Between regular maintenance inspections, be alert
for signs of motor or pump trouble. Common
symptoms are listed in table 6-3. Correct any trouble
immediately and AVOID COSTLY REPAIR AND
What is total discharge head?
The amount of suction lift a pump can provide is
determined by what three factors?
What are the five categories of pumps?
A rotary pump is classified as what type of
What are the types of rotary pumps?
Most reciprocating pumps used in the Navy are
of what four types?
What is the only moving part in a centrifugal
When the velocity of a fluid in a pump
increases, what happens to the pressure
What pumps are used exclusively for well
When an elbow is installed horizontally in
suction piping, what happens to the liquid
entering the pump?
Why should you avoid high spots, such as loops,
in discharge piping?
Widely fluctuating discharge pressure gauge
indicates what type of problem?
On grease-lubricated bearings, what is the
most common problem caused by excessive
What advantage does a mechanical shaft seal
have over packing?
Using table 6-2, how often should you inspect the
packing on a pump?
Using table 6-2, removal and inspection of the
rotating elements of a pump should be
accomplished how often?
LEARNING OBJECTIVE: Recognize types of
air compressor components, accessories,
systems, operation of these systems, and
Air compressors are devices or machines that
compress air. In compression, air at a normal
atmospheric temperature is taken in and sqeezed or
pressed by a moving element within a confined space.
The volume of air is thus reduced, but the pressure, or
force, of the volume of air exerted has increased
considerably. Thus the air develops energy or power
that can be put to some useful purpose in other
machines. The compressed air need not be put to work
immediately but can be stored in tanks to preserve and
maintain its pressure.
Compressed air can be taken from storage bottles
or flasks and used to start diesel engines; that is, the
compressed air is introduced into the diesel cylinders
where, by its pressure, it forces the pistons to
reciprocate until ignition temperature is reached. We
have seen how compressed air forces water to rise in
wells. Air compressors also drive, or power, a wide
variety of pneumatic tools in construction work. The
types of air compressors include reciprocating,
centrifugal, and rotary; however, only reciprocating
compressors are discussed in the following
paragraphs. In basic design and function, these
compressors are similar to the pumps with the same
names. In fact, air compressors are sometimes referred
to as air pumps. Rather than discharging liquid at
relatively high pressure, air compressors discharge air
(which is considered a fluid) at high pressure. Like
pumps, compressors require some external source of
mechanical power to do this work. Prime movers for
air compressors may be electric motors, internal
combustion engines, steam turbines, and so on. The
majority of air compressors used throughout the Navy
are driven by electric motors.
RECIPROCATING AIR COMPRESSORS
One of the most commonly used air compressors in
the naval service is the reciprocating air compressor. It
compresses air in the same manner as a diesel engine.
A reciprocating piston alternately draws in and then
compresses the trapped air in a cylinder. Since there is
no internal combustion, the cycle of the reciprocating
air compressor is reduced or simplified to two strokes-
suction (intake) and compression. Instead of operating
the valves by cam action, as in internal combustion
engines, the intake and discharge valves of the
reciprocating air compressor operate on the principle
of differential pressure overcoming spring tension,