Miscellaneous Mechanical Components
Pressurized air can do the same type of damage as pressurized water. Treat all operations on
compressed air systems with the same care taken on liquid systems. Closed valves should be
slowly cracked open and both sides should be allowed to equalize prior to opening the valve
further. Systems being opened for maintenance should always be depressurized before work
Great care should be taken to keep contaminants from entering air systems. This is especially
true for oil. Oil introduced in an air compressor can be compressed to the point where
detonation takes place in a similar manner as that which occurs in a diesel engine. This
detonation can cause equipment damage and personnel injury.
The important information in this chapter is summarized below.
Air Compressors Summary
The three common types of air compressors are reciprocating, rotary, and
The single-stage reciprocating compressor has a piston that moves
downward during the suction stroke, expanding the air in the cylinder. The
expanding air causes pressure in the cylinder to drop. When the pressure
falls below the pressure on the other side of the inlet valve, the valve
opens and allows air in until the pressure equalizes across the inlet valve.
The piston bottoms out and then begins a compression stroke. The upward
movement of the piston compresses the air in the cylinder, causing the
pressure across the inlet valve to equalize and the inlet valve to reseat.
The piston continues to compress air during the remainder of the upward
stroke until the cylinder pressure is great enough to open the discharge
valve against the valve spring pressure. Once the discharge valve is open,
the air compressed in the cylinder is discharged until the piston completes