TYPES OF VALVES
Round Port Plug
Round port plug is a term that describes a valve that has a round opening through the
plug. If the port is the same size or larger than the pipe's inside diameter, it is referred
to as a full port. If the opening is smaller than the pipe's inside diameter, the port is
referred to as a standard round port. Valves having standard round ports are used only
where restriction of flow is unimportant.
Diamond Port Plug
A diamond port plug has a diamond-shaped port through the plug. This design is for
throttling service. All diamond port valves are venturi restricted flow type.
Lubricated Plug Valve Design
Clearances and leakage prevention are the chief considerations in plug valves. Many plug valves
are of all metal construction. In these versions, the narrow gap around the plug can allow
leakage. If the gap is reduced by sinking the taper plug deeper into the body, actuation torque
climbs rapidly and galling can occur. To remedy this condition, a series of grooves around the
body and plug port openings is supplied with grease prior to actuation. Applying grease
lubricates the plug motion and seals the gap between plug and body. Grease injected into a
fitting at the top of the stem travels down through a check valve in the passageway, past the plug
top to the grooves on the plug, and down to a well below the plug. The lubricant must be
compatible with the temperature and nature of the fluid. All manufacturers of lubricated plug
valves have developed a series of lubricants that are compatible with a wide range of media.
Their recommendation should be followed as to which lubricant is best suited for the service.
The most common fluids controlled by plug valves are gases and liquid hydrocarbons. Some
water lines have these valves, provided that lubricant contamination is not a serious danger.
Lubricated plug valves may be as large as 24 inches and have pressure capabilities up to 6000
psig. Steel or iron bodies are available. The plug can be cylindrical or tapered.
There are two basic types of nonlubricated plug valves: lift-type and elastomer sleeve or plug
coated. Lift-type valves provide a means of mechanically lifting the tapered plug slightly to
disengage it from the seating surface to permit easy rotation. The mechanical lifting can be
accomplished with a cam or external lever.