AIR COMPRESSORSDOE-HDBK-1018/2-93Miscellaneous Mechanical ComponentsPressurized air can do the same type of damage as pressurized water. Treat all operations oncompressed air systems with the same care taken on liquid systems. Closed valves should beslowly cracked open and both sides should be allowed to equalize prior to opening the valvefurther. Systems being opened for maintenance should always be depressurized before workbegins. Great care should be taken to keep contaminants from entering air systems. This is especiallytrue for oil. Oil introduced in an air compressor can be compressed to the point wheredetonation takes place in a similar manner as that which occurs in a diesel engine. Thisdetonation can cause equipment damage and personnel injury.SummaryThe important information in this chapter is summarized below.Air Compressors SummaryThe three common types of air compressors are reciprocating, rotary, andcentrifugal.The single-stage reciprocating compressor has a piston that movesdownward during the suction stroke, expanding the air in the cylinder. Theexpanding air causes pressure in the cylinder to drop. When the pressurefalls below the pressure on the other side of the inlet valve, the valveopens and allows air in until the pressure equalizes across the inlet valve.The piston bottoms out and then begins a compression stroke. The upwardmovement of the piston compresses the air in the cylinder, causing thepressure across the inlet valve to equalize and the inlet valve to reseat.The piston continues to compress air during the remainder of the upwardstroke until the cylinder pressure is great enough to open the dischargevalve against the valve spring pressure. Once the discharge valve is open,the air compressed in the cylinder is discharged until the piston completesthe stroke.ME-05Rev. 0Page 8
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