Definition

• An air compressor unloader, which takes the form of a valve, opens based on a set pressure limit and releases air into the atmosphere. Unloader valves are typically included in the pressure switch assembly and are positioned between the receiver and compressor lines.
  
  

Pressure Switch

• The pressure switch in the assembly reacts to pressure in the air compressor system. Various levels of pressure prompt the switch either to turn on or off the compressor motor. The compressor motor, when switched on, opens the valve and closes the valve once shut off.
  
  

Problems

• Air evacuating from the valve is indicated by a hissing noise. Constant hissing throughout the air compressor operation typically indicates an air bleed. This air bleed is often the result of a failed check valve, which prevents compressed air from flowing back out into the system. Under such circumstances, replacing the check valve often corrects the problem.