A pressure relief valve is a safety device designed to protect the compressor from over - pressure situations. Its primary function is to open automatically when the pressure inside the compressor reaches a pre - set limit, allowing excess air to escape and reducing the pressure back to a safe level.
[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] As a kind of friction clutch that uses compressed air as manipulating power source, pneumatic-tyred clutch is widely used in such equipment as oil drilling rig and workover rig, and is also an important part of the drive systems of oil drilling rig and workover rig.
[pdf] 
