A decrease in the efficiency of a reciprocating compressor is most likely caused by which of the following?

• A. Leaking suction valve
• B. Stuck discharge valve
• C. Over-lubricated bearings
• D. Low ambient temperature

Answer: (A)

Volumetric efficiency and valve sealing in a reciprocating compressor are what this item tests. If the suction valve leaks, some of the gas just drawn into the cylinder can slip back through the valve during the compression stroke. That means less gas is actually compressed and delivered per cycle, so the net output falls while the motor still has to work to re-compress the leaked gas. The result is lower efficiency and higher energy use for the same output. A stuck discharge valve would primarily block discharge and create flow and pressure problems, over-lubricated bearings add friction but aren’t the typical driver of this efficiency drop, and low ambient temperature doesn’t usually cause a decrease in efficiency in the same way suction leakage does.