing valve and midline butterfly valve, metal sealed butterfly valve is gradually replacing the low-pressure iron gate valve. Domestic urban construction needs valves are mostly balancing valves, soft seal gate valves, butterfly valves, etc.
  6. For food and pharmaceutical application valves, the industry mainly needs to use stainless steel ball valves, non-toxic all-plastic ball valves, and butterfly valves. The above 10 major categories of valve products, general valve demand compared to the majority, such as instrumentation valves, needle valves, needle-shaped globe valves, gate valves, globe valves, check valves, ball valves, and butterfly valves mostly.
  7. Marine applications valve, following the development of offshore oilfield mining, the amount of marine flat hair needed for valves has gradually increased. Marine platforms need to use shut-off ball valves, check valves, and multiway valves.
  8. Metallurgical applications valve, metallurgical industry, alumina behavior mainly need to use wear-resistant slurry valve (in the flow type shut-off valve), regulating trap. The steel industry mainly needs to use metal seal ball valve, butterfly valve and oxidation ball valve, stop flash, and four-way reversing valve.
  9. Hydropower station application valves, the construction of China’s power stations are developing in the direction of large-scale, so the need for large-diameter and high-pressure safety valves, pressure reducing valves, globe valves, gate valves, butterfly valves, emergency blocking valves, and flow control valves, spherical seal instrumentation globe valves.
  10. Synthetic ammonia plant. Because the original ammonia synthesis and purification methods are different, the process is different, and the technical function of the required valve is also different. At present, the domestic ammonia plant mainly requires gate valves, globe valves, check valves, traps, butterfly valves, ball valves, diaphragm valves, regulating valves, safety valves, and high-temperature and low-temperature valves.
  11. Propylene clear device. The device generally needs to use the scale of production of valves, mainly gate valves, globe valves, check valves, ball valves, traps, needle-shaped globe valves, and plug valves, of which, gate valves account for about 75% of the total number of valves.
  12. Chemical fiber devices, chemical fiber products mainly polyester, acrylic, and vinyl in three categories. The ball valve, jacketed valve (jacketed ball valve, jacketed gate valve, jacketed globe valve of the valve it needs.

Preparation of valve model

The valve model shall generally indicate the valve type, driving mode, connection type, structural features, sealing surface material, valve body material, nominal pressure, etc. The standardization of the valve model provides convenience for valve design, selection, and sales. Nowadays, there are more and more types and materials of valves, and the model establishment of valves is becoming more and more complicated. Although there is a unified standard for valve model establishment in China, it is increasingly unable to meet the needs of valve industry development. For any new type of valve which can not use the standard number, all manufacturers can make models according to their own needs.
The standard valve model preparation method applies to an industrial pipeline Gate valve, throttle valve globe valve 、 butterfly valve 、 Diaphragm valve 、 Plunger valve 、 Plug valve 、 Check valve 、 Safety valve, pressure reducing valve Drain valve Etc. It includes the designation of the valve type and the designation of the valve.
Specific compilation method of valve model

The following is the sequence diagram of each code in the standard valve model preparation method:

20220726101219 55957 - A Complete Guide to Valves

Understanding the diagram on the left is the first step to understanding various valve models. Here is an example to give you a general understanding:
Valve model: “Z961Y-100I DN 150” is a complete gate valve model. The final “DN 150” is not included in the compilation, which means the valve diameter is 150 mm, which is easy to understand. The front part: “Z961Y-100I” is seated according to the sequence diagram above, as follows:
“Z” is 1 unit; “9” is 2 units; “6” is 3 units; “1” is 4 units; “Y” is 5 units; “100” is 6 units; “I” is unit 7
The meaning of this valve model is gate valve, electric drive, welding connection, wedge single gate, cemented carbide seal, 10MPa pressure, chrome-molybdenum steel valve body material.
Unit 1: valve type code
Type
Safety valve
Butterfly valve
Diaphragm valve
Check valve
(bottom valve)
Globe valve
Throttle valve
Blowdown valve
Globe valve
Drain valve
Plunger valve
Plug valve
Pressure relief valve
Gate valve
Code name
A
D
G
H
J
L
P
Q
S
U
X
Y
Z
For valves with other functions or special mechanisms, a Chinese character should be added before the valve type code
Pinyin alphabet, as specified in the following table:
Type
Thermal insulation
Low-temperature type
Fireproof type
Slowly closed type
Deslagging type
Fast type
(Stem seal) Bellows type
Code name
B
D
F
H
P
Q
W
Unit 2: transmission mode
Transmission
mode
Electromagnetism
Electromagnetic hydraulic
Electro-hydraulic
Worm gear
Spur gear
Bevel gear
Pneumatic
Hydrodynamics
Pneumatic fluid
Electric
Handle
handwheel
Code name
0
1
2
3
4
5
6
7
8
9
No code
Three units: connection type
Connection mode
Internal thread
External thread
Two different connections
Flange
Welding
Counter clamp
Clamp
Ferrule
Code name
1
2
3
4
6
7
8
9
Unit 4: structural type
Structural type code of gate valve
Structural style
Code name
Stem lifting type
(rising pole)
Wedge gate
Elastic RAM
0
Rigid gate
Single ram
1
Double ram
2
Parallel gate
Single ram
3
Double ram
4
Nonlifting stem
(concealed rod)
Wedge gate
Single ram
5
Double ram
6
Parallel gate
Single ram
7
Double ram
8
Code of structure type of stop valve, throttle valve, and plunger valve
Structural style
Code name
Structural style
Code name
Disc unbalanced
Straight channel
1
Disc balanced
Straight channel
6
Z-channel
2
Angle channel
7
Tee channel
3
Angle channel
4
Direct flow channel
5
Code of the ball valve structure
Structural style
Code name
Structural style
Code name
Floating ball
Straight channel
1
Fixed ball
Straight channel
7
Y-shaped tee
2
Four-way channel
6
L-shaped tee
4
T-shaped tee
8
T-shaped tee
5
L-shaped tee
9
Hemispherical straight through
0
Code of the butterfly valve structure
Structural style
Code name
Structural style
Code name
Sealed type
Single eccentricity
0
Unsealed
Single eccentricity
5
Center vertical plate
1
Center vertical plate
6
Double eccentricity
2
Double eccentricity
7
Three eccentricities
3
Three eccentricities
8
Linkage mechanism
4
Linkage mechanism
9
Code of the diaphragm valve structure
Structural style
Code name
Structural style
Code name
Ridge channel
1
Straight channel
6
Direct flow channel
5
Y-shaped angle channel
8
Code of the plug valve structure
Structural style
Code name
Structural style
Code name
Packing seal
Straight channel
3
Oil seal
Straight channel
7
T-shaped tee
4
T-shaped tee
8
Four-way channel
5
Code of the check valve structure
Structural style
Code name
Structural style
Code name
Lifting disc
Straight channel
1
Swing disc
UNIVALVED structure
4
Vertical structure
2
Multilobed structure
5
Angle channel
3
Bicuspid structure
6
Butterfly check type
7
Structural code of safety valve
Structural style
Code name
Structural style
Code name
Spring loaded spring seal structure
Full open type with heat sink
0
Spring load spring not closed and with wrench structure
Micro lift, double valve
3
Micro open
1
Micro open
7
Full swing
2
Full swing
8
Full open type with a wrench
4
Lever type
Single lever
2
Full open type with a control mechanism
6
Double lever
4
Pulse type
9
Code of structure type of pressure reducing valve
Structural style
Code name
Structural style
Code name
Membrane type
1
Bellows type
4
Spring film type
2
Lever type
5
Piston type
3
Steam trap Structure code
Structural style
Code name
Structural style
Code name
Floating ball
1
Steam pressure type or capsule type
6
Floating bucket
3
Bimetallic chip
7
Liquid or solid expansion type
4
Pulse type
8
Bell float type
five
Disc type
nine
Code of the drain valve structure
Structural style
Code name
Structural style
Code name
Level connection drain
Cut off straight through
1
Intermittent discharge of liquid bottom
Cut off DC type
5
Cut off angle type
2
Cut off straight through
6
Cut off angle type
7
Floating gate type straight through type
8
Unit 5: material code of sealing surface and lining
Sealing surface or lining material
Tin-based bearing alloy (Babbitt)
Enamel
Nitriding steel
Fluoroplastics
Ceramics
Cr13 Stainless Steel
Rubber lining
Monel alloy
Code name
B
C
D
F
G
H
J
M
Sealing surface or lining material
Nylon plastics
Boronizing steel
Lead lining
austenitic stainless steel
Plastic
copper alloy
rubber
Cemented carbide
Code name
N
P
Q
R
S
T
X
Y
Unit 6: nominal pressure value
Expressed directly in Arabic numerals, the value is 10 times the value in MPA units
Unit 7: valve body material
Valve body
Material Science
Titanium and
titanium alloy
Carbon steel
Cr13 series
stainless steel
Chromium molybdenum steel
Malleable iron
Aluminum alloy
18-8 series
stainless steel
Ductile iron
Mo2ti system
stainless steel
Plastic
Copper and
copper alloy
Cr Mo V steel
Gray cast iron
Code name
A
C
H
I
K
L
P
Q
R
S
T
V
Z
This item is omitted for gray cast iron low-pressure valve and steel medium pressure valve.

What is the seat of the valve?

The valve seat is a removable surface part within the valve, used to support the spool fully closed position, and constitutes a sealing vice. The general seat diameter is the maximum diameter of the valve flow. For example, butterfly valve seat material is very wide, and all kinds of rubber, plastic and metal materials can be used as seat material, such as EPDM, NBR, NR, PTFE, PEEK, PFA, SS315, STELLITE, and so on.

