The solution here is to check and clean the unidirectional valve, replacing it when necessary. Improper installation or blockage of the oil return pipeline will impede the normal return of the lubricating oil.
[pdf] Choosing the optimal oil for your screw compressor should consider various factors: Manufacturer specifications: Always consult the manufacturer's recommendations regarding viscosity and oil type. Operating conditions: Evaluate ambient temperature, duty cycles, and typical compressor loads.
[pdf] When the inlet/unloader valve is open, the air enters the compressor screw element. The screw element works like a pump and it compressed the air. During this process, oil is injected in the element. The oil is there to cool the air, as the air gets very hot during compression.
[pdf] 
