In order for ships air compressors to work effectively, at any time,
you should know what the most common problems can occur and their
causes. You need to know how to take care of vents; How to hold and
replace the air valves; Maintenance of pneumatic cylinders and pistons;
And like the bearings adjust, crank pins and links. You should be able
to replace and repair the lubrication , cooling, control and air
systems.
AIR INTAKES
A clean, dry air
is essential to the proper operation of the compressors. To do this, the
air intake filters should be regularly inspected and cleaned; If the
filter is clogged there is a loss of capacity. A clogged air screen or
inlet filter can also lead to extraction of oil from a compressor
crankcase, around the rings or through oil seals to cause an explosion.
Remove the filter element and clean with a jet of hot water or steam or
by immersing in a strong solution of sodium hydroxide. The filter
housing must be drained and replaced. When the filters are soaked in
oil, dipping in clean oil, intermediate and complete emptying must be
done before the filter at the inlet changes. Do not clean the filter
with petrol or kerosene! Vapors can accumulate and explode in the
compressor or the receiver. Make sure that no rain or dew on the inlet
side be present and a means to drain the water from suction tube be
provided. The lines should be as short and direct as possible. To supply
air compressor air to the divers, avoiding compressor absorbs every
internal combustion engine exhaust. You should also avoid possible
inlets fumes from the fuel tank, spilled oil or gasoline.
AIR VALVES
The
inlet and exhaust must be clean and kept in good condition. The valves
if have leakage are generally contaminated and cause a loss in capacity.
Valves are removed by loosening the fastening screws or clamps and then
removing the cover plates. Each relief valve , if provided, can be
lifted. Each valve should be checked to ensure that it returns to the
same port from which it was removed. The valves removed for inspection
should not be removed for cleaning if the conditions so require.
Usually, dirt or carbon in the valve hole can be removed without
removing the valve. This is done by soaking the valves in kerosene, then
giving a stiff, light brushing or light scraping. The action of the
valve is to be tested by inserting a screwdriver through the seat
opening; The valve must lift and close freely. If necessary, remove the
valve, check the arrangement of the various parts so that the
corresponding relationship is maintained with the valve assembly. (The
periodic reports on board show damage to the piston and valve parts if
connected poorly mounted valves in the way of the piston lugs protrude.)
Before replacing the cylinder in a cylinder, replace the air valves,
check the seals and replace them. Plates coated with copper or asbestos
thin and thin copper. Alternatively, they can be used together of
compressed asbestos temporary 1/16 inch. Each valve assembly is inserted
into the same hole that has been removed. Since it may be difficult in
many cases to distinguish between the suction valve and the pressure
valve, care must be taken when the valves are inserted into the
cylinder. Make sure the suction valves are open to the center of the
cylinder and exhaust valves are clear. Failure to do so will result in
serious injury or loss of capacity. Then, the valve cap in the cylinder
ensures that the gasket is in place; Lower even coverage of nuts and
again do not tilt the lid. Tighten the set screw of the valve or
clamping screw, pulling the valve in its seat. If no special lock in the
threads of the screw of the valve to prevent leakage leakage must be
placed through a locking nut in a recess around the screw and placing
welding or fuse wire.
CYLINDERS AND PISTONS
The
cylinders on pistons should be inspected only AFTER the
manufacturer’s technical manual has been consulted. Be careful
when removing heads, particularly where metal-to-metal joints
are involved, to prevent damage to the joint.
If replacement of
piston rings is required because they are worn or broken, take accurate
measurements of the cylinder liners. Standard size rings may be used in
oversize cylinders if the oversize does not exceed 0.003inch per inch of
cylinder diameter. The liner may also need to be replaced if it is
badly worn or out of round. When replacing piston rings, first fit them
to the cylinder to check for proper end clearance. You can file the
ends, if necessary, to make them fit. The side clearance of the rings
should be such that the rings will fall easily into the piston grooves,
which should be deep enough for the ring thickness. Ring splits should
be staggered. After you assemble the piston, wire the rings tight with a
soft copper wire so that they will enter the bore easily. This wire can
be removed through the valve ports after the ring has started into the
cylinder bore.
When reassembling the air cylinders and heads, be
sure they are all drawn down evenly, especially on multistage
compressors where the heads contain cylinders for third and
fourth stages. Otherwise, the result will be excess wear on the
cylinders and pistons.
When a compressor piston has been
replaced, the piston end clearance must be checked. This is done by
inserting a lead wire through a valve port or indicator connection. Jack
the compressor over. When the piston has moved to the end of its
stroke, the lead will be flattened to the exact amount of
clearance. The wire should be long enough to permit a reading
near the center of the piston. These readings should be taken after
any adjustment or replacement of the main, crank pin, wrist pin, or
crosshead bearings. Methods of adjusting the clearances vary according
to the compressor design. You should consult the manufacturer’s
instructions for suggested adjustment.
