Reciprocating compressor

When a reciprocating compressor compresses gas, the gas is compressed by the piston, thereby increasing the gas pressure. Typically, the compressed high-pressure gas is sent to the next stage of the system, such as a gas storage tank or an industrial process. When we say that the return flow of a reciprocating compressor is fully open, it means that the compressor’s exhaust valve or some other mechanism for allowing return flow is opened, enabling the compressed gas to flow directly back to the suction side. In this case, the compressor does compress the gas, but since the gas is not actually delivered to other parts of the system and instead returns directly to the suction side, the compressor does not actually provide useful work to the entire system. At this point, although the pressure rises temporarily during compression, the gas immediately returns to the inlet side; as a result, the gas circulates within the compressor and fails to push the gas in the system forward. Since no gas flows into the system, the pressure within it does not actually increase, even if the pressure inside the compressor rises momentarily. In short, even though the compressor compresses the gas, since the gas is not sent out of the compressor to perform further work or be stored, the compressor essentially does no work externally. In this case, the energy consumed by the compressor is actually converted into the internal energy of the gas, and may be dissipated as heat; meanwhile, the pressure and volume conditions of the gas return to their initial values, so the inlet pressure remains unchanged. .

1. The compressor is doing work； 2. The inlet pressure does not rise because of the pressure reducing valve.

With the check valve fully open, there is only one check valve on the return line; there are no shut-off elements anymore

“Why is it said that the compressor does no work when the return flow of the reciprocating compressor is fully open? ”Once the gas enters the compressor cylinder, isn’t it already compressed? So the outlet pressure should have increased by now.” “Then it returns to the inlet – why doesn’t the inlet pressure increase at that point? “. There are three questions in total, but all of these questions were formulated by you yourself. Firstly, question 1 refers to the fact that the outlet pressure at the total compressor outlet has not increased, meaning no work is being done. Question 2: Due to the characteristics of piston compressors, the compressed gas is promptly drawn in. Question 3: This is because the operating process of the entire compressor at this time involves cycling through equal amounts of work. It is not accurate to simply say that no work is done; if a fluid closed loop lacks cooling facilities, it will cause the temperature of the system to rise. This increase in temperature is also a form of work; the heating caused by friction due to fluid flow is all considered work as well. It is not accurate to measure whether work is being done solely based on an increase in pressure. For reference.