What is a plug valve?
Plug valve is a quick opening and closing through valve. Because the movement between the rotary sealing surfaces has the function of wiping, it can completely prevent contact with the flowing medium when fully opened, so it can also be used for the medium with suspended particles. Another important feature is that it is easy to adapt to multi-channel structure, so that one valve can obtain two, three or even four different flow channels. This can simplify the design of the piping system, reduce the consumption of valves and some connecting accessories required in the equipment.
Plug valve is a kind of valve with closing part or plunger shaped rotary valve. By rotating 90 degrees, the channel port on the valve plug is connected or separated from the channel port on the valve body to realize opening or closing.
The shape of its valve plug can be cylindrical or conical. In a cylindrical plug, the channel is generally rectangular; In the conical plug, the channel is trapezoidal. These shapes make the structure of the plug valve lightweight. It is most suitable for cutting and connecting medium and shunting, but sometimes it can also be used for throttling according to the applicable properties and erosion resistance of sealing surface.
Working principle of plug valve
Valve with plug body with through hole as opening and closing part. The plug body rotates with the valve stem to realize the opening and closing action. Small non packing plug valve is also known as “cork”. The plug body of the plug valve is mostly a cone (or a cylinder), which cooperates with the conical hole surface of the valve body to form a sealing pair. Plug valve is one of the earliest valves, with simple structure, rapid opening and closing and low fluid resistance. Ordinary plug valves are sealed by the direct contact between the finished metal plug body and the valve body, so they have poor sealing performance, large opening and closing force and are easy to wear. They can only be used in low pressure (not higher than 1 MPa) and small diameter (less than 100 mm).
Classification of plug valves
According to the structural form, it can be divided into four types: tight plug valve, self sealing plug valve, plug valve and oil filling plug valve. According to the channel form, it can be divided into straight plug valve, three-way plug valve and four-way plug valve. There are also ferrule plug valves.
Plug valves are classified by purpose, including soft seal plug valve, oil lubricated hard seal plug valve, lifting plug valve, three-way and four-way plug valve.
Soft seal soft seal plug valves are often used in harsh environments such as corrosive, highly toxic and high hazard media, where leakage is strictly prohibited, and where valve materials will not pollute the media. The valve body can be made of carbon steel, alloy steel and stainless steel according to the working medium.
Oil lubricated hard seal
Oil lubricated hard seal plug valves can be divided into conventional oil lubricated plug valves and pressure balanced plug valves. Special grease is injected from the top of the plug body between the conical hole of the valve body and the plug body to form an oil film to reduce the opening and closing torque of the valve and improve the sealing performance and service life. The working pressure can reach 64mpa, the maximum working temperature can reach 325 degrees, and the maximum diameter can reach 600mm.
There are many structural forms of lifting plug valve. According to the materials of sealing surface, lifting plug valve is divided into soft seal and hard seal. Its basic principle is to raise the cock when it is opened, and then rotate the cock 90 degrees until the valve is fully open, which can reduce the friction with the sealing surface of the valve body; When closing the valve, turn the cock 90 degrees to the closed position and then lower it to contact the sealing surface of the valve body to achieve sealing.
Tee and cross
The three-way and four-way plug valves are suitable for changing the medium flow direction or medium distribution in Shanghai engineering plant. According to the requirements of service conditions, soft seal bushing or soft seal and hard seal lifting plug valve can be selected.
Advantages of plug valve
1. The plug valve is used for regular operation, and the opening and closing is fast and light.
2. The plug valve has small fluid resistance.
3. The plug valve has the advantages of simple structure, small relative volume, light weight and easy maintenance.
4. Good sealing performance.
5. Not limited by the installation direction, the flow direction of media can be arbitrary.
6. No vibration, low noise.
Installation and maintenance of plug valve
When installing the plug valve, in order to prevent damage to the plug valve and ensure the full performance of the plug valve, pay attention to the following four points:
1. Make sure the valve is open. Heat the pipe first. Transfer as much heat as possible from the pipe to the plug valve. Avoid prolonging the heating time of the plug valve itself.
2. Use gauze or wire brush to remove the pipe and cutting parts to make the metal surface shine. Steel wool is not recommended.
3. First cut the pipe along the vertical direction, trim and remove burrs, and measure the pipe diameter.
4. Apply flux to the outside of the pipe and the inside of the welding cover, and the flux must completely cover the welding surface. Please use flux sparingly.
Selection principle of plug valve
According to the structural characteristics and design functions of the plug valve, it can be selected according to the following principles.
① It is used to distribute medium and change medium flow direction. Its working temperature is not higher than 300 ℃, nominal pressure PN ≤ 1.6Mpa and nominal diameter is not greater than 300mm. It is recommended to select multi-channel plug valve.
② On the equipment and pipelines of food enterprises such as milk, fruit juice and beer and pharmaceutical factories, it is recommended to select tight conical plug valves made of austenitic stainless steel.
③ In the branch pipes, refining and cleaning equipment for oil field exploitation, natural gas field exploitation and pipeline transportation, the nominal pressure level shall not be greater than class300 and the nominal diameter shall not be greater than 300mm. It is recommended to select oil sealed conical plug valve.
④ In the branch pipes, refining and cleaning equipment for oil field production, natural gas production and pipeline transportation, the nominal pressure level is not greater than class7500, the nominal diameter is not greater than 900mm, and the working temperature is not higher than 340 ℃. It is recommended to select oil sealed conical plug valve.
⑤ In the large-scale chemical industry, in the pipeline and equipment containing corrosive medium, where the opening or closing speed is required to be fast, the PTFE sleeve sealed conical plug valve can be selected for the medium based on nitric acid; For the medium based on acetic acid, crl8nil2m02ti stainless steel with PTFE sleeve can be selected to seal the conical plug valve.
⑥ In the pipeline and equipment of gas, natural gas and HVAC system, the nominal diameter shall not be greater than 200nm, and the packing conical plug valve shall be selected.
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