governor maintains a constant discharge pressure,
regardless of pump capacity or output. Most
constant-pressure pump governors used in the
Navy control steam-driven pumps, both rotary
and centrifugal types.
The constant-pressure pump governor (some-
times referred to as pressure-regulating) consists
essentially of an automatic throttling valve
installed in the steam supply line to the pump’s
driving unit. A pipeline connects the governor to
the pump’s discharge line. Variations in discharge
pressure, or in pressure differential, actuate
the governor, causing it to regulate the pump
speed by varying the flow of steam to the driving
unit.
A constant-pressure pump governor for a
lubricating oil service pump is shown in figure
9-17. The governors used on fuel oil service
pumps and on main feed pumps are of the same
type. The size of the upper diaphragm and the
amount of spring tension vary on governors
used for different services. You will find
detailed information concerning the operation and
adjustment of governors in chapter 503 of the
NSTM.
VALVES
A valve is any device used to control fluids
in a closed system. In this section we will discuss
valve construction and the most common types
of valves you will use in the day-to-day operation
and maintenance of the various shipboard
engineering systems. Valves are typed or classified
according to their use in a system.
VALVE CONSTRUCTION
Valves are usually made of bronze, brass,
cast or malleable iron, or steel. Steel valves
are either cast or forged and are made of either
plain steel or alloy steel. Alloy steel valves are
used in high-pressure, high-temperature systems;
the disks and seats (internal sealing surfaces) of
these valves are usually surfaced with a chromium-
cobalt alloy known as Stellite. Stellite is extremely
hard.
Brass and bronze valves are never used in
systems where temperatures exceed 550°F. Steel
valves are used for all services above 550°F and
in lower temperature systems where internal or
external conditions of high pressure, vibration,
or shock would be too severe for valves made
of brass or bronze. Bronze valves are used
almost exclusively in systems that carry salt
water. The seats and disks of these valves
are usually made of Monel, a metal that
has excellent corrosion- and erosion-resistant
qualities.
Most submarine seawater valves are made of
an alloy of 70 percent copper to 30 percent nickel
(70/30).
VALVE TYPES
Although many different types of valves are
used to control the flow of fluids, the basic valve
types can be divided into two general groups: stop
valves and check valves.
Besides the basic types of valves, many
special valves, which cannot really be classified
as either stop valves or check valves, are
found in the engineering spaces. Many of these
valves serve to control the pressure of fluids
and are known as pressure-control valves. Other
valves are identified by names that indicate
their general function, such as thermostatic
recirculating valves.
The following sections
deal first with the basic types of stop valves
and check valves, then with some of the more
complicated special valves.
Stop Valves
Stop valves are used to shut off or, in
some cases, partially shut off the flow of fluid.
Stop valves are controlled by the movement of
the valve stem. Stop valves can be divided into
four general categories: globe, gate, butterfly, and
ball valves. Plug valves and needle valves may also
be considered stop valves.
GLOBE VALVES.— Globe valves are probably
the most common valves in existence. The globe
valve derives its name from the globular shape of
the valve body. However, positive identification
of a globe valve must be made internally because
other valve types may have globular appearing
bodies. Globe valve inlet and outlet openings
are arranged in several ways to suit varying
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