as thermostatic recirculating valves. The follow-
restriction is desired. Gate valves are so named
because the part which either stops or allows flow
ing sections deal first with the basic types of stop
valves and check valves, then with some of the
through the valve acts somewhat like the opening
more complicated special valves.
or closing of a gate and is called, appropriately,
the gate. The gate is usually wedge shaped. When
the valve is wide open, the gate is fully drawn up
Stop Valves
into the valve, leaving an opening for flow
through the valve the same size as the pipe in
Stop valves are used to shut off or, in some
which the valve is installed. Therefore, there is
cases, partially shut off the flow of fluid. Stop
little pressure drop or flow restriction through the
valves are controlled by the movement of the valve
valve. Gate valves are not suitable for throttling
stem. Stop valves can be divided into four general
purposes since the control of flow would be
categories: globe, gate, butterfly, and ball valves.
difficult due to valve design and since the flow
Plug valves and needle valves may also be
of fluid slapping against a partially open gate can
considered stop valves. Since plug valves and
cause extensive damage to the valve. Except as
needle valves are covered sufficiently in Fireman,
specifically authorized, gate valves should not be
NAVEDTRA 10520, we will not discuss them in
used for throttling.
this manual.
Gate valves are classified as either RISING-
GLOBE VALVES.--Globe valves are prob-
STEM or NONRISING-STEM valves. On the
ably the most common valves in existence. The
nonrising-stem gate valve shown in figure 6-2, the
globe valve derives its name from the globular
stem is threaded on the lower end into the gate.
shape of the valve body. However, positive
As the handwheel on the stem is rotated, the gate
identification of a globe valve must be made
travels up or down the stem on the threads, while
internally because other valve types may have
the stem remains vertically stationary. This type
globular appearing bodies. Globe valve inlet and
of valve almost always has a pointer-type indicator
outlet openings are arranged in several ways to
threaded onto the upper end of the stem to
suit varying requirements of flow. Figure 6-l
indicate valve position.
shows the common types of globe valve bodies;
straight-flow, angle-flow, and cross-flow. Globe
valves arc used extensively throughout the
engineering plant and other parts of the ship in
a variety of systems.
GATE VALVES.--Gate valves are used when
a straight-line flow of fluid and minimum
Figure 6-2.--Cutaway view of a gate valve (nonrising-stem
Figure 6-1.--Types of globe valve bodies.
type).
6-2
