With positive displacement compressors variations in gas composition (molecular weight, specific heat ratio, compressibility), gas pressure and gas temperature are less critical than they are in dynamic compressors. While small changes have a minimal effect on compressor operation, large changes could exceed the available driver power, fail to meet the required throughput or fail to achieve the required discharge pressure. In such a case the compressor could continue to operate at
reduced throughput and power. However, failure to achieve the required discharge pressure would shutdown the operation.
Reciprocating compressors are designed to operate across a range of pressures or system resistances. the characteristic curve between the high and low system resistance lines is almost a straight vertical line. At very high differential pressures flow starts to decrease. Operation in this range usually results in failure (seals, piston rods, bearings).
One of the major causes of failure in reciprocating compressors is liquids or hydrates in the gas. Only very small amounts of liquid can be expelled through the discharge valve. However, prolonged operation even with a small amount of liquid will lead to valve failure. If the volume of the liquid exceeds the clearance volume either the rod will bend
or the piston will fail. Therefore, it is imperative that the gas entering
the compressor is dry and free from liquids or hydrates.