What happens if the outlet valve of the compressor is closed?
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Could it keep running for another 3-5 minutes, like a pump? In that case, the outlet temperature will be high—so high that shutdown occurs as a result of the interlock. What harm might this cause to the compressor? Let’s discuss it.
1. Interlock shutdown due to high pressure in the reciprocating machine. 2. Interlock shutdown due to high temperature in the centrifuge
When the pressure is high, it will automatically switch to two-in-one mode. Our system only has a high-pressure alarm; there’s no interlock mechanism. Is this acceptable?
It is not allowed to close the outlet valve of a compressor, even in the case of centrifugal compressors. If the outlet valve of a reciprocating compressor is closed, pressure buildup will occur. Generally, compressors are equipped with interlocks related to the outlet temperature and lubricant pressure; allowing pressure buildup can damage the equipment and, in severe cases, cause injury to people, so such behavior is strictly prohibited. In the case of centrifugal compressors, interlocks are established between oil pressure and parameters such as shaft displacement or dry gas seals. Generally, these types of compressors have a high flow rate, and the buildup of pressure due to large amounts of airflow can cause severe damage to the internal components of the compressor, which is strictly prohibited.
If a safety valve is installed at the outlet of a reciprocating compressor, it will activate. Centrifugal compressors can cause surge. There is a difference between gases and liquids, and it is very dangerous to have pressure build up at the outlet of a reciprocating compressor. It is essential to take precautions to prevent accidental operations; one such measure is interlocked shutdown. One is to open two and return one. Also, the outlet of the centrifugal compressor must be equipped with an automatic return mechanism. It’s all to prevent accidental operations
If the outlet valve is closed, the best outcome is that the compressor shuts down due to high outlet pressure interlock. If the interlock fails, it can cause problems for the reciprocating machine; in the best case, it may damage the air valve, while in the worst case, it could deform the cylinder or bend the piston rod. And the centrifuge may have burned out the bearing shells. Or damage the turbine shaft.
When the outlet valve of a centrifugal compressor is closed, the safety valve at the outlet will definitely activate first; it’s fine to let it operate for a few minutes.
The safety valve trips, triggering the interlock protection mechanism
If the outlet valve of the compressor is closed, the machine will vibrate; when this vibration reaches a certain threshold, the solenoid valve controlling the speed control oil loses power, causing the machine to stop.
First, the anti-surge valve opens (as the unit does not experience vibration during normal operation), then the safety valve at the compressor outlet activates (as the pressure at the compressor outlet continues to rise). Finally, the unit shuts down due to high vibration amplitude (as the flow rate and pressure continue to be mismatched, causing increased vibration).
If the interlocks that are supposed to function do not activate, the outlet of the reciprocating compressor will experience severe over-temperature in a short period of time, and the centrifuge will suffer from surge; over time, this can lead to damage to the machine components!