The second stage of the air cleaner consists of a group of cylindrical pleated paper elements. The ends of the pleats are molded into a flexible plastic faceplate that seals the cartridge in place in the air cleaner housing without additional gaskets. On the side of the air cleaner housing is mounted a service indicator. As the second-stage cartridge loads up with dirt, a red indicator flag gradually rises in the window. When the cartridge is completely loaded, the window shows all red, and the flag is locked in place. This is the time to replace the second-stage cartridge. Discard the old cartridge and reset the red flag, so the window shows clear. Do not clean used paper cartridges.

OPERATION AND MAINTENANCE OF AIR COMPRESSORS

Before the compressor is started, the operator should make inspections to ensure that both the compressor and the auxiliary components are ready for operation. This procedure includes the following: checks of the control and unloading systems; inspection of safety valves or pressure relief valves; draining condensate from the coolers, the separator, and the receiver; and turning on cooling water services and opening valves to ensure proper circulation of water through the compressor and coolers.

Once the compressor is in operation, the operator must periodically check the temperature and pressure of the cooling water, the lube oil, and the compressed air. The lube oil level must also be checked and maintained at the proper level. Coolers must be inspected for correct temperature and flow of water. Accumulations of moisture in the coolers, the separator, and the air receiver must be drained periodically. In addition, maintenance schedules require more detailed inspections (monthly, quarterly, etc.). In many cases, these inspections require dismantling parts of the compressor and auxiliary equipment. For instance, the operator may be required to inspect intake and discharge valves, cylinders, and pistons. The air intake filter must be inspected periodically and cleaned as necessary. The coolers and the receiver must also be inspected for corrosion and accumulations of dirt and oil.

The lubrication system on most compressors is somewhat similar to that on an automobile engine. Normally, the compressor base is used as the lube oil sump and oil pump housing. The oil level can be measured by a dipstick or an oil level sight gauge mounted on the base. The lube oil is distributed through various passages to lubricate bearings, valves, pistons, and other internal parts. An oil film is also distributed over the cylinder walls. Although small amounts of lube oil may mix with the compressed air, it is usually filtered out at the separator assembly. Note that one of the periodic operator inspections on air-lift pumps is to check the air-water discharge from the pump for contamination by lube oil entrained in the compressed air.

The lube oil used in the cylinders must be of the right type. The auto-ignition point (temperature at which oil vapor bums without the presence of a spark or flame) of these oils must always be well above the highest heat of compression; otherwise, there is the danger of internal combustion in the compressor cylinders. An example of a Seabee operated and maintained compressor is discussed in the paragraphs below. The 600 ft3/min, portable air compressor is a single cylinder, sliding vane, oil-cooled, positive displacement rotary compressor, connected through a friction disk clutch to a heavy-duty industrial diesel engine. The complete assembly is equipped with a semi-elliptical spring mounting, pneumatic tires, and drawbar.

The portable compressor comes equipped with all components essential for proper operation, including the following:

A heavy-duty, single, dry-type air cleaner to provide clean air for the compressor and engine with a minimum of service requirements.

Large, cool radiator elements with ample capacity for efficient, dependable cooling of the compressor oil and engine coolant.

Oil filters with replaceable cartridges for efficient filtration of the compressor oil and engine crankcase oil. Automotive-type instrument panel with easy-to- read gauges and electrical instruments.

Pneumatic regulating controls that provide for economical engine operation under all loads.

A combination thermostatic valve and bypass to assure rapid warm-up and optimum compressor performance over a wide range of surrounding air temperatures.

An electrically operated shutdown system to stop the engine if a malfunction occurs in the compressor and/or engine.

A blowdown valve to relieve the pressure in the receiver and air-flow system automatically each time the engine is shut down.