TM 5-3805-262-343-12. AIR BRAKE SYSTEM MAINTENANCE (CONT)e. AirCompressorAssembly.THEORY OF OPERATION (SHEET 1 OF 2)Lubrication. Oil to lubricate air compressor internal parts is supplied by enginelubricating system. Oil enters rear of air compressor and lubricates crankshaft rearjournal and flows through a passage in the crankshaft to each connecting rod jour-nal. Crankshaft rotary motion then sends this oil to cylinder bores to lubricatepistons and cylinder bores. Wrist pins are lubricated by oil vapors in crankcase andcylinder block.Compression Cycle. During a piston intake (down) stroke, vacuum which is causedabove the piston pulls air into the cylinder through cylinder inlet port and threeholes in cylinder head above inlet valve. At bottom of intake stroke, inlet valvecloses to hold air in cylinder. As piston begins compression (upward) stroke, pres-sure increases in cylinder to hold inlet valve tightly closed. At a specified (andunknown) pressure, exhaust valve is moved off exhaust valve seat so that air incylinder can be sent to air reservoir. At top of compression stroke, exhaust valveis returned to exhaust valve seat to hold air in the line between air compressor andair reservoir.3-464
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