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Plug valves
are valves with cylindrical or conically-tapered "plugs" which
can be rotated inside the valve body to control flow through the
valve. the plugs in plug valves have one or more hollow
passageways going sideways through the plug. Plug valves are
simple and often economical.
When the plug is conically-tapered, the stem/handle is typically
attached to the larger diameter end of the plug. Plug valve
usually do not have bonnets but often have the end of the plug
with the handle exposed or mostly exposed to the outside. The
stem and handle often come in one piece, often a simple,
approximately L-shaped handle attached to the end of the plug.
The other end of the plug is often exposed to the outside of the
valve too, but with a mechanism which retains the plug in the
body.
The simplest and most common general type of plug valve is a
2-port valve, which has two positions, open to allow flows, and
shut (closed) to stop flow. Ports are openings in the valve body
through which fluid can enter or leave. The plug in this kind of
valve has one passageway going through it. The ports are
typically at opposite ends of the body; therefore, the plug is
rotated a fourth of a full turn to change from open to
shut positions. This makes this kind of plug valve a quarter
turn valve. There is often a mechanism limiting motion of the
handle to a quarter turn, but not in glass stopcocks.
Slightly conically-tapered metal (often brass) plug valves
are often used as simple shut-off valves in household natural
gas lines.
It is also possible for a plug valve to have more than two
ports. In a 3-way plug valve, flow from one port could be
directed to either the second or third port. A 3-way plug valve
could also be designed to shift flow between ports 1 and2, 2 and
3, or 1 and3, and possibly even connect all three ports
together. |
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