The minimum pressure valve is also called the pressure holding valve, which guarantees the life of the minimum pressure of the oil separation tank. The minimum pressure valve will open only when the pressure of the oil separation tank reaches a certain pressure value.
The minimum pressure has a command function, and the rescue of the oil separation tank is prevented during unloading and shutdown.
We need a minimum pressure to circulate the oil. Circulation of oil is critical for cooling the rotary screws and for the lubrication of the bearings.
A rotary screw compressor has no oil pump. The oil is pumped through the system by the differences in pressure that exists inside the compressor.
When the compressor just starts up, we need to build up pressure as soon as possible, for the above reasons.
If the compressor is connected to an empty air receiver or piping system then it would take a long time before pressure is built up (a very long time). Therefore, the minimum pressure valve stays closed until a minimum pressure has been reached inside the air compressor. That minimum pressure is usually around 4 bar.
As I said earlier, the minimum pressure valve also acts as a check valve. This is to make sure that no air can flow back into the air compressor.
If you experience too much oil carry-over (oil in your compressed air), it could be due to a bad minimum pressure valve.
If the minimum pressure valve is malfunctioning, there will be a ‘rush’ of compressed air blown through it at startup. The separator element will not function properly at these high flow rates and low pressure.
The minimum pressure valve will prevent a portion of a pressure system from dropping below-set minimum pressure. Initially, as inlet pressure builds, the valve will open at a preset opening pressure allowing pressure to build throughout the system. When the pressure at the outlet is reduced enough, the valve closes to maintain pressure at the inlet. An independent check valve prevents backflow.
