MAINTENANCE OF RECIPROCATING AIR COMPRESSORS
MAINTENANCE OF RECIPROCATING AIR COMPRESSORS
To keep the ship’s 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 systems
AIR INTAKES
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 VALVES
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 removed.
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.
