Contraindications during valve installation

Installation of valves

Many valves have directionality, such as stop valve, throttle valve, pressure reducing valve, check valve, etc. if installed upside down, it will affect the service effect and service life (such as throttle valve), or it will not work at all (such as pressure reducing valve), or even cause danger (such as check valve). For general valves, there are direction marks on the valve body; If not, it shall be correctly identified according to the working principle of the valve. The valve cavity of the stop valve is asymmetric from left to right. The fluid should pass through the valve port from bottom to top, so that the fluid resistance is small (determined by the shape), the opening is labor-saving (due to the upward pressure of the medium), and the medium does not press the packing after closing, which is convenient for maintenance. This is the reason why the stop valve cannot be reversed. Other valves also have their own characteristics.

contraindications during valve installation - Contraindications during valve installation

Valve installation position

The installation position of the valve must be convenient for operation: even if the installation is temporarily difficult, it should also be considered for the long-term work of the operator. It is best to align the valve handwheel with the chest (generally 1.2m away from the operating floor). In this way, it is easier to open and close the valve. Do not tilt the hand wheel upward to avoid landing. For the valves near the wall machine and equipment, the room for the operator to stand shall also be reserved. It is necessary to avoid upward operation, especially acid-base and toxic media, otherwise it is very unsafe. Do not install the gate upside down (i.e. the hand wheel is downward), otherwise the medium will remain in the bonnet space for a long time, which is easy to corrode the valve stem, and it is contraindicated by some process requirements. It is very inconvenient to replace the packing at the same time. Do not install the rising stem gate valve underground, otherwise the exposed stem will be corroded due to humidity. When installing the lift check valve, ensure that its disc is vertical so that it can be lifted flexibly. When installing the swing check valve, ensure that its pin shaft is horizontal so that it can swing flexibly. The pressure reducing valve shall be installed vertically on the horizontal pipeline without tilting in all directions.

Construction operation

Care must be taken in installation and construction to avoid hitting valves made of brittle materials.
Before installation, check the valve, check the specification and model, and identify whether there is damage, especially for the valve stem. Also turn a few times to see if it is skewed, because the valve rod is most likely to be skewed during transportation. Also remove the sundries in the valve.
When lifting the valve, the rope should not be tied to the hand wheel or valve stem to avoid damaging these parts, but should be tied to the flange.
The pipeline connected to the valve must be cleaned. Compressed air can be used to blow away iron oxide chips, mud and sand, welding slag and other sundries. These sundries are not only easy to scratch the sealing surface of the valve, but also large particle sundries (such as welding slag) can block the small valve and make it ineffective. When installing the screw valve, the sealing packing (hemp with aluminum oil or PTFE raw material belt) shall be wrapped on the pipe thread and shall not be put into the valve to avoid accumulation in the valve and affect the medium flow.
When installing the flange valve, pay attention to tighten the bolts symmetrically and evenly. The valve flange and pipe flange must be parallel with reasonable clearance to avoid excessive pressure and even cracking of the valve. Pay special attention to brittle materials and valves with low strength. For the valve to be welded with the pipe, spot weld it first, then fully open the closing part, and then weld it.

Protective measures

Some valves must also have external protection, which is thermal insulation and cold insulation. Sometimes mixing hot steam pipeline is added in the insulation layer. What kind of valve should be insulated or cold should be determined according to the production requirements.
In principle, if the medium in the valve reduces the temperature too much, which will affect the production efficiency or freeze the valve, it needs heat preservation or even hot mixing; Where the valve is exposed, which is unfavorable to production or causes frosting and other adverse phenomena, it is necessary to keep cold. Thermal insulation materials include asbestos, slag wool, glass wool, perlite, diatomite, vermiculite, etc; Cold insulation materials include cork, perlite, foam, plastic and so on.

Bypass and instrumentation

Some valves, in addition to the necessary protection facilities, also have bypass and instruments. Bypass is installed. Convenient for maintenance of drain valve. Other valves are also equipped with bypass. Whether to install bypass depends on the condition, importance and production requirements of the valve.

