NAVEDTRA 12001, there are two main groups of
valves: stop valves and check valves. Stop valves are
Every piping system must have some means to
used to shut off (or, in some cases, to partially shut off)
control the amount and direction of the flow of liquids
the flow of fluid. These valves are controlled entirely
or gas through the lines. This is accomplished by
by the movement of the valve stem. Check valves are
installing valves, which can be opened or closed as
used to permit the flow of fluid in one direction only.
These valves are controlled by the movement of the
Valves are usually made of bronze, brass, cast or
malleable iron, or steel. Steel valves are either cast or
Valve designs vary considerably because of the
forged, and are made of carbon steel, low ahoy steel, or
different demands of services. Some valves are
stainless steel. Alloy steel valves are used in
high-pressure, high-temperature systems. The disks and
mentioned. Special valves, such as reducing valves,
seats of these valves are usually surfaced with a
bear only a slight resemblance to the basic types.
chromium-cobalt alloy known as stellite. This material
However, stop valves may include globe valves, gate
is extremely hard.
valves, piston valves, plug valves, needle valves, and
Bronze and brass valves are not used in
butterfly valves. Check valves may include
high-temperature systems, or in any system in which
swing-check valves and lift-check valves.
they would be exposed to severe pressure, vibration, or
shock. Bronze valves are widely used in saltwater
systems. The seats and disks of bronze valves used for
saltwater service are often made of Monel, which is
stop valves. They get their name from the globular
highly resistant to corrosion and erosion.
shape of their bodies. However, other types of valves
Many different types of valves are used to control
may also have globe-shaped bodies, so do not jump to
the flow of liquids and gases. As described in Fireman,
the conclusion that a valve with a globe-shaped body is