Leakage in compressors is a situation encountered. A leakage occurs when fluid is lost through a leak. All compressors have sliding seals between high and low pressure zones. These always leak to some extent which always has a negative effect on compression efficiency. In reciprocating compressors, the usual leakage paths are through the piston rings, the rod packing of double acting compressors, and the valves, which do not seal perfectly against reverse flow. leakage in compressors
The effects of leakage through the rod packing on double acting compressors and through the piston rings of single acting compressors are easily understood. Some gas that has been at least partially compressed leaks to the atmosphere or a flare line. The power used to compress this gas is wasted and the capacity at discharge is reduced by the amount of the leakage.
Leakage through a suction valve has a double effect. In addition to the loss described for packing leakage, suction valve leakage causes hot gas to enter the suction passage. This is equivalent to heat transfer to the suction gas and has the same negative effect on capacity and efficiency. The change in power is usually small, but may act to reduce the power due to the reduced pressure during the compression process. In most cases, the heating effect causes greater losses than the direct effect.
Discharge valve leakage has the direct effect of wasting gas that has already been compressed, thus decreasing the flow without any decrease in the power. It also increases the pressure in the cylinder during the compression process, thus increasing the power requirement. In addition, the gas that leaks during the expansion and suction processes will heat the gas in the cylinder and reduce the capacity by decreasing the trapped gas density.
Piston ring leakage in a double acting cylinder is a little more complex. Gas leaks into each end of the cylinder during the low pressure part of the cycle and out of the end during the high pressure part of its cycle. In all cases, some of the work that has been done on the gas is wasted as it must be recompressed. In addition, the gas always heats the gas in the end it leaks into. A large amount of the leakage into an end occurs during the suction process. Thus the heating decreases the trapped gas density and decreases the capacity.
