2. A dew point temperature reading of -40°F or
lower at 80 lb/in2 is normal for LP (type II and type III)
dehydrators. A reading of -20°F or higher at 80 lb/in
indicates that the dehydrator is not operating properly,
and you should check the applicable technical manual
to correct the problem.
3. For HP air dehydrators, a dew point temperature
reading of -60°F or lower at atmospheric pressure is
normal. A reading higher than -60°F at atmospheric
pressure indicates that the dehydrator is not working
properly, and you should check the technical manual for
the solution to the problem.
MAINTENANCE OF RECIPROCATING
To keep the ships air compressors operating
efficiently at all times, you must know what common
troubles may occur and their causes. You must know
how to care for the air intakes; how to maintain and
replace air valves; how to take care of air cylinders and
pistons; and how to adjust bearings, wrist pins, and
couplings. You must be able to maintain, troubleshoot,
and repair the lubrication, cooling, control, and air
A supply of clean, cool, dry air is essential to the
satisfactory operation of compressors. To ensure this,
the air intake filters must be regularly inspected and
cleaned; otherwise, the filter becomes clogged and
causes loss of capacity. A clogged air intake screen or
filter may also cause a compressor to draw oil from its
own crankcase, around rings, or through oil seals,
resulting in an explosion.
Remove the filter element and clean it with a jet of
hot water or steam, or plunge it into a strong solution of
sal soda. The filter body should be drained and replaced.
If the filter is the oil-wetted type, dip it in clean,
medium-grade oil and allow it to drain thoroughly
before replacing the filter in the intake. Do not use
gasoline or kerosene for cleaning filters! The fumes
may collect and explode in the compressor or receiver.
Take care to prevent entrance of rain or spray into
intake pipes, and provide a means for draining the intake
pipe of any water that may collect. The lines should be
as short and direct as possible.
For air compressors used to supply air for the divers,
you must prevent the compressor from taking in exhaust
gases coming from any internal combustion engines.
You must also prevent any possible intake of fumes
coming from fuel tank vents, spilled oil, or gasoline.
Air inlet and discharge valves must be kept clean
and in good working order. Leaky valves are generally
dirty valves, and they cause capacity loss. The valves
are removed by first loosening their setscrews or
clamps, and then removing their cover plates. Each
valve and valve unloader, if fitted, may then be lifted
out. Each valve should be marked to make certain that
it is returned to the same port from which it was
Valves removed for inspection should not be taken
apart for cleaning unless their conditions make it
necessary. Dirt or carbon in valve ports can usually be
removed without taking the valve apart. This is done by
soaking the valves in kerosene, and then giving them a
stiff brushing or a light scraping. Valve action should be
tested by inserting a screwdriver through the seat ports;
the valve should lift and close freely.
If it becomes necessary to disassemble the valve,
note the arrangement of the various parts so that the
proper relationship will be kept when the valve is
reassembled. (Periodic shipboard reports indicate
damage to pistons and associated valve parts frequently
results from improperly assembled valves that protrude
in the way of the oncoming piston.)
Before replacing air valves in a cylinder, inspect the
gaskets and replace any that are damaged.
Copper-covered asbestos or plain, thin copper gaskets
should be used. If these are not available, 1/16-inch
compressed-asbestos sheet gaskets may be used
temporarily. Each valve assembly should be inserted in
the same hole from which it was removed. Since it may
be difficult, in many cases, to distinguish between
suction or discharge valves, extreme care must be taken
when the valves are being inserted in the cylinder. Make
certain that suction valves open TOWARD, and the
discharge valves AWAY FROM, the center of the
cylinder; otherwise, serious damage or loss of capacity
will result. Then place the valve cover on the cylinder,
making certain that its gasket is squarely in place; draw
down on the cover nuts evenly, and in turn, so as not to
tilt the cover. Tighten down the valve setscrew or
clamping bolt, drawing it tight to hold the valve on its
seat. If special locknuts are not provided to seal against
leakage at the threads of the valve setscrew, a turn of
solder or fuse wire should be placed around the screw
and set down into a recess by a locking nut.