TM 5-3805-262-34
3-12. AIR BRAKE SYSTEM MAINTENANCE (CONT)
e. Air Compressor Assembly.
THEORY OF OPERATION (SHEET 1 OF 2)
Lubrication. Oil to lubricate air compressor internal parts is supplied by engine
lubricating system. Oil enters rear of air compressor and lubricates crankshaft rear
journal 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 lubricate
pistons and cylinder bores. Wrist pins are lubricated by oil vapors in crankcase and
cylinder block.
Compression Cycle. During a piston intake (down) stroke, vacuum which is caused
above the piston pulls air into the cylinder through cylinder inlet port and three
holes in cylinder head above inlet valve. At bottom of intake stroke, inlet valve
closes 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 (and
unknown) pressure, exhaust valve is moved off exhaust valve seat so that air in
cylinder can be sent to air reservoir. At top of compression stroke, exhaust valve
is returned to exhaust valve seat to hold air in the line between air compressor and
air reservoir.
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