Craftsman unloader valve is not working

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I am having problems with my craftsman 2 hp air compressor. The Craftsman unloader valve is not working.

When the pressure switch is in the auto position and reaches pressure, the switch hits the unloader valve and drains the tank until the next cycle.

It also hits the unloader valve in the off position and totally drains the tank.

I tried changing the pressure switch which included a new unloader valve and check valve but I still have the same problem.

Do you have any ideas?


The following is an image of Sear 2 HP air compressor.

Craftsman Sears 2 HP air compressor


The unloader valve does not normally drain the tank, Travis.

When the compressor reaches normal cut out pressure and the pressure switch toggles to off to stop the motor the unloader valves job is to open and to drain any air that may be trapped over the piston(s), helping the restart process by removing some of the load on the piston.

Often smaller air compressors have motors that are only marginally big enough to drive the pump, and if there is air over the piston, the motor cannot start properly.

In the case of this air compressor it is not the Craftsman unloader valve that isn’t working. It’s working fine, and opening when the compressor stops which is the job it is supposed to do.

The compressor unloader valve is emptying the tank when the air compressor trips to off is because the tank check valve isn’t closing properly. As a result, all the air in the tank bleeds out the unloader valve, the tank pressure drops to motor cut in, the compressor starts and the cycle repeats.

If you remove, clean and/or replace the tank check valve on your compressor, I suspect the problem will be solved.

By Ashley Pearce

As a passionate manufacturing and mechanical engineer, I've had my fair share of run ins with air compressors and compressed air systems. With over a decade of experience in the industry, I have both a fresh perspective and time-served hands and mind to help you with your compressor problems (along with our able community!)

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