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Reciprocating Gas Compressors Explained

Reciprocating compressors pull vapor into a cylinder through a suction valve by drawing back a piston to create a low pressure area in the cylinder. They pressurize the gas by pushing the piston back up into the cylinder to squeeze the gas out through the discharge valve.

A compressor valve consists of four parts: a seat, bumper, disc and spring. The spring rests against a bumper and pushes the disc against the seat. The disc seals off the flow passage through the seat. If more pressure builds up on the seat side than the bumper side, the disc will be forced away from the seat and gas will flow through the valve.

In order for compression to take place, the piston must be sealed against the wall. This seal is made with several piston rings. To avoid contaminating the process gas with lubricating oils, the piston rings must be made of a self- lubricating material. Compression piston rings are usually made of glass-filled PTFE. Gas pressure in the cylinder is used to press the piston ring against the cylinder wall. Ring expanders are used to push the ring towards the cylinder wall so high pressure gas may flow behind the ring.

Piston rings form a good dynamic seal but they are not tight enough to seal all the pressure and gas inside the cylinder; and additional seal is required to do this. This seal is the piston rod packing. The piston rod and packing is a seal that is located at the bottom of the cylinder. It is composed of several parts, the most important being the self-lubricating PTFE V-rings that slightly seal against the piston rod. A spring is included in the packing assembly which allows a slight amount of float to reduce the friction. The rod packing also seals oil in the crankcase out of the compress