20220726104202 40804 - A Complete Guide to Valves

Selection of valves

In the fluid piping system, regulating valve is the control element, and its investment accounts for about 30%-50% of the pipeline project cost. The main functions of the valve are opening and closing, throttling, regulating the flow, isolating equipment and pipeline systems, preventing the backflow of media, regulating and draining pressure, etc… Valve is also the most complex component in the pipeline, it is generally assembled from multiple parts, high technical content. With the rapid development of the petrochemical industry, petrochemical production equipment in the media mostly toxic, flammable, explosive, and corrosive characteristics, the operating conditions are more complex and demanding, operating temperature and pressure are high, the start-up cycle is long, once the valve failure, the light leads to media leakage, both pollution of the environment and economic losses, the heavy lead to device shutdown, or even cause malignant accidents. Therefore, in the pipeline design, a scientific and reasonable selection of valves can reduce the construction costs of the device, and also ensure the safe operation of production. We introduced a variety of commonly used valves such as gate valves, globe valves, throttle valves, plug valves, ball valves, diaphragm adjustment valves, and other selection methods.

The significance of the correct selection of valves

The correct selection of valves is essential to ensure the safe production of the device, improve the service life of the valve and meet the long-cycle operation of the device. The main reason for many valve accidents is the improper selection of valves, such as the use of cast iron valves in cold regions, because the oil contains water accumulated in the valve body, and during winter freezing is easy to freeze and crack the valve. In some pump body export valves, for some reason, the required flow is low and on the occasion of the larger power of the matching pump, often use the valve off to adjust the flow of small approach. The operation, due to the gate plate’s partial opening, vibration, accelerating the wear of the gate and seat sealing surface, is easy to cause valve leakage. In addition, the quality of the valve has a great impact on production and use.

The principles of the selection of valves

(1) Reliability

Power production requires a continuous, smooth, and long-cycle operation. Therefore, the requirements of the valve should be highly reliable, a large safety factor, not because of valve failure caused by major production safety and personal injury or death; to meet the requirements of the device’s long-cycle operation, long-cycle continuous production is the benefit; in addition, to reduce or avoid the valve caused by the “run, bubble, drip, leak” to create a clean, civilized plant.

(2) To meet the process production requirements

The valve should meet the operating medium, pressure and temperature, and user needs, which are also the most basic requirements for the selection of valves. For example, the need for valves to protect the role of overpressure, the discharge of excess media, safety valves, and relief valves should be selected; the need to prevent the operation of the media backflow, check valves should be used; the need to automatically remove steam piping and equipment in the continuous generation of condensate, air, and other non-condensable gases, while preventing the escape of steam, should be selected traps. In addition, for corrosive media, a corrosion-resistant material valve body should be used.

(3) Operation, installation, inspection (maintenance), and repair convenience

Valve installation should enable the operator to correctly identify the valve direction, opening signs, and indication signals, to facilitate the timely and decisive handling of various emergency failures. At the same time, the selected valve type structure should be as simple as possible, easy to install, and inspection (maintenance) repair.

(4) Economy

Pay attention to saving investment, and reducing the cost of the device; several different valve types can meet the requirements of use, should be selected inexpensive, simple structure of the valve; ordinary materials can meet the requirements of use, should not be selected higher grade materials.

Steps and basis for selecting valves

Steps to select the valve.

  1. Define the use of the valve in the equipment or device, and determine the working conditions of the valve: applicable media, working pressure, working temperature, etc.
  2. Determine the nominal diameter of the pipeline connected to the valve and the connection: flange, thread, welding, etc.
  3. To determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage, etc.
  4. According to the pipeline transport medium, working pressure, and working temperature to determine the selected valve shell and internal parts of the material: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc.
  5. Select the type of valve: closed-circuit valves, regulating valves, safety valves, etc.
  6. Determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc.
  7. To determine the parameters of the valve: for automatic valves, according to different needs to determine the allowable flow resistance, discharge capacity, back pressure, etc., and then determine the nominal diameter of the pipeline and the diameter of the seat hole.
  8. Determine the geometric parameters of the selected valve: the length of the structure, flange connection form, and size, the size of the valve height direction after opening and closing, the size and number of connected bolt holes, and the entire valve external dimensions, etc.
  9. Use the available information: valve catalog, valve product samples, etc. to select the appropriate valve products.

The basis for selecting valves.

Understanding the steps to master the selection of valves, should further understand the basis for the selection of valves.

  1. The use of the selected valve, the use of working conditions, and manipulation control mode.
  2. The nature of the working medium: working pressure, working temperature, corrosive properties, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive media, the viscosity of the medium, and so on.
  3. The requirements of the valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing grade, etc.
  4. Installation size and size requirements: nominal diameter, pipeline connection, connection size, size or weight restrictions, etc.
  5. Additional requirements for the reliability of the valve product, service life, and explosion-proof performance of the electric device.

In selecting the parameters of the valve should be noted.

If the valve is to be used for control purposes, the following additional parameters must be determined: method of operation, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop when closed, and maximum and minimum inlet pressure of the valve. 

Based on the above basis and steps for selecting valves, a reasonable and correct selection of valves must also be based on a detailed understanding of the internal structure of the various types of valves so that the right choice can be made for the preferred valve.

The final control of the pipeline is the valve. Valve openings and closings control the way the medium flows in the pipeline, and the shape of the valve flow channel so that the valve has certain flow characteristics, which must be taken into account when selecting the most suitable valve for installation in the pipeline system.

The principles to be followed when selecting a valve

1. Cut-off and open media with the valve

The flow path is straight through the valve, the flow resistance is small, usually selected as the valve for shut-off and open media. Downward closing type valve (globe valve, plunger valve) due to its flow path zigzag, flow resistance than other valves, so less choice. On the occasion of allowing a higher flow resistance, closed-type valves can be used.

2. Control the flow of valves

Usually, choose easy to adjust the flow of the valve as a control flow. A downward closing type valve (such as a shut-off valve) is suitable for this purpose because its seat size is proportional to the relationship between the stroke of the closing member. Rotary valves (plug valves, butterfly valves, ball valves) and flexure body type valves (clamping valves, diaphragm valves) can also be used for throttling control, but usually only in a limited range of valve bore. A gate valve is a disc-shaped gate to the circular seat mouth to do cross-cutting movement, it is only close to the closed position, to better control the flow, so it is usually not used for flow control.

3. The valve for reversing and shunting

According to the need for a directional shunt, this valve can have three or more channels. Plug and ball valves are more suitable for this purpose, therefore, most of the valves used for directional flow diversion are selected for one of these types of valves. But in some cases, other types of valves, as long as two or more valves are properly connected to each other, can also be used for directional flow diversion.

4. With suspended particles in the media with the valve

When the medium with suspended particles, the most suitable for the use of its closing member along the sealing surface of the sliding with wiping effect of the valve. If the closing member to the seat of the back and forth movement is vertical, then it may hold particles, so this valve unless the sealing surface material can be allowed to embed particles, or only for basic clean media. Ball valves and plug valves have a wiping effect on the sealing surface during opening and closing, so they are suitable for use in media with suspended particles.

How to choose the valve

Valves have different requirements according to their types and use, mainly sealing, strength, regulation, circulation, and opening and closing properties. In the design and selection of valves, in addition to the basic parameters and performance, also consider the performance of the fluid, including the phase state of the fluid (gas, liquid, or containing solid particles), corrosion, viscosity, toxicity, flammability and explosiveness, precious and rare degree and radioactivity.

The correct choice of valves

Valve selection is an important part of proper design and maintenance practices for industrial, piping, and instrumentation systems. Without the correct valve for a specific application, operators may be exposed to improper or inferior fluid system performance, longer downtime, and avoidable safety risks.

Valves are typically selected in the initial stages of fluid system design. Throughout the life of the system, maintenance technicians typically replace valves and most other components according to specifications using the same types of components already in the system. Therefore, it is especially important to select the correct valve from the beginning to help operators avoid premature valve replacement later.

How do you make the right choice?

To make the right valve selection, designers and technicians need to consider the valve size, temperature, application, media, pressure, end or fitting, and delivery. Full consideration of each of these operating conditions can guide industrial fluid and analytical sampling system professionals in selecting the correct valve.

S: Size

The size of a valve determines its flow rate and needs to correspond to the desired (or required) flow rate of the system. The manufacturer will provide a flow coefficient (Cv) that represents the relationship between the pressure drop at each end of the valve and the corresponding flow rate.

The flow coefficient or Cv is the amount of water (in gallons) per minute flowing through a valve with a pressure drop of 1 psi at 60°F. For compressible fluids like natural gas, calculating and using the Cv parameter to predict flow is more complex, but still provides a valid method of valve sizing for a given application.

Valve design factors that affect Cv include the size and geometry of the flow path; the orifice size of a valve affects the flow of fluid through it. The larger the orifice, the greater the potential flow rate. Orifices can vary greatly between valve types; for example, a ball valve will provide little flow resistance, but a needle valve will restrict or slow the flow rate. These should be considerations in your selection process.

If in doubt, consult your manufacturer; a good manufacturer will help you determine the size of valve you need.

T: Temperature

Keep in mind the operating temperature of your valve. This includes the temperature of the system media your valve will help control and the ambient operating temperature of the surrounding environment. Ask yourself, “Will these temperatures remain constant, or will they change frequently?” These conditions may affect your valve selection or the frequency with which preventive maintenance needs to be performed.

Consider temperature fluctuations that may cause seal materials to expand and contract. In addition, metal parts may lose strength at high temperatures, which can reduce pressure ratings. Always contact your manufacturer to ensure that the valve has been fully tested under extreme conditions.

A: Application

Consider what the valve needs to do in your system. Do you need to start or stop the flow of media? Regulate flow levels? Control flow direction? Protect the system from overpressure?

Your answers to these questions will guide the type of valve you choose for your design. Again, use a simple two-way ball valve as an example. While some ball valves from other manufacturers can provide throttling, most ball valves should not be used to throttle or regulate flow, but rather in a fully open or fully closed position. If your goal is to throttle or regulate flow, a needle valve or metering valve may be a better choice.

