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Air continuously leaks out of the unloader valve on your air compressor, and this is a problem…. why?
Well, if air continuously leaks out of the unloader valve, then the compressor tank is emptying, and the compressor needs to restart to replenish the air in the tank to get back up to cut out pressure so it can stop on its own. But then, before you get to use any air, it’s all leaked out again, and the compressor restarts to fill the tank again.
Or, in some cases, compressed air can be bleeding out as fast as the compressor can pump it, and this leads to overheating of the compressor motor and other issues you would rather not have to deal with.
First though… where is the unloader valve.
Where is the unloader valve?
Let’s identify where the unloader valve is on a typical reciprocating air compressor. The unloader valve might be inside of, or attached to the outside of, the compressor pressure switch.
In the photo above are two popular compressor pressures switches. You cannot see the unloader valve on the Condor switch on the left as it is internal, and the air line to it is plumbed into the bottom of the switch.
You can see where the unloader valve and air line from the pump head connects to the Lefoo switch on the right in the photo above. The brass fitting on the left side of the Lefoo switch is the air line connection, and under it is the unloader valve.
Where is the air leak?
Since the Condor pressure switch has an internal unloader, if air is leaking from it, it may be blowing out any opening in the switch cover.
On the external unloader, you can feel the leaking air around the unloader valve itself.
Why is compressed air leaking out of the unloader valve?
If you have read the page providing detailed information about the unloader valve workings found under Air Compressor Information in the right navigation bar, you will know how the unloader valve functions. No need to repeat all that information here, except to say that if the unloader valve is working properly there will be a burst of air from it (1-2 seconds at most) when the air compressor reaches cut out and stops. After that air should stop blowing out of the unloader valve or pressure switch.
If air continuously leaks out of the unloader valve when the air compressor is running, that indicates that it is the unloader valve itself that has failed, and it needs cleaning and / or replacing. If you cannot resolve the leak by cleaning the unloader valve (which may be more trouble than it’s worth to attempt) then replace the pressure switch and that should include a new unloader valve too.
Is Air Coming Out the Check Valve?
When the air compressor shuts down and unloads, then all the air that may have been trapped over the piston is now vented by the unloader valve. It’s gone. That means that if compressed air continuously leaks out of the unloader valve, the only other place where that compressed air might be coming from is the air tank itself.
What is supposed to keep the air in the compressor tank when the unloader valve is open? The tank check valve. (Detailed information on the tank check valve is found under Air Compressor Information in the right navigation bar).
If air continuously leaks out of the unloader valve when the compressor is not running, then your compressor tank check valve has either failed completely, or the internal seal has not seated properly and this is allowing air from the tank to blow by that seat and escape out the unloader valve which, when the compressor is stopped, is open to atmosphere.
How to fix it?
In order to stop the air leak out of the unloader valve you will want to…
1) Unplug the compressor
2) Drain all the air from the tank
3) Remove the lines connected to the tank check valve
4) Remove the tank check valve, inspect, clean, re-install the same one, or install a new one
5) Reassemble and test the compressor operation. If the check valve is now working, once the compressor unloads at high pressure cut out, air should stop leaking from the unloader valve.
Where do I get a new one?
Even though parts supply for the typical home or small workshop air compressor is always a problem – not too many people that sell this type of air compressor stock parts – you can replace your tank check valve with any vendors tank check valve that fits the thread in the tank and to which you can attach the line to the unloader valve.
Questions about air continuously leaks out of the unloader valve are welcome using the form below.