Plug valve has a conical or cylindrical shaped plug which rotates inside the body of the valve to control the flow of the liquid. The horizontal passage present in the plug enables the flow when the valve is opened while the. Quarter-turn rotation of the valve opens or closes it. When turned by 90 degrees from the open position, the solid part of the plug terminates the flow.
Parts of a plug valve
Apart from the plug, a plug valve has a body, bonnet and stem. The body of the valve is connected to the plug.
Types of plug valves
Lubricated plug valves- The plug in a lubricated plug valve has a cavity in the middle portion along the axis. Lubricant is injected into the cavity. The sealant injection fitting at the top and the check valve below the injection fitting ensure that the lubricant does not flow in the reverse direction. There is also a lubricant chamber at the bottom to ensure constant supply of lubricant. The lubricant present in the central cavity of the plug reaches the lubricant grooves on the surface of the plug through radial holes. The lubricant decreases the force generated during opening and closing of the plug valve and also protects the plug against corrosion. The lubricant also prevents internal leakage by forming a seal between the body and the plug. The lubricant must be compatible with the liquid flowing through the valve and it must also not be washed away by the liquid. The temperature of the liquid must also not have any effect on the lubricant. Lubricated plug valves are used to control the flow of acids, alkalis, oils, steam, gases and many other media.
Non-lubricated plug valves- Non-lubricated plug valve has a non-metallic sleeve or liner in the cavity of the plug. The non-metallic serves to decrease the friction between the plug and body of the valve. This kind of valve cannot be used for high temperature operations because of the non-metallic sleeve. The chemical compatibility of the non-metallic element must also be kept in mind before installing this valve.
Applications of plug valves
Plug valves are commonly used for processes which require frequent adjustment of the flow rate. The valve enables you to quickly increase or decrease the flow rate. Plug valves are used in natural gas pipes as well as oil pipes. They are also used for air and gas, coal slurries, sewage, acidic liquids and high pressure systems.