Packing replacement

For valves in stock, some packing has been difficult to use, and some are inconsistent with the use medium, so it is necessary to replace the packing.
The valve manufacturer cannot consider using different media of thousands of units. The stuffing box is always filled with ordinary packing, but when using, the packing must adapt to the media.
When replacing the packing, press it in circle by circle. The joint of each circle should be 45 degrees, and the connection between circles should be 180 degrees. The packing height should consider the space for the gland to continue pressing. At present, the lower part of the gland should be pressed to an appropriate depth of the packing chamber, which can generally be 10-20% of the total depth of the packing chamber. For valves with high requirements, the joint angle is 30 degrees. The joints between rings are staggered by 120 degrees. In addition to the above fillers, shaped fillers such as rubber O-rings (natural rubber resistant to weak alkali below 60 ℃, nitrile rubber resistant to oil crystals below 80 ℃, and fluororubber resistant to a variety of corrosive media below 150 ℃) three piece stacked PTFE rings (resistant to strong corrosive media below 200 ℃) and nylon bowl rings (resistant to ammonia and alkali below 120 ℃) can also be used according to specific conditions. A layer of PTFE raw material belt is wrapped outside the ordinary asbestos packing, which can improve the sealing effect and reduce the electrochemical corrosion of the valve rod.
When pressing the seasoning, rotate the valve rod at the same time to keep the surrounding uniform and prevent it from being too dead. Tighten the gland evenly without tilting.

Contraindications during valve installation

Valves are the most common equipment in chemical enterprises. It seems easy to install valves, but if they are not implemented in accordance with relevant technologies, safety accidents will be caused.

Taboo 1

During winter construction, hydrostatic test shall be conducted under negative temperature.
Consequence: due to the rapid freezing in the pipe during the hydrostatic test, the pipe is frozen and damaged.
Measures: try to carry out the hydraulic test before winter construction, and blow out the water after the pressure test, especially the water in the valve must be removed, otherwise the valve will rust or freeze crack. When the hydraulic test of the project must be carried out in winter, the indoor positive temperature shall be maintained, and the water shall be blown out after the pressure test.

Taboo 2

The pipeline system is not washed carefully before completion, and the flow and speed can not meet the requirements of pipeline flushing. Even hydraulic strength test drainage is used instead of flushing.
Consequence: if the water quality fails to meet the operation requirements of the pipeline system, the pipeline section will often be reduced or blocked.
Measures: flush with the maximum design flow in the system or the water flow rate that should not be less than 3m/s. The water color and transparency of the outlet shall be consistent with that of the inlet through visual inspection.

Taboo 3

Sewage, rainwater and condensate pipes are concealed without closed water test.
Consequence: it may cause water leakage and user loss.
Measures: the closed water test shall be inspected and accepted in strict accordance with the specifications. The concealed sewage, rainwater and condensate pipes buried underground, in the ceiling and in the pipe room shall ensure no leakage.

Taboo 4

During the hydraulic strength test and tightness test of the pipeline system, only the pressure value and water level change are observed, and the leakage inspection is not enough.
Consequence: leakage occurs after the operation of the pipeline system, affecting the normal use.
Measures: when the pipeline system is tested according to the design requirements and construction specifications, in addition to recording the pressure value or water level change within the specified time, it is necessary to carefully check whether there is leakage.

Taboo 5

Butterfly valve flanges are ordinary valve flanges.
Consequence: the size of butterfly valve flange is different from that of ordinary valve flange. The inner diameter of some flanges is small, while the valve disc of butterfly valve is large, resulting in failure to open or hard opening and damage to the valve.
Measures: the flange plate shall be processed according to the actual size of the butterfly valve flange.

Taboo 6

There are no reserved holes and embedded parts in the construction of building structure, or the size of reserved holes is too small and the embedded parts are not marked.
Consequence: during the construction of heating and sanitation project, the building structure is chiseled, and even the stressed reinforcement is cut off, which affects the safety performance of the building.
Measures: carefully get familiar with the construction drawings of heating and sanitation works, actively and carefully cooperate with the construction of building structures to reserve holes and embedded parts according to the needs of the installation of pipes, supports and hangers, and refer to the design requirements and construction specifications for details.

