ENGINEMAN 1 & C
aid in keeping the air supply clean, filters are
fitted to compressor intakes. Unless inspected and
cleaned regularly, these filters become clogged and
cause a loss of capacity.
Filter elements should be removed from the
intake and cleaned either with a jet of hot water
or steam, or by immersion in a strong solution
of sal soda. The filter body should be drained and
replaced. Filter elements of the oil-wetted type
should be dipped in a clean, medium viscosity oil
after cleaning and the excess oil should be
drained from the elements before replacing them
on the filter intakes. Gasoline or kerosene should
not be used for cleaning air filters because of the
explosive fumes which may collect in the com-
pressor or air receiver.
Dehydrators
On some ships, compressed air is used for the
operation of missile system components and with
automatic controls for boilers. In order to pre-
vent failure of these systems, moisture and
lubricants from the compressor must be kept at
a minimum. Blowing down the compressor
separators prevents most of this, but still some
moisture is carried over.
To aid in the removal of the moisture and
lubricants, two types of dehydrators are gener-
ally used: type I refrigerant dehydrators and type
II dehydrators using a desiccant of either silica
gel or activated alumina, and containing electric
heating coils for reactivating the desiccant when
it becomes saturated with moisture. Type II
dehydrators are normally installed in pairs so that
one can always be in service while the other is be-
ing reactivated.
Air Valves
Air inlet and discharge valves are vital parts
of a compressor and should receive careful atten-
tion. When these valves leak, the compressor
capacity is reduced and results in an unbalanced
stage pressure.
There are several symptoms which signify that
an air valve is not functioning properly. A devia-
tion from normal intercooler pressure may
indicate a leaking or broken valve. A defective
inlet valve above the intercooler will cause a rise
in pressure in the intercooler, while a defective
7-2
discharge valve below the intercooler will cause
a decrease in the intercooler pressure. An unusu-
ally hot valve cover is a sign of valve trouble.
Dirt is generally the cause of leaking valves.
The source of valve trouble can usually be traced
to dirty intake air; the use of excessive or improper
cylinder oil; or excessively high air temperature,
resulting from faulty cooling. A periodic inspec-
tion and cleaning of valves and valve passages will
minimize and perhaps prevent the occurrence of
air valve troubles. The frequency for cleaning
valves must be determined for each installation.
The air valves are easily accessible and are
removed by first loosening the valve cover plates.
Then the valve and valve unloader, if installed,
may be lifted out. Each valve should be marked
so that it may later be returned to the same open-
ing from which it was removed.
Dirt or carbon can usually be removed from
valve parts without disassembling the valve. If
disassembly is necessary, notice should be taken
on how the various parts are arranged so that the
proper relationship will be kept when the valve
is reassembled. To remove carbon from valve
parts, soak each part in kerosene and then brush
or scrape lightly. After drying and reassembling
the valve parts, test the valve action to be sure
that the valve opens and closes freely.
Before air valves are replaced in a cylinder,
inspect the gaskets. If the gaskets are made of
materials other than copper, and are damaged,
change them. Copper gaskets should always be
replaced. Since it is often difficult to distinguish
between suction and discharge valves, use extreme
care when inserting valves in the cylinder. Make
sure that suction valves open TOWARD, and
discharge valves AWAY FROM, the center of the
cylinder. Otherwise, serious damage or loss of
capacity will result. If special locknuts are not pro-
vided to seal against leakage at the threads of the
valve setscrew, place a turn of solder or fuse wire
around the screw and set down into a recess by
the locking nut.
Cylinders and Pistons
When you find that it is necessary to inspect
the cylinders or pistons of an air compressor, you
should refer to the manufacturers instruction
manual and the appropriate Planned Maintenance
System (PMS) maintenance requirement card