The plug valve has the shape of a hollow cylinder valve to regulate flow. When the axis of the cavity is parallel to the axis of fluid flow, the valve is fully open. If the axis of the cavity is perpendicular to the axis of flow, the valve is tightly closed.
The tapered plug provides quarter-turn operation from fully open to fully closed. When in the open position, and completely blocking flow when rotated 90° to the closed position.
Plug valves are used for a condition where a quick ON / OFF and/or bubble tight closure is required. Most plug valve styles are available in the full range of pipe sizes and materials that are needed in process plant applications.
Types of Plug valve:
There are three basic plug valve-types: the lubricated, nonlubricated, and soft-sealed fire safe.
Lubricated Plug Valve:
A lubricant is injected in between the plug face and body seat to reduce friction and seal ports. The lubricants are selected based on the process fluid used. The sealant is injected through a pressure fitting into the body cavity and distributed across all seating surfaces via grooves in the plug.
Lubricating valves can provide longer life if proper maintenance attention can be guaranteed. With its substantial metal-to-metal secondary seat and the ability to re-establish the seal by injecting sealant, this type of valve inherently shoots reliably with respect to through-filtration.
Non - Lubricated plug valve:
Non-Lubricant valves are used where less maintenance is required. The friction between the plug cone and body is reduced by sleeves. However, non-lubricated plug valves are limited by temperature and chemical compatibility of the non-metallic materials.
Non-lubricating valves are used to regulate the process fluid, such as sulfur, hydrogen fluoride, or where liquids could be trapped or solidified and potentially clog the valve.
Soft-Sealed, Fire-safe Plug Valve:
Fire safety plug valves use a narrow-band primary sealing ring made of a flexible, elastic material (such as Teflon) in the ring between the plug and the body cavity to prevent leakage.
A fire safe soft seal valve also has a secondary metal-to-metal backup seal. This ensures a positive closing capability if the soft seal is damaged by fire. The maximum temperature limit of the valve is limited by the soft-seal material.
Gas and liquid fuel control
At boiler feed water
Low preassure steam.
For extreme temperature flow.