How To Fix an Air Compressor Unloader Valve

Air compressors are handy for DIYers to have around the house. Having one opens up new possibilities for expanding your tool kit since they’re used to operate nail guns, paint sprayers, inflators and more. However, like most power tools, even the most reliable air compressor will likely need repair occasionally.

One of the most common repairs for an air compressor is when the unloader valve stops working. Fortunately, it’s also a fairly easy fix that doesn’t require a lot of time or experience to address.

What is an unloader valve?

The air compressor unloader valve is what makes the “psssssst” sound when the motor shuts off after reaching operating pressure. When it does that, it’s venting the residual pressure from the compressor head so the motor doesn’t have to work as hard on the next startup.

When the unloader valve isn’t working properly, you won’t hear that telltale sound of compressed air blowing out of the tank when you turn off the compressor. If your air compressor starts up fine on the first start of the day but stalls and makes a loud humming sound on subsequent tries, you’ve got a bum unloader valve. Another sign of a faulty valve is general inconsistency in your compressor’s performance.

The air compressor unloader valve is usually built into the pressure switch assembly, though it’s sometimes found on top of the switch. Contact the air compressor manufacturer to buy a new assembly. Or, remove the cover from the switch (unplug the compressor first) and locate the pressure switch part number. Then, search the web for a replacement part. After that, you’re ready to replace it. Here’s how to do that.