M: Media

When you are trying to select the correct valve with the proper material composition, you should also carefully consider the fluid media within the system. Make sure the system media is compatible with the materials that make up the valve body, seat, stem tip, and other softer materials. Incompatibility can lead to corrosion problems, embrittlement, or stress corrosion cracking – all of which pose safety risks as well as costly production problems.

As with temperature, you should also consider the location where the valve is used. Will it be operating in a climate-controlled environment, such as inside a plant or in a heated instrument enclosure? Will it be for outdoor use, exposed to climatic factors such as direct sunlight, rain, snow, frost, ice, and temperature fluctuations? A marine environment with significant exposure to chlorides? Valves and their components are available in a variety of materials. Select valves that are suitable for these factors to maximize valve life and enhance valve functionality.

P: Pressure

Pressure is another important consideration when selecting a valve. Note the two contexts in which this term is used.

Operating Pressure: The normal operating pressure in your system.

Design pressure: The maximum pressure limit provided by the valve manufacturer; never exceed the design pressure of any fluid system component except under controlled test conditions.

The pressure limit of a fluid system is based on its minimum rated components-keep this in mind when selecting a valve. The pressure and temperature of the process fluid can have a significant effect on component performance. The valve you select needs to withstand pressure and operate over a wide range of temperatures and pressures when needed. Design, material selection, and verification are all critical aspects of valve performance. It is also important to remember that pressure and temperature have a strong influence on each other. Typically, as the process fluid temperature increases, the rated working pressure will decrease.

E: End Connections

Valves come with a variety of different end connections. These may be indispensable tube fittings, pipe threads, pipe flanges, welded ends, etc. Although not traditionally associated with the construction of the valve, the choice of end connections is critical to the overall construction of the valve and its ability to maintain a sealing system. Make sure your end connections are suitable for your system pressure and temperature and are properly sized – the correct end connections simplify installation and avoid additional leak points.

D: Delivery

After considering all these factors and selecting the right valve for your application, ask yourself, “When do I need a valve? How many do I need?

As with any other factor, on-time delivery and reliable supply are important to keep your fluid system operating and efficient. As a final step in the STAMPED approach, review your suppliers. When you need parts, are they available to meet the demand? Are they easy to reach? Will they work with you to understand your system needs?

Valve selection is essential to designing safe, efficient fluid systems.

How do I calculate the size of a valve?

To calculate the size of a valve, you need to know the parameters associated with the operation of the circuit.

Parameters for sizing valves.

  • Pressure
  • Temperature
  • Flow rate
  • Diameter

Pressure is an important factor that must be taken into account, on the one hand, to avoid undersizing the valve, which could lead to problems in valve leakage or rupture, and on the other hand to avoid oversizing the valve.

The operating temperature, i.e. the temperature of the circulating medium, and the ambient temperature around the valve body need to be determined. It is important to know the temperature extremes that the valve needs to withstand to be able to select the valve that can be used to operate under these conditions, especially the materials used to manufacture the body, shut-off system, and seals.

The operating pressure, i.e., the pressure at which the medium will circulate through the valve.

Flow rate and velocity of the fluid. The flow rate and rated velocity are essential elements to help you select the right valve, especially for regulating that flow. The flow coefficient (Kv) is a theoretical value specified by the manufacturer that allows you to calculate the nominal flow rate of the valve. It can be expressed in liters per minute (l/min) or cubic meters per hour (m3/h). The valve manufacturer provides charts to determine this coefficient based on the required flow rate and nominal diameter.

The nominal diameter (DN) of the circuit in which the valve is located. This is essential to avoid oversizing the valve, which may lead to unstable operation of the equipment, or to avoid undersizing, which may lead to a significant pressure drop and rapid valve damage.

Various valve selection techniques and test pressure methods

In general, industrial valves in use do not do strength tests, but after repairing the valve body and cover or corrosion damage to the valve body and cover should do strength tests. For the safety valve, its rectification pressure and back-to-the-seat pressure, and other tests should be by its instructions and the provisions of the relevant regulations. Valve installation should be a strength and sealability test. Low-voltage valve spot checks 20%, such as failure should be 100% of the inspection; medium and high-pressure valves should be 100% of the inspection. Valve test pressure commonly used media are water, oil, air, steam, nitrogen, etc., various types of industrial valves including pneumatic valves test pressure methods are as follows.

1. The ball valve pressure test method

A pneumatic ball valve strength test should be carried out in the half-open state of the sphere.

  • ① Floating ball valve sealing test: the valve is in a half-open state, one end of the introduction of the test medium, the other end closed; the ball will be rotated several times, and the valve is closed when the closed end of the open check while checking the packing and gasket at the sealing performance, there shall be no leakage. Then introduce the test medium from the other end, and repeat the above test.
  • ② Fixed ball valve sealing test: Before the test, the ball will be idle and rotate a few times, fixed ball valve is closed, from one end of the introduction of the test medium to the specified value; use a pressure gauge to check the sealing performance of the introduced end, the use of pressure gauge accuracy 0.5-1 level, the range of the test pressure 1.5 times. In the specified time, no pressure drop phenomenon is qualified; then introduce the test medium from the other end, and repeat the above test. Then, the valve will be half-open state, both ends closed, and the cavity is full of media, check the packing and gasket at the test pressure, there shall be no leakage.
  • ③ Three-way ball valve should be tested in each position for tightness.

2. The check valve test pressure method

Check valve test state: lift check valve flap axis is in a vertical position with the horizontal; swing check valve channel axis and flap axis is in a position approximately parallel to the horizontal line.

Strength test, the introduction of test media from the inlet end to the specified value, the other end closed, see the valve body and valve cover no leakage for qualified.

The sealing test is qualified by introducing the test medium from the outlet end, checking the sealing surface at the inlet end, and no leakage at the packing and gasket.

3. Testing method of pressure reducing valve

① Strength test of pressure reducing valve is generally assembled after the single piece test, or assembled after the test. Duration of a strength test: DN<50mm min; dn65-150mm more than 2min; dn>150mm more than 3min. After welding of bellows and components, 1.5 times of the highest pressure after applying pressure reducing valve, strength test with air.

② Sealability test according to the actual working medium. When testing with air or water, 1.1 times the nominal pressure for the test; when testing with steam, the highest working pressure allowed under the working temperature. The difference between the inlet pressure and outlet pressure is not less than 0.2MPa, and the test method is: after the inlet pressure is set, gradually adjust the adjusting screw of the valve so that the outlet pressure can change sensitively and continuously within the maximum and minimum values, without stagnation and blocking. For steam pressure reducing valve, when the inlet pressure is adjusted away, close the valve after the cut-off valve, the outlet pressure is the highest and lowest value, within 2min, its outlet pressure should be by the provisions of Table 4.176-22, at the same time, the volume of the pipe after the valve by the provisions of Table 4.18 for qualified; for water, air pressure reducing valve, when the inlet pressure is adjusted, the outlet pressure is zero, close the pressure reducing valve for sealing test, in No leakage within 2min is qualified.

4. The test pressure method of a butterfly valve

The strength test of the pneumatic butterfly valve is the same as that of the globe valve. Butterfly valve sealing performance test should be introduced from the media flow end of the test medium, the butterfly plate should be opened, the other end closed, inject pressure to the specified value; check the packing and other sealing place no leakage, close the butterfly plate, open the other end, check the butterfly plate sealing place no leakage for qualified. The butterfly valve used for regulating the flow may not do the sealing performance test.

5. The test pressure method of the plug valve

① When the strength test of the plug valve, the medium is introduced from one end, close the rest of the pathway, the plug will be rotated in turn to the full open working position for the test, and the valve body is not found to be leaking for qualified.

② Sealing test, a straight-through plug should keep the cavity and access pressure equal, the plug will be rotated to the closed position, from the other end to check, and then rotate the plug 180 ° to repeat the above test; three-way or four-way plug valve should keep the cavity and access pressure equal at one end, the plug will be rotated to the closed position, in turn, the pressure is introduced from the right-angle end, from the other end to check at the same time.

Plug valve test before allowing a layer of non-acidic thin lubricant on the sealing surface, no leakage and expanding water droplets found in the specified time for qualified. Plug valve test time can be shorter, generally according to the nominal diameter of the provisions of 1 – 3min.

The plug valve for gas should be 1.25 times the working pressure for the air tightness test.

6. Diaphragm valve pressure test method

Diaphragm valve strength test from either end of the introduction of the medium, open the valve flap, the other end closed, test pressure up to the specified value, see the valve body and valve cover no leakage for qualified. Then lower the pressure to the sealing test pressure, close the valve flap, and open the other end for inspection, no leakage for qualified.

7. Test pressure method of shut-off valve and throttle valve

Globe valve and throttle valve strength test, usually the assembled valve in the pressure test frame, open the valve flap, inject the medium to the specified value, check whether the valve body and valve cover sweat and leakage. A strength test can also be done for a single piece. A sealing test is done only for shut-off valves. Test the stem of the globe valve into a vertical state, the valve flap open, the media from the bottom end of the valve flap introduced to the specified value, check the packing and gasket; to be qualified to close the valve flap, open the other end to check whether there is leakage. If the valve strength and sealing test are to be done, the strength test can be done first, and then lower the pressure to the specified value of the sealing test, check the packing and gasket; then close the valve flap, open the export end to check whether the sealing surface leakage.

8. The gate valve pressure test method

The gate valve strength test is the same as the globe valve. There are two ways to test the sealing of the gate valve.

① Gate open, so that the pressure in the valve to the specified value; then close the gate, immediately remove the gate valve, check whether there is leakage on both sides of the gate seal or directly to the plug on the valve cover inject test medium to the specified value, check the seal on both sides of the gate. The above method is called the intermediate test pressure. This method is not suitable for sealing tests in the gate valve below the nominal diameter of DN32mm.

② Another method is to open the gate so that the valve tests pressure up to the specified value; then close the gate, open one end of the blind, and check whether the sealing surface is leakage. Then reverse the head, and repeat the above test until qualified.

