The suction service valve of a reciprocating compressor is front seated and the machine runs until the low pressure cut-out shuts the compressor off. When the machine is stopped, suction pressure tends to rise rapidly. What is the most probable cause?

• A. Malfunction of a compressor valve
• B. Overheating
• C. Wrong lubricant
• D. Pipe blockage

Answer: (A)

When a reciprocating compressor stops and suction pressure suddenly climbs, it points to backflow from the high-pressure discharge side into the suction side once the moving parts are no longer guiding gas with each stroke. The suction gas should not be pushed back into the suction line if all valves seal properly. If a compressor valve isn’t sealing correctly, gas can leak past from the discharge side into the cylinder and then into the suction line whenever the unit stops, causing a rapid rise in suction pressure. This is exactly what you’d expect from a valve that isn’t operating correctly.

The other possibilities don’t fit this symptom. Overheating affects temperatures and possibly pressures differently and wouldn’t typically cause a rapid suction-pressure spike upon shutdown. Using the wrong lubricant tends to cause wear or lubrication issues rather than a sudden backflow pressure rise. A pipe blockage would more likely restrict flow and lower suction pressure rather than cause a quick increase after shutdown.

So, the rapid rise in suction pressure after stopping best indicates a valve malfunction inside the compressor.