Plug valves, also called cocks,
generally are used for the same full flow service as gate valves, where quick
shut off is required. They are used for steam, water, oil, gas and chemical
liquid service.
Plug valves are not generally
designed for the regulation of flow. Full flow is obtained when the opening in
the tapered plug represent the essential features in plug valves. Careful
design of the internal contours of the valve produces maximum flow efficiency.
The port in the tapered plug is generally rectangular. However, valves are also
available with round ports. Major valve patterns or types are identified as
regular, venturi, short, round port and multi-port.
The regular pattern employs the
tapered form of port openings, the area of which is from 70 to 100 percent of
the internal pipe area. In some cases, the face-to-face lengths are greater
than those of standard gate valves. The venturi pattern provides streamlined
flow and thus permits reduction in the port size. The port opening area is
approximately 35 percent of the internal pipe area. The round-port full-bore
pattern has a circular port through the plug and body equal to or grater than
the inside diameter of the pipe or fitting. Operating efficiency is equal to or
greater than that of gate valves of the same size.
Major types of plug valves
involve lubricated Major types of plug valves involve lubricated and
non-lubricated designs. Lubricant-seal plug valves are less subject to seizing
or wear and may exhibit somewhat greater resistance to corrosion in some
service environments. Non-lubricated plug valves are used where maintenance must
be kept to a minimum. Both types of valves provide a bubble tight closure and
are of compact service applications. Also, plug valves are available with a
wide variety of linings suitable for many chemical service applications.