Pneumatic gate valve packing and gasket at the sealing test should be carried out before the gate sealing test.

9. The safety valve pressure test method

① Safety valve strength test and other valves are the same as water for the test. When testing the lower part of the valve body, the pressure is introduced from the I = I end, and the sealing surface is closed; when testing the upper part of the valve body and valve cover, the pressure is introduced from the El end, the other end is closed. In the specified time valve body and valve cover no leakage phenomenon for qualified.

② Sealing test and pressure test, the general use of media are steam safety valve with saturated steam as the test medium; ammonia or other gases with the valve with air as the test medium; water and other non-corrosive liquids with the valve with water as the test medium. For some important positions, the safety valve commonly used nitrogen as the test medium.

Seal test to the nominal pressure value for the test pressure, the number of times not less than two, no leakage in the specified time for qualified. There are two methods of leak detection: one is to seal the connections of the safety valve, using butter to seal the thin paper paste in the out El flange, thin paper bulging for leakage, not bulging for qualified; second, using butter to seal the thin plastic plate or other plates in the lower part of the export flange, water seal valve flap, test water does not bubble for qualified. Safety valve pressure setting and back to the seat pressure test not less than three times, by the provisions of the qualified. For safety valve performance test see GB / T12242-1989 safety valve performance test methods.

Key points of valve selection

1. Clarify the use of the valve in the equipment or device

Determine the working conditions of the valve: the nature of the applicable medium, working pressure, working temperature and manipulation control mode, etc.

2. Correctly select the type of valve

The correct choice of valve type is based on the designer’s full mastery of the entire production process, and operating conditions as a prerequisite, in the selection of valve type, the designer should first master the structural characteristics and performance of each valve.

3. Determine the end connection of the valve

The threaded connection, flange connection, and welding end connection, are the first two most commonly used. The threaded connection of the valve is mainly the nominal diameter of the valve below 50 mm, if the size of the diameter is too large, the installation and sealing of the connection are very difficult.

Flange connection of the valve, its installation, and disassembly are more convenient but bulkier than the threaded connection of the valve, the price is higher, so it is suitable for a variety of through diameter and pressure of the pipeline connection.

Welded connections are more reliable than flange connections under more demanding conditions. But the welded connection of the valve disassembly and reinstallation is more difficult, so its use is limited to usually reliable long-term operation, or the use of harsh conditions, and high-temperature occasions.

4. Valve material selection

Select the valve shell, internal parts, and sealing surface materials, in addition, to considering the physical properties of the working medium (temperature, pressure) and chemical properties (corrosive), but also to master the degree of cleanliness of the medium (with or without solid particles), in addition, but also concerning the relevant provisions of the state and the use of the department.

The correct and reasonable choice of valve material can obtain the most economical service life of the valve and the best use of performance. Valve body material selection order: cast iron – carbon steel – stainless steel, sealing ring material selection order: rubber – copper – alloy steel – F4.

5. Other

In addition, should determine the flow of fluid through the valve and pressure level, etc., the use of available information (such as valve catalogs, valve product samples, etc.) to select the appropriate valve.

1. How to choose the gate valve

In general, the gate valve should be preferred. In addition to the gate valve for steam, oil, and other media, but also for media containing granular solids and viscosity, and for bleeding and low vacuum system valves. For the media with solid particles, the gate valve body should have one or two blowing holes. For low-temperature media, a special low-temperature gate valve should be used.

2. How to choose the shut-off valve

Globe valve is suitable for the fluid resistance requirements are not strict on the pipeline, that is, the pressure loss is not considered large, as well as high temperature, high-pressure media pipeline or device, for DN <200mm steam and other media pipeline; small valves can be used to a cut-off valve, such as needle valve, instrumentation valve, sampling valve, manometer valve, etc.; cut-off valve has a flow adjustment or pressure adjustment, but the adjustment accuracy requirements are not high, and the pipeline diameter and For highly toxic media, it is appropriate to use the bellows-sealed globe valve, but the globe valve should not be used for viscous media and media containing particles that are easy to precipitate, but also not for venting valves and low vacuum system valves.

3. How to choose a ball valve

Ball valves are suitable for low temperature, high pressure, viscous media. Most ball valves can be used in media with suspended solid particles, according to the material requirements of the seal can also be used for powder and granular media; full-channel ball valves are not suitable for flow regulation, but suitable for the requirements of rapid opening and closing of the occasion, to facilitate the realization of the accident emergency cut off; usually in strict sealing performance, wear, indented channel, rapid opening and closing action, high pressure cut-off (large differential pressure), low noise, the phenomenon of gasification, operation Small torque, small fluid resistance in the pipeline, the recommended use of ball valves; ball valves are suitable for light structure, low-pressure cut-off, corrosive media; ball valves are also the most ideal valve for low temperature, deep cold media, low-temperature media piping systems and devices, it is appropriate to use plus the cover of the low-temperature ball valves; the choice of floating ball ball valve seat material should take the load of the ball and the working medium, large-diameter ball valves require greater operating Force, DN ≥ 200mm ball valve should be selected in the form of worm gear transmission; fixed ball valve for larger diameter and higher pressure occasions; in addition, the ball valve for process highly toxic materials, combustible media pipeline, should have a fire, anti-static structure.

4. How to choose throttle valve

A throttle valve is suitable for low media temperature, and high-pressure occasions, suitable for the need to regulate the flow and pressure parts, not suitable for viscosity and solid particles containing media, and not suitable for an isolation valve.

5. How to choose the plug valve

Plug valve is suitable for the occasion requiring fast opening and closing, generally not suitable for steam and higher temperature media, for lower temperature, viscosity media, also suitable for media with suspended particles.

6. How to choose a butterfly valve

A butterfly valve is suitable for larger diameter (such as DN>600mm) and short structure length requirements, as well as the need for flow regulation and opening and closing requirements for fast occasions, generally used for temperature ≤ 80 ℃, pressure ≤ 1.0MPa water, oil, and compressed air and other media; due to butterfly valve compared to the gate valve, ball valve pressure loss are relatively large, so the butterfly valve is suitable for pressure loss requirements in the pipeline system is not strict.

7. How to choose to check valve

The check valve is generally suitable for clean media, and should not be used for media containing solid particles and large viscosity. When DN ≤ 40mm, it is appropriate to use the lift check valve (only allowed to be installed in the horizontal pipeline); when DN = 50-400mm, it is appropriate to use the swing lift check valve (in the horizontal and vertical pipeline can be installed, such as installed in the vertical pipeline, the media flow direction from the bottom up); when DN ≥ 450mm, it is appropriate to use the buffer type check valve; when DN = 100-400mm can also choose to clamp check valve; Swing check valve can be made into a very high working pressure, PN can reach 42MPa, according to the shell and seal material can be applied to any working medium and any working temperature range. The medium is water, steam, gas, corrosive media, oil, drugs, etc. The medium working temperature range is between -196-800℃.

8. How to choose a diaphragm valve

The diaphragm valve is suitable for working temperature less than 200 ℃, pressure less than 1.0MPa oil, water, acidic media, and media containing suspension, not for organic solvents and strong oxidant media; abrasive granular media should be selected weir type diaphragm valve, select weir type diaphragm valve to refer to its flow characteristics table; viscous fluid, cement slurry, and sedimentation media should be selected straight through diaphragm valve; in addition to specific requirements, diaphragm valve should not be used for vacuum piping and vacuum equipment.

Valve applications, operating frequencies, and services vary widely, to control or eliminate even the slightest leakage, the most important and critical equipment is still the valve. Learning to select the correct valve is essential.

Summary of valve selection

The above analysis shows that, in general, the gate valve should be preferred.

Globe valve is suitable for the fluid resistance requirements are not a strict pipeline, as well as high temperature, high-pressure media pipeline or device, should not be used for viscosity and contains particles of the media, but also not for venting valve and low vacuum system valves.

Ball valves are suitable for low temperature, high pressure, viscous media, usually used in the sealing performance is strict, wear, indentation channel, rapid opening, and closing action, differential pressure, low noise, vaporization phenomenon, small operating torque, small fluid resistance pipeline.

The throttle valve is suitable for low media temperature and high pressure, not suitable for viscosity and media containing solid particles, and not suitable for isolation valve.

A plug valve is suitable for the occasion requiring fast opening and closing, generally not applicable to steam and higher temperature media, for lower temperature, the viscosity of the media, also suitable for media with suspended particles.

A butterfly valve is generally used for temperature ≤ 80 ℃, pressure ≤ 1.0 MPa of water, oil, compressed air, and other media; because the butterfly valve is compared to the gate valve, ball valve pressure loss is relatively large, so the butterfly valve is suitable for the pressure loss requirements of the pipeline system is not strict.

The check valve is generally suitable for clean media, and should not be used for media containing solid particles and large viscosity. Diaphragm valves are suitable for oil, water, acidic media, and media containing suspended matter with a working temperature of less than 200℃ and pressure of less than 1.0MPa, but not suitable for organic solvents and strong oxidant media.

In the pipeline system of petroleum, chemical, and other industries, the valve application, operation frequency, and service are varied, to control or eliminate low leakage, the most important and critical equipment is the valve. Proper selection of valves can reduce the construction cost of the device and ensure the safe operation of production.

Acceptance of the valve

Valve acceptance criteria

1. Acceptance purpose

Through acceptance, the number and appearance of the incoming valves can be checked and gate-checked to prevent damage to the appearance of quality, quantity, and other problems occurring during the manufacturer’s several means of transport, loading, and unloading, you can actually grasp the situation of the incoming valves, the incoming valves do not match the order contract, shortage of quantity, specification model errors, the appearance of obvious quality problems, etc., can be timely to the supplier to reject, return, and Timely contact with the procurement department to deal with the problem as soon as possible. In addition, acceptance can also create the conditions for the correct classification of valve materials for storage and correct use.

