Miscellaneous Mechanical Components
DOE-HDBK-1018/2-93
AIR COMPRESSORS
A section of a typical reciprocating single-stage, single-acting compressor cylinder is shown in
Figure 2. Inlet and discharge valves are located in the clearance space and connected through
ports in the cylinder head to the inlet and discharge connections.
During the suction stroke the compressor piston starts its downward stroke and the air under
Figure 2 Single-Acting Air Compressor Cylinder
pressure in the clearance space rapidly expands until the pressure falls below that on the opposite
side of the inlet valve (Figures 2B and 2C). This difference in pressure causes the inlet valve
to open into the cylinder until the piston reaches the bottom of its stroke (Figure 2C).
During the compression stroke the piston starts upward, compression begins, and at point D has
reached the same pressure as the compressor intake. The spring-loaded inlet valve then closes.
As the piston continues upward, air is compressed until the pressure in the cylinder becomes
great enough to open the discharge valve against the pressure of the valve springs and the
pressure of the discharge line (Figure 2E). From this point, to the end of the stroke (Figures 2E
and 2A), the air compressed within the cylinder is discharged at practically constant pressure.
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