TYPES OF VALVES
Plug valves are available in either a lubricated or nonlubricated design and with a variety of
styles of port openings through the plug as well as a number of plug designs.
An important characteristic of the plug valve is its easy adaptation to multiport construction.
Multiport valves are widely used. Their installation simplifies piping, and they provide a more
convenient operation than multiple gate valves. They also eliminate pipe fittings. The use of
a multiport valve, depending upon the number of ports in the plug valve, eliminates the need of
as many as four conventional shutoff valves.
Plug valves are normally used in non-throttling, on-off operations, particularly where frequent
operation of the valve is necessary. These valves are not normally recommended for throttling
service because, like the gate valve, a high percentage of flow change occurs near shutoff at high
velocity. However, a diamond-shaped port has been developed for throttling service.
Multiport Plug Valves
Multiport valves are particularly advantageous on transfer lines and for diverting services. A
single multiport valve may be installed in lieu of three or four gate valves or other types of
shutoff valve. A disadvantage is that many multiport valve configurations do not completely
shut off flow.
In most cases, one flowpath is always open. These valves are intended to divert the flow of one
line while shutting off flow from the other lines. If complete shutoff of flow is a requirement,
it is necessary that a style of multiport valve be used that permits this, or a secondary valve
should be installed on the main line ahead of the multiport valve to permit complete shutoff of
In some multiport configurations, simultaneous flow to more than one port is also possible. Great
care should be taken in specifying the particular port arrangement required to guarantee that
proper operation will be possible.
Plug Valve Disks
Plugs are either round or cylindrical with a taper. They may have various types of port
openings, each with a varying degree of area relative to the corresponding inside diameter of the
Rectangular Port Plug
The most common port shape is the rectangular port. The rectangular port represents at
least 70% of the corresponding pipe's cross-sectional area.