2. Acceptance inspection content and requirements

2.1 Acceptance inspection content

Valve material acceptance includes packaging, signs, appearance quality, specifications, quantity, and other aspects. Therefore, the acceptance of valve materials to do: the order/delivery list and the physical consistency; packaging, signs in line with standard regulations; good quality appearance, and accurate quantity.

2.2 Preliminary work before acceptance

Verification of documents: documents mainly order/delivery list, product certification, special valves need to be accompanied by inspection reports or production pressure piping, fire equipment special license. Before acceptance, you need to check whether the documents are complete and correct.

Check the mark: check the packaging, and signs, to see if the specifications are shown on the shipping list, the number of consistent, after checking if found to be inconsistent, shall not be accepted, such as the case is unclear, the need to contact the purchaser, with the clarification of the situation before making acceptance or rejection and other corresponding processing, the specific details of the issue can be marked in detail on the receipt list (receipt).

Prepare the location: where the valve materials into the warehouse, are based on the arrival of the number of materials, name, specifications, etc., to determine the location in the warehouse should be stored, such as a large number of loading and unloading manpower can be arranged in advance.

Acceptance tools: for the acceptance of valve materials mainly take the naked eye observation method, if necessary, can carry a measuring tape and weighing tools.

2.3. Acceptance problems in handling

Incomplete or non-conforming documents of the arriving valves must be detailed in the arrival list/receipt, and promptly notify the Purchasing Department, urging suppliers to complete the relevant documents as soon as possible. The actual situation will be recorded in the arrival records.

Quantity discrepancy: If the actual quantity is less than the quantity in the delivery list, sign the receipt and register the arrival record according to the actual quantity, and at the same time notify the purchasing department and urge the supplier to make up the missing materials as soon as possible. If the actual quantity is more than the quantity in the delivery list, the actually planned quantity of the material to be delivered can be implemented with the Purchasing Department, and if it is really more than that, the supplier will be informed to return the extra material and sign the receipt and register the arrival record according to the actual quantity received.

Wrong specifications and models: the actual situation should be notified to the Purchasing Department, if it is indeed the supplier’s loading error, then the supplier can be rejected and made to replace the correct specifications. If other problems need to be clarified, they can be treated as materials to be inspected and marked in detail on the receipt and arrival records, and wait for the problem to be solved before re-inspection and storage or rejection.

Unqualified appearance quality: should first be by this standard later for the acceptance of the valve material appearance quality description, determine whether the appearance of the material is acceptable surface defects, such as the appearance of serious quality failure, the supplier can be required to return for replacement, and the failure/degree of damage to make records, submitted to the procurement department, together with the supply unit to deal with.

Where the valve is to be accepted, the warehouse should be properly stored, stored separately, according to the provisions of the record, mark, to be processed after the problem, according to the actual situation of acceptance into the warehouse or refusal to accept the return.

3. Inspection project requirements

3.1 Packaging inspection

Packaging purpose

Packaging is to facilitate the transportation, handling, and storage of larger quantities of valve materials, to prevent damage to the form and value of the valve in circulation, the valve is placed within the form of packaging. The packaging design should be based on the characteristics of the material, and circulation conditions, to achieve compact packaging, reasonable protection, safe, and reliability.

Packaging specific requirements

Small-diameter valves of common materials packaging: most of the bag or bare form, to ensure the convenience of checking the number of acceptance, packaging bags usually do not need to be tightly sealed, due to the valve body surface oil anti-rust paint, small quantities of valves stored in the warehouse are usually bare, or a certain number of small-diameter valves in the bag, the number of bags need to be prominently displayed in the bag, specifications, and models. The bag must be firm and durable to prevent collision damage to the valve in the process of transportation.

DN300 large-diameter valves and degreasing valves and other special materials packaging: usually using wooden box packaging method, requiring solid wood, neatly arranged, no distortion, loose phenomenon. If necessary, the wooden box should be filled with another packaging to play the role of local protection.

Other details of the shipment requirements

The valve should have been factory inspected before arriving at the warehouse, after inspection should be removed from the surface of the oil and dirt, and the inner cavity should be removed from the residual experimental media.

Ball valve and plug valve opening and closing pieces should be in the open position, non-metallic material resilient seal butterfly valve butterfly plate should be opened at a small angle, check valve opening and closing pieces should be in the closed position fixed, other valve opening and closing pieces should be in the closed position.

Exposed parts such as the valve stem should be protected.

3.2 Logo inspection

A valve material mark is in the valve body surface or packaging with text/graphics/letters, etc. to indicate the characteristics of the mark, the valve mark is mainly to indicate the manufacturer, nominal pressure, nominal diameter, etc… Commonly used signs have a variety of seals/tags.

Valve sign inspection, first of all, should be identified on the valve body or sign whether there is a sign; secondly, the integrity of the sign should be checked, and the sign on the valve body should include the nominal diameter (DN), nominal pressure (PN), the material code of the pressurized parts (the above three information are available valve national standard specifications, such as J11T-16-25), the manufacturer’s name or trademark. Other information such as media flow arrows, seal ring code, limit temperature, manufacturer’s number, standard number, quality, and inspection marks are optional signs, or may not be marked on the valve body or plate. Again, the valve specifications shown on the sign should be checked to see if the delivery list matches, but also check whether the sign is intact, there is no damage lost, or unclear handwriting.

Specification inspection

Specifications and models should be included in the sign inspection and product certification inspection, and the specifications and models shown on the shipping list should be checked against the specifications and models written in the valve body or sign on the label.

Product certification should include the following: manufacturer’s name and factory date, product name and model, nominal pressure, nominal diameter, use of media and temperature, based on the standard and test date, factory number, the inspector’s seal, and so on. Product certification is not only a part of the data review but also a reference basis for specification inspection.

3.4 Quantitative inspection

Quantity inspection is an important part of the physical acceptance of the valve, the number of valves in the warehouse inspection, is to identify the number of valves in the batch of arrival and the number filled in the list submitted by the supplier is consistent. Inspection of the number of valves usually uses the method of acceptance of the point pieces.

3.5 Appearance inspection

Valve in the production process improper operation or improper handling in the transportation process, may produce defects in its surface, according to the size of these defects on the use of the valve, the rating of the appearance of defects are different, according to the national machinery industry standard JB/T7927-1999, the valve, flanges, fittings and other pressure-cast steel parts of the type of surface defects with a picture of the way ABCDE rating, defects are very minor, in the valve body surface involves a small area, in the valve manufacturing process is unavoidable minor defects in the appearance of defects, in the acceptance without processing. If the appearance of defects is more serious, affecting the pressure capacity of the valve, belonging to the obvious improper operation during production or transportation process cracked and crashed, the supplier should be made to return the goods promptly.

Appearance inspection procedures

Valve appearance inspection and quantity inspection at the same time, while acceptance to observe the appearance of the quality of the situation, with the packaging of the valve to open the packaging, while pointing pieces of acceptance while visual inspection of the appearance. For a large number of valves, sampling inspection if the presence of defects in appearance, there should be a plan to expand the number of sampling.

Judgment of the appearance of the valve quality, there must be sufficient basis. If defects are found in the acceptance process but are accidental or very few, generally do not as a basis for processing. Acceptance of the same defects found repeatedly or a variety of defects, shall be carefully identified, make a written record, if necessary, to make photographic records, as the basis for dealing with the problem.

Inspection methods

Appearance inspection is generally observed by the naked eye, but also with the help of a magnifying glass. Inspection should strictly comply with the operating procedures to avoid new appearance defects.

Identification and identification of defects in appearance

Valve appearance defects are divided into about 12 kinds, to understand the type of surface defects and the formation of the way, will help in the acceptance process to identify the different types of surface defects, according to their degree of severity, to make the appropriate treatment.

  • A. Crack: due to the role of internal and external stress, the surface of the cast steel parts appear linear cracking. Usually, obviously visible surface cracks are not qualified.
  • B. Shrinkage: due to metal shrinkage, the cast steel parts in the pouring, riser cut at the presence of extremely irregular shape, hole wall rough and with branching crystalline holes.
  • C. sand (slag) eye: due to sand particles involved in molten metal, the formation of holes with sand particles (slag) on the surface of cast steel parts.
  • D. Pore: due to the molten metal mixed with gas, and the formation of the surface of the cast steel parts of varying sizes, pear-shaped, round, oval, or needle-shaped holes in the wall is relatively smooth.
  • E. Ridge-like projection (succulent): cast steel parts on the surface of the spur (ridge) like metal projections, the shape is extremely irregular, into a network of vein-like distribution of burrs called vein pattern.
  • F. Rat tail: due to defects or deformation of the sand surface, and the formation of shallow (less than 5mm) on the surface of the cast steel parts with an acute angle of the dent.
  • G. Cold septum, crease: due to the metal is not completely fused, and in the cast steel parts formed on the surface of the rounded penetration or no penetration of the gap. The epidermis generally has deeper mesh grooves called creases.
  • H. Cutting scars: Cast steel parts in the process of cleaning, cutting pouring, and riser, due to improper correction of the scar left.
  • I. Scar: cast steel parts with scar-like metal projections on the surface, its surface is rough, with sharp edges, a small part of the metal and cast steel parts connected to the body, scar-like projections, and castings with a sand layer between.
  • J. Support scars: scars left on the surface of cast steel parts due to core support or internal cooling iron not completely melted.
  • K. Welding scars: scars left on the surface of cast steel parts due to poor post-welding corrections.
  • L. Surface roughness: The surface of cast steel parts is not smooth and uneven.

3.6 Inspection and acceptance of flange

Appearance inspection

The forging surface shall be smooth and shall not have to forge scars, cracks, and other defects.

Machined surfaces shall not have burrs, harmful scratches, and other defects that reduce the strength of the flange and the reliability of the connection.

The sealing surface of the ring connection surface flange shall be inspected in its entirety item by item, and the two sides of the groove shall not have surface defects such as cracks, scratches, or bruises caused by machining.

