Craftsman 125 psi air compressor dumps air too soon.

When you turn it on it will get up to 40 to 65psi and then release the air like it is full.





Bill answers...

Howdy, and thanks for writing in.

I am understanding that your compressor "releases the air" at 40-65 PSI out the same place as it used to when the pressure got up to the normal cut-out pressure... 150 PSI or so?

When the compressor reaches normal cut-out pressure, the pressure switch trips off, cutting the power to the motor and stopping the compressor.

At the same time (usually) that same tripping off opens the unloader valve, which dumps the air trapped over the piston. This allows for an easier start next time your pressure switch trips back on.

In your case the unloader valve is opening at a much lower pressure than desired, and that leads me to believe that your pressure switch is tripping the unloader valve prematurely.

That being the case, changing the pressure switch would be your answer.

Before you do that, take your unloader valve apart and put it back together again, making sure that the moving parts in it actually do so. If the unloader valve isn't the problem, your pressure switch is.

Cheers,

Bill






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Craftsman 125 psi air compressor dumps air too soon.

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Aug 17, 2009
 Unloader, pressure switch or pressure release valve?
by: Anonymous

You say "dumps air" but not a word about how or where.

Your problem could be one of 3

1.- Pressure release valve
2.- Unloader
3.- Pressure switch

1.- There is safety a pressure release valve, that simply blows air when pressure gets too high, protecting everything from dangerous high pressures, this valve is made from a bronze body with a steel ball covering an air release hole held by a spring that can sometimes be adjusted within certain range, in other types there is no adjustment, and if it blows the pressure too soon (at a too low pressure) it has to be replaced, make sure that you replace the valve with an identical one because if you use a safety release valve with a setting too high it can lead to a dangerous condition.

2.- Unloader, there are many types of unloaders, those devices basically release the pressure from the compressor cylinders as soon as the electric motor stops, so when its time for the compressor to start again, the motor will not be working to spin up the compressor loaded with whatever the pressure is in the system when it starts.

There are centrifugal unloaders, which can be really complicated and are used in high end industrial compressors, too complicated...
And there are the simple ones, they are integrated in the pressure switch, when the pressure switch stops the compressor, it pushes a little shrader valve, like the one in your car tires, and releases the pressure in the compressor heads, the way they normally fail is that they keep leaking air continuously, and keep the compressor cycling every few minutes, even if you are not using the compressed air.
The same moving part that has the lever that pushes the electric contacts pushes the shrader valve.

3.- Pressure switch. it's a little box ( 2 by 3 by 3 inches aprox) with a nut in the top of the box that releases the cover, easily recognized by its connection to both air and electric parts of your compressor.
when you remove the cover there are a few wires inside and usually in the same long screw that protrudes through the box top to hold the cover, inside, there is an adjusting nut the allows to adjust the cutoff pressure of the switch, there are 2 different types, with fixed differential, (the pressure difference between off and on) and adjustable differential. usually inside the pressure switch cover there are instructions on how to adjust the cut-off and differential pressures.

So first identify what your problem is and then try to fix it.

______________________

A comprehensive response, and I very much thank you for your contribution.

Cheers,

Bill

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