A plug valve is shaped like a cylinder or cone and can be rotated inside the valve body to control flow of fluids. Plug valves have one or more hollow passageways often placed horizontally to allow ease of flow through the valve when open. The most common type of plug valve is the 2 port model with an open and closed position. The two ports are usually located on opposite sides of the valve with one passageway leading from inbound to outbound and the stem and handle located on the top. A plug valve also uses a quarter turn valve, which is useful where quick and frequent operation is essential. The valve ends can be flanged, hub type, or butt weld.
Plug Valve Types and Their Uses
Although there are many types of plug valves, there are four general categories, each with their own benefits.
1. Lubricated Plug Valve
As the name suggests, a lubricated valve uses a lubricant usually made up of a base oil and viscosity improver (like amorphous or fumed silica) that is injected under pressure between the plug face and body seat to reduce friction and seal ports. Valve manufacturers generally recommend lubricant suitable for the process fluid, and the valves often must be resealed after only a few cycles, and in some cases, after every cycle. Considered a high maintenance plug valve, they are often used in applications that have infrequent operations. Lubricated plug valves perform well in processes that utilize fluids which carry mildly abrasive particles such as dirty upstream applications, gas pipeline systems that need bypass valves, and as blow-down valves on valve stations and kicker valves.
2. Non-Lubricated Plug Valve
This plug valve utilizes a tapered or cone-shape that acts as a wedge and presses a polymeric sleeve against the body cavity. The use of the sleeve reduces friction between the plug mechanism and body. Non-lubricated plug valves are often used instead of lubricated ones in applications where maintenance needs to be kept to a minimum, such special services in sulphur, hydrogen fluoride, or where liquids could be trapped or solidify and potentially jam the valve. However, non-lubricated plug valves are limited by temperature and chemical compatibility of the non-metallic materials they are made of.
Plug – heavy-duty fully rubber encapsulated
Welded nickel seat – robotically welded 1/8in thick
Grit-Guard™ shaft seals – prevents bearing wear and shaft seizing
V-type packing – self adjusting and replaceable while under pressure
Stainless steel radial upper and lower bearings – permanently lubricated for extended life
Upper and lower thrust bearings – to assure plug cantering
Packing overload protection Shims – ease of adjustment, extends packing life
Full access cover – allows inline maintenance