Quantity inspection

The flange is generally supplied with the valve set, in general, a flange connection mode of the valve with two flanges and the corresponding bolts, do the number of valves when the inspection, the number of flange inspection should be carried out at the same time. After the inspection is correct the set as a unit to sign the receipt and register the receipt ledger.

Logo

In addition to the overall flange, each flange (including the flange cover) should be made on the outer cylindrical surface of the following signs.

Manufacturer’s trademark, material grade, nominal pressure PN and nominal diameter DN.

Valve supply requirements

General requirements

  • (1) The valve must be manufactured according to its corresponding technical standards, design drawings, technical documents, and the provisions of the procurement contract. And after passing the inspection, before delivery.
  • (2) When there are special requirements, should be stipulated in the procurement contract, and should be inspected and supplied by the requirements.

Coating

  • (1) In addition to austenitic stainless steel and copper valves, other metal valves should be painted or coated according to the provisions of the contract on the non-machined external surface.
  • (2) Non-painted or no rust-proof layer of the processing surface, must be coated with easy to remove rust inhibitor. The valve cavity and parts shall not be painted and should be free of dirt and rust spots.

Logo

  • (1) The valve should have a clear logo and comply with the provisions of international standards.
  • (2) The sign should be firmly fixed in the obvious parts of the valve, its content must be complete, and correct, and should comply with the provisions of international standards, and the material should be made of stainless steel, copper alloy, or aluminum alloy.

Product quality of the valve documentation content

  • (1) The name of the manufacturer and the date of delivery.
  • (2) Product name, model, and specification.
  • (3) Nominal pressure, nominal diameter, applicable media, and applicable temperature.
  • (4) The design requirements to do the test valve, the manufacturer should be qualified to test the certificate.

Storage of valves

Valve storage

  • (1) The valve in and out of the warehouse, should be registered by the main content of the nameplate, the establishment of accounts. Test qualified valves should be made to test records and markings.
  • (2) Valves should be placed in indoor storage, and according to the specifications of the valve, model, and material are placed in storage. Department of iron contamination allowed non-ferrous metal valves and ultra-low carbon stainless steel valves, placed, storage, and protective measures should be taken.
  • (3) Return to storage valves, should be re-registered. Shell pressure test and sealing test after the valve, idle time of more than six months should be re-tested.
  • (4) The valve in the storage process, the rigging shall not be directly bolted to the handwheel or the valve upside down.

Protection of the valve

  • (1) The exposed parts of the valve stem, should be coated with grease for protection.
  • (2) In addition to plastic and rubber sealing surface is not allowed to apply rust inhibitor, the valve’s other closed parts and seat sealing surface should be coated with industrial anti-rust grease.
  • (3) The valve cavity, flange sealing surface, and bolt threads should be coated with rust inhibitor for protection.
  • (4) After the valve test, the internal should be cleaned up, and the valve ends should be added to the protective cover.

Valve data management

  • (1) The quality of documentation provided by the manufacturer, should correspond to the physical, account management.
  • (2) Check and test qualified valves, test department issued material re-inspection report, valve test records and safety valve tuning test records, and other documents, and should be signed by the relevant personnel.

Common assembly methods for valves

The valve assembly is the final stage in the production process. The valve assembly is based on the premise of the delineated skills, the various parts of the valve, parts together so that it becomes a product over ……

The whole machine is the most basic unit of the valve assembly, several parts make up the parts of the valve (such as the valve cover, valve parts, etc.). The assembly process of several parts to make up the components is called a component assembly, and the assembly process of several parts and components to make up the valve is called total assembly. Assembly work has a great impact on product quality, even if the design is accurate, and parts qualified, if improperly assembled, the valve will not meet the specified requirements, and even produce sealing leakage. Therefore, special attention should be paid to the use of fair assembly methods to ensure the quality of the final product of the valve. In production, the form of documents delineating the assembly process is called assembly process procedures.

Valve assembly methods commonly used can be three, namely the complete interchange method, repair method, and optional method.

1. Complete interchange method

Valve assembly using the complete interchange method, each part of the valve does not have to go through any repair and selection can be assembled, the product after assembly that can meet the specified technical requirements. At this point, the valve parts are to be processed in full accordance with the design requirements, to meet the requirements of dimensional accuracy and shape tolerance. The advantages of the complete interchange method are: assembly work is simple and economic, workers do not need a high degree of skill, the production efficiency of the assembly process is high, easy to organize assembly lines, and the organization of specialized production. However, in absolute terms, take a complete swap assembly, the parts of the processing accuracy requirements are higher. Practical for globe valves, check valves, ball valves, and other valves with an absolutely simple structure, as well as medium and small diameter valves.

2. Optional method

Valve to adopt the optional method of assembly, the whole machine can be processed according to the economic precision, assembly, and then a certain adjustment, compensation effect of the size of the optional to reach the specified assembly accuracy. The principle of the optional method is the same as the repair method, only the way to change the size of the compensation ring is different. The former is to use the method of selecting accessories to change the size of the compensation ring, and the latter is to use the method of repairing accessories to change the size of the compensation ring. For example the control valve model double gate wedge gate valve top core and transfer gasket, the transfer gasket between the two bodies of the foliate ball valve, etc., to take special parts in the size chain related to the assembly accuracy as compensation parts, by adjusting the thickness of the gasket size, to reach the required assembly accuracy. To ensure that in different situations can be fixed compensation parts for optional, it is necessary to pre-manufacture a set of different thickness sizes of gaskets, bushings compensation parts hydraulic control valve models for assembly selection.

3. Repair method

Valve assembly using the repair method, parts can be processed according to economic precision, assembly and then a certain adjustment, make up for the effectiveness of the size of the repair, to achieve the specified assembly goals. Such as the wedge gate valve gate and body, because the processing cost to achieve interchangeable requirements is too high, most manufacturers are using the repair method process. That is, in the final grinding of the gate sealing surface control the open file size and body sealing surface of the open file size to match the way to match the plate, to achieve the ultimate sealing requirements. This method certainly adds to the plating process, but greatly simplifies the dimensional accuracy requirements of the front processing process, with the plating process being purely operated by a dedicated person, and overall does not affect the effectiveness of production. Valve assembly process: valve individual fixed-site assembly, valve parts, and components assembly, and total assembly is carried out in the assembly plant, and the required parts and components are all transported to the assembly workplace. Usually, parts assembly and total assembly are distinguished by the number of groups of workers at the same time, which not only shortens the assembly cycle but also facilitates the application of special assembly tools, the requirements of the technical level of workers are also relatively low.

Some foreign manufacturers or high technology grade valves also have the mode of assembly suspension line or assembly rotary table.

1. Assembly before the preparatory work

Valve parts in the assembly before the need to remove the burrs and welding residues of mechanical processing residue, cleaning and cutting packing and gaskets.

2. Cleaning of valve parts

As a fluid pipeline control installation of the valve, the inner cavity must be clean. In particular, in nuclear power, medicine, and food industry valves, to protect the purity of the medium and avoid media contamination, the requirements of the valve cavity cleanliness are more stringent. Before assembly should answer the valve parts for cleaning, the parts on the chipping debris, residual smooth oil, coolant and burrs, welding slag, and the rest of the dirt wash away clean. Valve cleaning usually with alkaline water or hot water spray brush (also available kerosene for scrubbing) or in the ultrasonic cleaning machine cleaning. Parts by grinding, polishing after the final cleaning, the final cleaning is usually the sealing surface parts with gasoline brush clean, and then blow dry with compressed air and wipe clean with a cloth.

3. Packing and gasket preparation

Graphite packing is commonly used because of the advantages of corrosion resistance, good sealing, and a small coefficient of friction. The packing and gasket are used to prevent the medium from leaking through the valve stem and bonnet and between the joint surfaces of the flange. These accessories are to be ready for cutting and receiving before the assembly of the valve.

4. Valve assembly

Valve is usually the valve body as a benchmark part by the order and methods of assembly of the process. Before assembly review the parts and components, to avoid not deburred and not cleaned parts into the general assembly. Assembly process, parts should be lightly held and placed to avoid bumping and scratching processors. The moving parts of the valve (such as the stem, bearings, etc.) should be coated with industrial grease. Valve cover and valve body flange more bolt connection, fastening bolts, should be proportional, intertwined, repeated, average tightening, otherwise the valve body, the joint surface of the valve cover will be unevenly around the force and the flow control valve leakage. Tightening when using the hand should not be too long to prevent excessive preload and affect the strength of the bolt. The pre-tightening force has a strict request for the valve, which should be applied to the torque hand, according to the specified torque requirements lemon tighten the bolt. After the total assembly, should rotate the holding mechanism, to check whether the valve opening and closing activities are mobile, there is no card blocking the scene. Pressure-reducing valve cover, bracket, and other parts of the installation direction are in line with the requirements of the drawings, the review is qualified after the valve can only be tested.

Valve operation precautions and installation and disassembly maintenance

A. Notes on the operation of the valve.

Valve is an important part of the thermal system, operating personnel often have to deal with the valve, so you must be familiar with the structure of the valve to master the performance, correct identification of the valve direction, opening signs, indication signals, should be able to skillfully and accurately adjust and operate the valve in a timely and decisive manner to deal with various emergency failures. When operating the main attention to the following categories.

  • 1. Identify the direction of the valve switch. In general manual valve, the handwheel clockwise direction of rotation indicates the direction of valve closure, counterclockwise direction indicates the direction of valve opening, there are individual valve directions and the opposite of the above opening and closing, should check the opening and closing signs before the operation, the top surface of the plug valve stem groove and channel parallel, marking the valve in the fully open position, when the stem rotates 90. groove and channel vertical, marking the valve in the fully closed Position, some plug valves with a wrench parallel to the channel for open, vertical for closed. Three-way, four-way valve operation should be opened and closed by the commutation mark.
  • 2. Force to be appropriate, the operation of the valve, too much force is easy to damage the handle, hand wheel, bruise the stem and sealing surface, and even crush the sealing surface, do not use a large wrench to open and close the small valve to prevent excessive force, damage to the valve.
  • 3. Before opening the steam valve, you must first preheat the pipeline to exclude condensate, and open it slowly to avoid the phenomenon of water hammer and damage to valves and equipment.

