Dumb question on air compressors.....

[Samckitt]

I just got a 30 gallon Craftsman one on Saturday. Basically for free, the neighbor guy was driving by & stopped to talk to my about the motor for the Monte & I saw this compressor in the back of his truck. He was taking it to the dump because it would only go up to 40psi & not hold any more air. He changed the pressure switch to a Square D one (obviously didn't make a difference because it just keeps running & running). I said can I have it & let me jack with it for a while? So I got it. Took it apart & found a broke reed valve, replaced it for $33 & now it works fine.

So I have a question. On the pressure switch, when it is compressing air to the tank, there is a little pressure relief valve on the switch that is closed. Once the pressure is reached & the pump shuts off it triggers this relief valve to let air out of the tank until it gets low enough that it kicks back on. And the cycle repeats.

So my dumb question; why have the relief valve when it isn't running if it just lets air off until it kicks back on?

[rivs68]

Sounds like the pressure switch is set too high. I believe the "relief" valve is an over pressure safety...So the pressure switch needs to shut off before the relief trips...The switch should have an adjustment nut on it...

[Samckitt]

The relief valve is opened by the same arm that turns the motor off. When it kicks off, the arm pulls the contacts off so the motor shuts off, when this happens it pushes a little pin down in this valve to let the air out of the tank. Once it gets low enough it kicks back on & the valve shuts.

[Samckitt]

https://static1.pt-content.com/images/noimg.gif

In this image, on the bottom left side you can see the flat part of the arm that pushes the valve open, that is the same arm that pulls the contacts open to stop the motor.

[Samckitt]

UNLESS! The guy that had it, jacked with the adjustment nuts that control that arm...... OK Gotta go investigate more......

[Samckitt]

Nope, all the same arm like I originally thought.

[Kenova]

That little relief valve releases the pressure between the compressor and the check valve. It does this so the motor isn't required to overcome any pressure in the line making for an easy start for the motor. If this valve is still releasing pressure after the motor stops, then it is on the wrong side of the tank's check valve or the check valve is defective.
There should be some sort of adjustment available to raise or lower the pressures at which it starts and stops. Check the label on the inside of the switch cap.
I just spent the better part of a day jacking with my 20 gal Campbell Hausfeld. New pressure switch and regulator. Starts, runs and just plain works better.

Ken

[Samckitt]

Ah Grasshopper, that makes sence. I am guessing that the check valve is bad. Because it keeps going and going and going and......

[Happyfunballs]

I'll add that when you rebuild it(assuming that it's oilless) parts can be difficult to find and a bit pricey. I rebuilt my Craftsman compressor twice before giving it to my brother-in-law. Plus it was loooooud.

[Tony_SS]

I'll add that when you rebuild it(assuming that it's oilless) parts can be difficult to find and a bit pricey. I rebuilt my Craftsman compressor twice before giving it to my brother-in-law. Plus it was loooooud.

Ditto.. my old oiless Craftsmen was too loud.. my Dads "professional" model is nice and quiet though.

[Samckitt]

Agree it is noisy. But it was given to me so I will take it.