Taboo 7

The pipeline is directly buried in frozen soil and untreated loose soil, and the spacing and position of pipeline buttress are improper, even in the form of dry brick.
Consequence: due to unstable support, the pipeline is damaged during backfill compaction, resulting in rework and repair.
Measures: the pipeline shall not be buried in frozen soil and untreated loose soil. The spacing of buttresses shall meet the requirements of construction specifications, and the supporting pad shall be firm. Especially at the pipeline interface, it shall not bear shear force. Brick buttresses shall be built with cement mortar to ensure integrity and firmness.

Taboo 8

The expansion bolt for fixing the pipe support is made of poor material, the hole diameter for installing the expansion bolt is too large, or the expansion bolt is installed on the brick wall or even the light wall.
Consequence: the pipe support is loose, and the pipe is deformed or even falls off.
Measures: qualified products must be selected for expansion bolts. If necessary, samples shall be taken for test and inspection. The hole diameter of the installed expansion bolts shall not be greater than the outer diameter of the expansion bolts by 2mm. The expansion bolts shall be applied to concrete structures.

Taboo 9

The strength of flange plate and gasket of pipeline connection is not enough, and the connecting bolt is short or the diameter is thin. Rubber gaskets are used for heat pipes, double-layer gaskets or inclined gaskets are used for cold water pipes, and flange gaskets protrude into the pipes.
Consequence: the flange connection is not tight, or even damaged, resulting in leakage. The flange gasket protrudes into the pipe, which will increase the water flow resistance.
Measures: the flange and gasket of the pipeline must meet the requirements of the design working pressure of the pipeline.
The flange gasket of heating and hot water supply pipeline should adopt rubber asbestos gasket; The flange gasket of water supply and drainage pipeline should adopt rubber gasket.
The gasket of the flange shall not protrude into the pipe, and its outer circle should reach the flange bolt hole. Inclined gasket or several gaskets shall not be placed in the middle of the flange. The bolt diameter of the connecting flange should be less than 2mm than the hole diameter of the flange plate, and the length of the bolt rod protruding from the nut should be 1 / 2 of the thickness of the nut.

Taboo 10

Wrong valve installation method.
For example, the water (steam) flow direction of stop valve or check valve is opposite to the mark, the valve stem is installed downward, the check valve installed horizontally is installed vertically, the handle of rising stem gate valve or butterfly valve has no opening and closing space, and the valve stem of concealed valve does not face the inspection door.
Consequence: the valve fails, the switch is difficult to repair, and the valve stem is downward, which often leads to water leakage.
Measures: the installation shall be carried out in strict accordance with the valve installation instructions. The rising stem gate valve shall leave enough extension and opening height of the valve stem. The rotation space of the handle shall be fully considered for the butterfly valve. The valve stems shall not be lower than the horizontal position, let alone downward. The concealed valve shall not only be provided with an inspection door to meet the opening and closing needs of the valve, but also the valve stem shall face the inspection door.

Taboo 11

The specification and model of the installed valve do not meet the design requirements.
For example, the nominal pressure of the valve is less than the system test pressure; When the diameter of water supply branch pipe is less than or equal to 50mm, gate valve shall be adopted; The main and vertical pipes of hot water heating adopt stop valves; The suction pipe of fire pump adopts butterfly valve.
Consequence: it affects the normal opening and closing of the valve and the function of adjusting resistance, pressure and so on. It even causes the valve to be damaged and forced to repair during the operation of the system.

Measures: be familiar with the application scope of various valves, and select the specification and model of valves according to the design requirements. The nominal pressure of the valve shall meet the requirements of system test pressure. According to the requirements of the construction specification: the stop valve shall be used when the diameter of the water supply branch pipe is less than or equal to 50mm; When the pipe diameter is greater than 50mm, gate valve shall be used. The dry and vertical control valves of hot water heating shall be gate valves, and the suction pipes of fire pumps shall not be butterfly valves.

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, 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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