Larger diameter valves with bypass valves, open inches, should first open the bypass valve, to reduce the pressure difference between the two sides of the valve, and then open the large valve. Close the valve, first close the bypass valve, and then close the valve.

Gate valve, globe valve type valve open to the head, to turn 1/4-1/2 turn, conducive to the operation of the check, so as not to screw too tightly, damaging the valve parts.

B. The common failure of the valve.

  • 1. Media leakage: due to the valve inlet and outlet flange, valve cover, stem seal at the packing damage, and valve body with sand eyes, cracks, etc., generally need to repair professionals to deal with.
  • 2. The valve is not closed tightly. The reason is that the valve is not closed to the end, the sealing surface of debris, the solution is: check whether the valve opening in the fully closed position, or open the valve again after a few turns to close tight, there is a seal surface blowing damage, the need for maintenance personnel to repair.
  • 3. Valve switch does not move, the reason is that the valve is too tight or open too large, this inch should first check and analyze the state of the valve, do not blindly excessive force to operate, to prevent damage to the valve, such as valve card rust to try to repair.
  • 4. Valve spool off. Damage to the stem nut will cause the valve to open and close abnormal, such as the bright stem valve stem rotation, the valve switch does not end, etc., the operator should analyze and judge by experience.
  • 5. Transmission mechanism failure. Electric, and hydraulic valve transmission mechanism parts damage will also make the valve can not be opened and closed normally. At this time should repair the transmission device.

C. How to disassemble the valve.

  • 1. The surface will be clean.
  • 2. Mark the valve body and valve cover, and then open the valve.
  • 3. Remove the transmission device or remove the hand wheel nut, take the hand wheel.
  • 4. Remove the glen screw, back off the glen, and take off the packing.
  • 5. Check down the door cover nut and door cover and gasket.
  • 6. Spin out the valve stem and take off the valve spool.
  • 7. Remove the screws, and nuts lee plain bearings, and put all the parts in place.

D. The valve assembly steps.

  • 1. Grease the plane bearing, together with the screw sleeve into the bearing seat on the valve cover bracket.
  • 2. Install the valve flap on the valve plate and tighten the lock nut or connecting nut.
  • 3. Put the valve stem into the packing box, then put on the packing bottom ring gland, screw in the screw sleeve plants, to the open position.
  • 4. Clean the valve body and valve flap.
  • 5. Install the gasket between the flange Z of the valve body and the valve cover, and then snap the assembled valve cover onto the valve body correctly.
  • 6. Tighten the bolts symmetrically and evenly, and the flange should not be skewed.
  • 7. Add packing as required.
  • 8. Conduct hydraulic tests.

E. Replace the valve packing

Operation steps and methods.

  • 1. Select packing according to the specification of the valve, the medium, temperature, and pressure used.
  • 2. Clean the valve packing chamber.
  • 3. Check and measure the packing bottom ring and the valve stem clearance, the outer circle of the gran and the packing box, the gran hole, and the valve stem clearance. If the gap does not meet the requirements, it should be adjusted.
  • 4. Add packing.
  • 5. Fasten the bolt.

The correct method of operation of the valve and precautions

For the valve, not only to be installed and maintained but also to operate. A. Manual valve opening and closing.

  • 1. Manual valve is the most widely used valve, its hand wheel or handle, is designed by ordinary human power, taking into account the strength of the seal smell and the necessary closing force. Therefore, you cannot use a long lever or a long plate hand to plate the movement. Some people are accustomed to using the plate hand, should be strictly noted plate, do not use too much force, otherwise, it is easy to damage the sealing surface or plate broken hand wheel, handle.
  • 2. Open and close the valve, the force should be smooth, not impact. Some impact opening and closing of the high-pressure valve components have been considered this impact force and general valve can not be equal to Gon.
  • 3. For the steam valve, open before, should be pre-heated, and push out the condensate, open, should be as slow as possible to avoid the phenomenon of water strike.
  • 4. When the valve is fully open, the handwheel should be reversed a little, so that the thread between the tight, so as not to loosen the damage. For the open stem valve, remember the position of the stem when fully open and fully closed to avoid hitting the dead center when fully open. And it is easy to check whether it is normal when fully closed. If the valve office off, or the spool seal between the fade into the larger debris, the fully closed stem position changes.
  • 5. When the pipeline is first used, more internal dirt, the valve can be slightly open, the use of the high-speed flow of media, will be washed away, and then gently closed (not fast closed, closed, to prevent residual impurities pinch sealing surface), open again, so repeat many times, flush clean dirt, and then put into normal operation.
  • 6. Often open the valve, the sealing surface may be sticky dirt, close the above method should also be used to flush it clean, and then formally close the tight.
  • 7. Such as handwheels, handles damaged or lost, should be immediately equipped, do not use the live plate hand instead, so as not to damage the valve stem quadrilateral, opening and closing do not work, resulting in accidents in production.
  • 8. Certain media, cooling after the valve is closed, so that the valve shrinkage, the operator should be closed again at the appropriate time – a time, so that the seal without leaving a slit, otherwise, the media from the slit flowing at high speed, it is easy to erode the seal and.
  • 9. Operation, such as the operation is found to be too much effort, should analyze the reasons. If the packing is too tight and can be properly relaxed, such as if the valve stem is skewed, should notify the personnel repair. Some valves, in the closed state, the closing piece of thermal expansion, resulting in opening difficulties; such as must be opened at this time, the valve cover threads can be loosened half a turn to – turn, eliminate the stem stress, and then plate hand wheel.

Note:

  • 1. More than 200 ° C high-temperature valves, due to installation at room temperature, and after normal use, the temperature rises, the bolt heat expansion, the gap increases, so it must be tightened again, called “hot tight”, the operator should pay attention to this – work, otherwise it is easy to leak
  • 2. In Cold weather, the water valve is closed for a long time to stop, the valve should be removed after the water. Steam valve after stopping steam, but also to exclude condensate. The bottom of the valve has a silk plug, it can be opened to drain.
  • 3. Non-metallic valves, some hard and brittle, some lower strength, operation, open and close the force can not be too people, especially not to make a strong. Also, pay attention to prevent objects from bumping.
  • 4. In The new valve, the packing should not be pressed too tightly to not leak, so as not to pressure the stem too much, accelerate wear and tear, and opening and closing effort.

Daily maintenance of the valve

1. The valve should be stored in a dry and ventilated room, and both ends of the pathway must be blocked.

2. Long-term storage of valves should be regularly inspected, remove dirt, and rust-proof oil on the processing surface.

3. After installation, should be regularly inspected, the main inspection items.

  • (1) The seal surface wear.
  • (2) The wear of the trapezoidal thread of the stem and stem nut.
  • (3) Whether the packing is out of date or failed if there is damage should be replaced promptly.
  • (4) Valve maintenance and assembly, sealing performance test should be conducted.

For the valve in operation, a variety of valve parts should be complete and intact. The flange and bracket on the bolt can not be missing, the thread should be intact, and no loose phenomenon is allowed. The fastening nut on the handwheel, if found loose, should be tightened in time to avoid wear of the connection or loss of the handwheel and the nameplate. If the handwheel is lost, it is not allowed to replace with a live wrench, and it should be matched in time. The packing gland is not allowed to be skewed or have no pre-tightening gap. For valves in an environment susceptible to rain, snow, dust, sand, and other dirt stains, the stem should be installed to protect the cover. The scale on the valve should be kept intact, accurate, and clear. Valve seals, caps, pneumatic accessories, etc. should be complete and intact. The insulation jacket should be free of dents and cracks. Do not allow knocking, standing people, or supporting heavy objects on the running valve; especially non-metallic valves and cast iron valves, more prohibit.

(A) Custody maintenance

The purpose of custodial maintenance is to keep the valve from being damaged in storage or reducing the quality. In fact, improper storage is one of the important reasons for damage to the valve. Valve storage should be well organized, small valves on the shelves, large valves can be neatly arranged on the ground in the warehouse, can not be stacked in a mess, and do not let the flange connection surface contact the ground. This is not only for the sake of aesthetics, but mainly to protect the valve does not touch bad. Due to improper storage and handling, the handwheel is broken, the valve stem crooked, the handwheel and the stem of the fixed nut lose lost, etc., these unnecessary losses should be avoided. For valves that are not used for a short period of time, asbestos packing should be taken out to avoid electrochemical corrosion and damage to the stem. The valve just into the warehouse, to check, such as in the process of transportation into the rain or dirt, to wipe clean, and then to store. Valve import and export should be sealed with wax paper or plastic sheet to prevent the entry of dirty things. Can rust in the atmosphere of the valve processing surface to be coated with anti-rust oil, to protect. Valves placed outdoors, must be covered with linoleum or sheeting and other rainproof, dustproof items. The warehouse where the valve is stored should be kept clean and dry.

(B) The use of maintenance

The purpose of use and maintenance is to extend the life of the valve and ensure reliable opening and closing. Stem threads, often friction with the stem nut, to apply a little yellow dry oil, molybdenum disulfide, or graphite powder, to play a role in lubrication. Infrequent opening and closing of the valve, but also regularly turn the handwheel to add lubricant to the stem threads to prevent a bite. Outdoor valves, to add a protective sleeve for the stem to prevent rain, snow, dust, and rust stains. If the valve is mechanical to be moved, add lubricant to the gearbox on time.

