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. Corken’s 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 compressor chamber to prevent contamination of the gas.
Depending on the type of gas, there will be one to three sets of packing per piston rod. One set of packing controls leakage and oil contamination of the vapor to a satisfactory level for most commercial LP gas and ammonia applications. When leakage and contamination must be held to an absolute minimum, three sets of packing separated by two distance pieces may be utilized. Corken manufactures vertical and horizontal compressors with single, double and triple packing options.
The crankcase converts rotary motion from the motor to reciprocating motion at the piston. With the exception of the model 91, all of Corken’s compressors have an oil pump that pressure lubricates the bearings and wrist pins. The oil pump is a gear type that may be run in either direction. As a result, the Corken compressor may be turned in either direction.
For more information on Corken’s reciprocating gas compressors, click on one of the links below.