Reciprocating compressor fault diagnosis
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There is one issue regarding the diagnosis of faults and the disassembly/inspection of valves that I haven’t been able to figure out. For example, if the exhaust pressure at the first stage of the compressor is low, experienced technicians simply decide that it’s sufficient to open the exhaust valve to check for leaks. I understand that it’s probably a leak in the intake valve. The piston draws in air normally during compression, but due to the leak in the intake valve, the pressure is low during exhaust. The exhaust valve should be open during compression anyway, so even if there’s a leak, it shouldn’t cause any problem. I don’t understand why, during maintenance, they only check the exhaust valve – could someone please explain this to me? Thanks!
In normal operating conditions, the exhaust pressure of a reciprocating compressor is fixed. Personal experience in production: a leak in the intake valve directly affects flow rate, while a leak in the exhaust valve directly affects pressure
One cycle of operation for a reciprocating compressor consists of expansion, intake, compression, and exhaust. The exhaust valve opens at the end of the compression stage, with the opening pressure determined by the back pressure in the pipeline and the force of the valve spring. Leakage in the exhaust valve, damaged valve plates, or broken springs generally cause the valve to open prematurely, affecting the exhaust pressure
It can be understood in this way: a leaky exhaust valve means that the exhaust pressure has not yet reached the level at which the exhaust valve opens, as a result of which the exhaust pressure remains low. As for a leaky intake valve, apart from the gas that escapes through that valve, some gas also escapes through the exhaust valve once the exhaust valve reaches its opening pressure.
If it is multi-stage compression, it’s not necessarily the case
It’s just like a pump: if the exhaust valve leaks, gas escapes back, and as less gas flows through, the pressure drops
Damage to the valve discs or springs of the intake and exhaust valves can affect the corresponding intake and exhaust pressures. Fluctuations in intake and exhaust pressures: It is necessary to check for any damage to the intake and exhaust valves, as well as to examine the stability of the oil pressure.
The leakage of the exhaust valve also directly affects the flow rate.
If the outlet pressure is low, how to check it depends on the condition of the compressor. If it is multi-stage compression with air being sent from one stage to the next within the system, then both the inlet and outlet valves need to be checked, because when the air supply flow rate from the previous stage does not meet the requirements, the suction force of the subsequent stage can cause the pressure at the outlet of the previous stage to drop. If it is sent outside the system, then its pressure is determined by the system, that is, the so-called back pressure. Theoretically, it should not cause any change in system pressure; in practice, however, a decrease in flow rate leads to a drop in system pressure.
It is multi-stage; the reason is that the pressure at the secondary inlet is higher than that at the primary outlet. Therefore, it was assumed that there was a leak in the exhaust valve. After disassembling it, it was found that the valve was fine, so it was speculated that the issue might be caused by dirt in the buffer tank at the primary outlet