(C) The maintenance of the valve in the operation

1. Cleaning

The surface of the valve, stem, and stem nut on the trapezoidal thread, stem nut and bracket sliding parts and gears, worm gear and other components, easy to accumulate a lot of dust, oil, and media residue and other spoils, the valve will produce wear and corrosion. Therefore, it is obviously important to keep the external and moving parts of the valve clean and protect the integrity of the valve paint. The dust on the valve is suitable for brush sweeping and compressed air blowing; the trapezoidal threads and the dirt between the teeth are suitable for rag scrubbing; the oil and residue on the valve are suitable for steam blowing and even brushing with copper wire until the processing surface and the matching surface show the metallic luster and the paint surface shows the original color of the paint. The trap should be responsible for at least one inspection per shift, and regularly open the flushing valve and the plug at the bottom of the trap to flush, or regularly disassemble and flush, so as not to block the valve with stolen goods.

2. Lubrication of the valve

Valve trapezoidal thread, stem nut, bracket sliding parts, bearing parts, gears and worm gear, worm gear meshing parts, and others with active parts, need good lubrication conditions, reduce mutual friction, to avoid mutual wear. Some parts are specially equipped with oil cups or oil nozzles, if damaged or lost in operation, should be repaired to match, the oil circuit to unclog. Lubrication parts should be regularly refueled according to specific circumstances. Often open, high-temperature valves are suitable for a week to a month between refueling; not often open, not high-temperature valve refueling cycle can be longer. Lubricants such as oil, grease, molybdenum disulfide, and graphite. High-temperature valves are not suitable for oil, or grease, they will be lost due to high-temperature melting, and are suitable for injection of molybdenum disulfide and wipe graphite powder. The exposed parts need to be lubricated, such as trapezoidal threads, gears, and other parts, if butter and other greases, easy to stain the dust, while the use of molybdenum disulfide and graphite powder lubrication, it is not easy to stain the dust, lubrication effect than the yellow good. Graphite powder is not easy to apply directly, a little oil or water can be used as a paste. Oil injected sealed plug valve should be oiled by the prescribed time, otherwise, it is easy to wear and leak.

Valve grease maintenance

Before welding and after the commissioning of the valve professional maintenance work for the valve to serve the production operation plays a vital role, correct and orderly, and effective maintenance will protect the valve, so that the valve normal function and extend the service life of the valve. Valve maintenance work seems simple, but it is not. There are often overlooked aspects of the work.

  • First, the valve greasing often ignores the amount of grease injection. After the grease gun is refueled, the operator selects the valve and the grease linkage and then carries out the grease filling operation. There are two situations: on the one hand, the amount of grease injection is not enough, and the sealing surface will be worn out faster due to the lack of lubricant. On the other hand, too much grease is injected, resulting in waste. The problem is that there is no accurate calculation of the sealing capacity of different valves according to the type of valves. The sealing capacity can be calculated by the valve size and category, and then the appropriate amount of grease can be injected reasonably.
  • Secondly, the pressure problem is often ignored when greasing the valve. During the grease injection operation, the grease injection pressure changes regularly in peaks and valleys. If the pressure is too low, the seal will leak or fail, and if the pressure is too high, the grease injection port will be blocked, the seal will be hardened or the seal will be blocked with the valve ball and valve plate. Usually, when the grease injection pressure is too low, the injected grease will flow into the bottom of the valve cavity, which usually happens in small gate valves. If the grease injection pressure is too high, on the one hand, check the grease injection nozzle, if the grease hole is blocked, identify the situation and replace it; on the other hand, if the grease is hardened, use a cleaning solution to soften the failed seal grease repeatedly and inject new grease for replacement. In addition, the seal type and seal material also affect the grease injection pressure, different seal forms have different grease injection pressure, in general, the hard seal grease injection pressure is higher than the soft seal.
  • Third, when greasing the valve, pay attention to the valve in the switch position. Ball valve maintenance is generally in the open position, and in special cases, choose to close the maintenance. Other valves can not be generalized to the open position. Gate valve in maintenance must be in the closed state, to ensure that the grease along the seal ring is full of sealing grooves, if the open position, sealing grease is directly into the flow channel or valve cavity, resulting in waste.
  • Fourth, the valve grease injection often ignores the effect of the grease injection problem. In the operation of grease injection, the pressure, the amount of grease injection, and the switch position are normal. However, to ensure the effect of valve greasing, it is sometimes necessary to open or close the valve to check the lubrication effect and confirm that the valve ball or gate surface is evenly lubricated.
  • Fifth, grease injection, pay attention to the valve body drainage and silk plug pressure relief problems. After the valve pressure test, the gas and moisture in the seal cavity valve cavity will be pressurized due to the rise of ambient temperature, and the drainage and pressure relief should be carried out first when injecting grease to facilitate the smooth operation of grease injection. The air and moisture in the sealing cavity are fully replaced after grease injection. The pressure in the valve cavity is relieved in time, which also ensures the safety of the valve. After grease filling, be sure to tighten the drainage and pressure relief plug to prevent accidents.
  • Sixth, when filling grease, pay attention to the problem of uniform grease output. In normal greasing, the grease hole nearest to the grease injection port will be greased first, then to the low point, and finally to the high point, one by one. If the grease does not come out according to the law or does not come out, it proves that there is a blockage, so timely clearing and processing.
  • Seventh, grease injection should also be observed when the valve diameter and seal seat flush problem. For example, in the ball valve, if there is an open position overfill, you can adjust the open position limiter inward to confirm the passage diameter flush and then lock. Adjustment limit can not only pursue open or close a party position, to consider the overall. If the open position is flush and not in place, the valve will not close tightly. Similarly, adjust the off in place, but also consider the corresponding adjustment of the open position. Ensure that the right-angle stroke of the valve.
  • Eighth, after greasing, be sure to seal the grease injection port. Avoid the entry of impurities or grease oxidation at the grease injection port, and the cover should be coated with anti-rust grease to avoid rusting. So that the next operation is applied.
  • Ninth, when filling grease, also consider the specific problems in the future oil sequential transport specific treatment. Given the different qualities of diesel and gasoline, the flushing and decomposition ability of gasoline should be considered. In the future valve operation, encounter gasoline section operation, timely replenishment of grease to prevent wear and tear situation.
  • Tenth, when greasing, do not ignore the greasing of the valve stem part. Valve shaft parts have sliding bushings or packing, and also need to maintain a lubricated state to reduce the frictional resistance during operation, such as failure to ensure lubrication, the torque increases wear parts during electric operation, and manual operation when the switch is laborious.
  • Eleventh, some ball valves are marked with arrows on the valve body, if not accompanied by the English FIOW words, the direction of action of the seal seat, not as a reference to the media flow, the valve self-discharge direction in the opposite direction. Usually, double-seated sealed ball valves have a two-way flow direction.
  • Twelfth, the valve maintenance, also pays attention to the electric head and its transmission mechanism in the water into the problem. Especially in the rainy season infiltration of rainwater. One is to make the transmission mechanism or transmission sleeve rust, the second is frozen in winter. Causes excessive torque when operating the electric valve, damage to the transmission parts will make the motor no-load or over-torque protection jump open can not achieve electric operation. Damage to the transmission parts, and manual operation is also impossible. In the over-torque protection action, manual operation is also the same and can not switch, such as forced operation, which will damage the internal alloy parts.

How to solve the valve sealing surface damage? 

Seal surface damage may be man-made damage or natural damage for two reasons. Man-made damage is caused by poor design, poor manufacturing, improper material selection, improper installation, bad use, poor maintenance, etc. Natural damage, is the normal working conditions of the valve wear, is the media on the sealing surface of the inevitable corrosion and erosion caused by damage.

Specifically, the valve sealing surface damage may also be caused by the following reasons.

  • First, improper selection and poor manipulation are caused by damage. Performance in the premise of the selection of valves according to the working conditions, the cut-off valve as a throttle valve, resulting in the closure of the pressure is too large and closed too quickly or closed not tight, so that the sealing surface erosion and wear.
  • Second, is the sealing surface processing quality problems. Seal surface cracks, porosity, and defects such as ballast, because of improper selection of overlay welding and heat treatment specifications and overlay welding and heat treatment process caused by poor manipulation, seal surface hardness is too high or too low, because of the wrong material selection or improper heat treatment caused by the seal surface hardness is not uniform, not resistant to erosion, mainly because in the process of overlay welding the bottom layer of metal blown to the top, diluted the sealing surface alloy composition caused by The, Of course, there is also the design of the subject.
  • Third, mechanical damage, the sealing surface in the process of opening and closing will produce abrasions, bruises, extrusion, and other damage. Between the two sealing surfaces, under the action of high temperature and pressure, the atoms penetrate and exude each other, resulting in adhesion. When the two sealing surfaces move to each other, the adhesion is easily pulled apart. The higher the surface roughness of the sealing surface, the more easily this phenomenon occurs. Valve in the process of closure, valve flap in the process of returning to the seat will touch and squeeze the sealing surface so that the sealing surface local wear or indentation.
  • Fourth, is electrochemical corrosion. Is the result of media activity on the sealing surface wear, flushing, and vapor corrosion. Media at a certain speed, the media in the floating fines touch offensive sealing surface so that it causes local damage, the high-speed activity of the media directly wash the sealing surface, so that it causes local damage, media mixing, and local vaporization, the production of gas angry bubble blast impact sealing surface, resulting in local damage. Media erosion coupled with chemical erosion alternating effects will strongly leach the sealing surface.
  • Fifth is the medium of chemical erosion. Seal surface near the media in the case of non-current generation, the media directly with the seal surface chemical action, erosion of the sealing surface.
  • Sixth, the media erosion. It is the result of media activity on the sealing surface wear, flushing, and cavitation. Media at a certain speed, the media in the floating fines touch the sealing surface, so that it causes local damage, the high-speed activity of the media directly wash the sealing surface, so that it causes local damage, media mixing and local vaporization, the production of gas angry bubble blasting impact on the sealing surface, causing local damage. Media erosion coupled with chemical erosion alternating effects will strongly leach the sealing surface.
  • Seventh, improper installation and maintenance of the sealing surface do not work properly. Valve running with disease premature damage to the sealing surface.

Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.sfutube.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Stainless Steel Valves, Stainless Steel Flanges, Stainless Steel Pipe Fittings, and Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels, and other industries.)

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