Theory of Reciprocating Compressor Operation

The far end of the cylinder is called the head end. The end of the cylinder nearest the central shaft is called the crank end. I have shown the valves only on the head end, to simplify my description of the compressor s operation. 

There are four distinct steps in the compression cycle of the cylinder, shown in Fig. 29.1 compression, discharge, expansion, and intake. 

The initial position of the piston is as far from the cylinder head as possible. This is the start of the compression stroke. This position is called top dead center. The piston now moves toward the cylinder head. The pressure of the gas inside the cylinder increases. 

At some point, as the piston approaches the cylinder head, the gas pressure inside the cylinder exceeds the pressure in Jhe discharge line. The discharge valve now springs open, and gas is pushed out of the cylinder into the discharge line. 

Both the discharge valve and the intake or suction valve are simply spring-loaded check valves. The discharge valve permits gas only to be forced out of the cylinder. The intake valve permits gas only to enter the cylinder. 

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