What Is an Unloader Valve Air Compressor?

by Michael Batton Kaput; Updated September 26, 2017

Air compressors are vital to the operation of a wide variety of machinery across a wide spectrum of industries, as well as crucial to safeguarding the lives of employees working in contaminated zones. A main component of air compressors is the unloader valve.


The unloader valve periodically releases pressurized air building up inside the air compressor.


The unloader valve is an integral part of reducing the pressure on the air compressor’s motor during the course of air compression.


The unloader valve can be heard every few minutes when the air compressor stops and a hissing noise indicates air is being released.


Pressurized air builds up inside an air compressor. When the air reaches a set limit, the unloader valve opens and releases the air until the pressure inside the machine returns to an acceptable level. When the engine starts up again, it is under less strain now that the air pressure is released from the machine.


A secondary valve called a check valve ensures that compressed air does not flow out when the unloader valve activates. This check valve can fail, resulting in a continuous hissing as the unloader valve continuously releases air.

About the Author

Michael Batton Kaput began writing professionally in 2009. He is an editor at two magazines and a freelance writer. He has been published in "Egypt Today," Egypt's leading current affairs magazine, and "Business Today Egypt," Egypt's number one English-language business magazine. He attended Denison University where he earned a degree in political science and English literature.