MISCELLANEOUS ADJUSTMENTS
From time to time other miscellaneous adjustments are
required on compressors, including those pertaining to wrist
pins, crosshead shoes, reduction gears, couplings, and V-belt
drives. The manufacturer’s technical manual will give you specific
information forth care, adjustment, and replacement of all
fitted bearings. Refer to the manufacturer’s instructions for
detailed information on when and how to make these adjustments.
Wrist
pin bushings are replaced when necessary. This is done when they
are worn to the point of becoming noisy. In making a replacement,
be sure the oil hole in the bushing is properly lined up with the oil
hole in the connecting rod. After being pressed into the rod, the new
bushing must be reamed.
Crosshead shoes are provided with shim or
wedge adjustment. Wear should be slight, but adjustment
should be made when the travel of the piston rod causes movement in the
stuffing boxes.
Alignment of reduction gears and pinions should be
checked periodically, especially on a new compressor. Misalignment may
be caused later by settling, straining, or springing of
foundations; pipe strains on turbine-driven compressors; bearing
wear; or springing due to heat from a turbine.
Flexible couplings
require very little maintenance when they are properly lined up. Some
types require occasional lubrication to prevent excessive wear of
springs and bushings. A noisy coupling is an indication that the bushing
is worn and requires replacement.
V-belt drives require
adjustment for belt tension. Belts generally stretch slightly during the
first few months of use. A loose belt will slip on the motor pulley and
cause undue heating and wear on the belt. A tight belt will overload
the bearings. Belts should be protected against oil and high
temperatures. To prevent rapid deterioration, belts should not be used
at temperatures above 130°F. V-belts are usually installed in sets of
two or three. If a single belt is worn or deteriorated, the complete
set should be replaced to ensure that each belt will carry its share of
the load.
LUBRICATION SYSTEM
Proper care of a compressor lubrication system includes the following:-
- Keep the oil at a normal level in the reservoir at all times to maintain proper oil temperature.
- Change crankcase oil periodically, and at the same time clean and flush the crankcase and clean the oil filter.
- Maintain proper lube-oil pressure by keeping the oil pump in good working order and adjusting the bypass relief valve.
- Keep the oil cooler free from leaks (since pressure on the water side exceeds that of the oil) to prevent oil contamination and emulsification.
- Properly adjust the lubricator for the specified quantity of oil feed.
COOLING SYSTEM
Proper care of a compressor cooling system includes the following inspections and maintenance procedures:
- Periodically inspect the intercoolers and aftercoolers
- Remove collections of gummy oils or tarry substances from the cooler tubes by washing tube nests with a suitable solvent and drying them thoroughly before reassembling.
- Correct any leakage in tube nests to prevent leaks of water into the compressor while secured or leaks of air into the water side during operation.
- Inspect and clean the cylinder water jackets periodically with a cleaning nozzle.
When
filling the cooling water system after the compressor has been
drained, open the water inlet slightly to allow the water to rise
slowly in the cooler shells and water jackets. Vent valves fitted to the
water spaces should be opened to permit entrapped air to escape and to
remove any air pockets.
CONTROL DEVICES
Because
of the great variety of regulating and unloading devices used on
compressors, you will have to consult the manufacturer’s
technical manual for information regarding the adjustment of these
device son particular compressors.
If a control valve fails to
work properly, it should be taken apart and cleaned Some valves are
fitted with filter filled with a sponge or woolen yarn to
prevent particles of dust or grit from being carried into the valve
chamber. These filters remove gummy deposits from the oil used in the
compressor cylinders. When repacking, use only genuine wool. Cotton will
pack and stop the airflow. Relief valves are very important
for safe compressor operation. They should be set as specified by
the manufacturer and lift-tested by hand each time the compressor is
placed in operation. To check the setting periodically, test by raising
the pressure in the spaces to which they are attached.
SUMMARY
Since
an Engine man may encounter so many types of compressed air
systems, air dryers, and air compressors both ashore and
aboard Navy vessels, this chapter presented only general procedures and
facts. To maintain, repair, and overhaul specific compressed air
systems, air dryers, or reciprocating air compressors, you must
refer to the manufacturer’s technical manuals. A definite
preventive maintenance schedule with frequency and assignment of
responsibility is required. You should have the manufacturer’s manual
handy to establish minimum requirements and to follow its
recommendations for maintenance.
Author Amit Article Requested By: Rauhjek
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