Reaches 125psi shuts off and blows air out of the valve attached to the tank

by Darin
(Seattle)

My compressor reaches pressure, kicks off and depresses a release valve in the LF 10-L4H switch that is attached to the tank by a tube. It gets down to 80psi and kicks back on again. I have to manually pull the plug and push down the adjustment bolt.

I replaced with a brand new switch and it worked for a year and a half. Started again doing the same thing, this time the new switch I installed has the same issues as the one I replaced.

When the cover is on, it has a push pull red button. If at anytime that button is pushed, it turns off the compressor and releases the pressure... it is the same valve that hisses when it turns off after reaching pressure of 125.

thanks

D

_____________________
Bill says...

Darin, from what you have described, I don't think your compressor has a pressure switch problem, so much as a check valve issues.

Please visit the site map page, and read the page on Unloader Valves, Check Valves, and Unloader Valve Leaking for more info.

If the information there doesn't help, please post a comment here telling me what you found, and we'll press on.

Cheers,

Bill




Comments for
Reaches 125psi shuts off and blows air out of the valve attached to the tank

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Dec 31, 2011
 Unloader valve
by: Darin

It is the unloader valve, that is draining the air all the way down to 85psi, at which point it kicks on and fills up to 125psi, at which point it kicks off and bleeds down to 85psi. On a Brand NEW pressure switch.

"First, What The Unloader Valve Does
The unloader valve is a needle valve which is linked to, and responds to the pressure switch as the switch reacts to the compressor tank pressure. The mechanical action which opens the contacts inside the switch to shut off the compressor motor, is linked too, and also opens, the unloader valve. This unloader valve then connects the compressed air trapped over the compressor piston to atmosphere, and allows that trapped air to escape, unloading the compressor.

You can hear this happen. When a compressor reaches the high pressure set point and stops, there is the characteristic "Psssssst" sound, the sound of air escaping. This is the sound of the compressor pump being unloaded. And it should be a brief burst of air, normally less than a second or two."
Dec 31, 2011
 do not believe your compressor problem has anything to do with the pressure switch
by: Anonymous

"If air is bleeding out of the unloader valve when the compressor is running,
A bum or dirty check valve is a possibility,

I do not believe your compressor problem has anything to do with the pressure switch. I suspect your problem will be solved if you remove, clean and replace the tank check valve."

It is when the compressor is OFF, when it shuts OFF, when it reaches 125psi and the switch opens the contacts..at this time depressing that valve. My brand new non rusty, non dirty, completely clean brand new switch pushes down on that valve in the OFF position. IF I unplug the unit before it gets to 125psi, NOTHING leaks, Tight as a drum.

I've tried adjusting the cut in/cut out, on this switch, (brand spanking new switch, not dirty not fouled by grease oil or rust) it is a bolt inside a spring, turn it to the right and it increases the values, turn it to the left it decreases the values. It did not help any.
Dec 30, 2011
 valves and compressor
by: Darin

Ps. there are 3 valves on my compressor... one is a safety valve on the tank, the other is in the pressure switch, maybe this is what you say is an unloader valve, the other is a stopcock at the bottom of the tank to drain the condensed water and oil occasionally... I'm not grasping your useage of the check valve.

This is my compressor, very similar to mine.
http://www.harborfreight.com/25-horsepower-21-gallon-125-psi-cast-iron-vertical-air-compressor-67847.html

________________

Darin, the valve beside the pressure switch is the unloader valve. Please read the unloader valve page to better understand its purpose.

If air is bleeding out of the unloader valve when the compressor is running, either the unloader valve isn't shutting off (stuck??) or the check valve inside the fitting where the air line from the pump head to the tank is plumbed, is not sealing properly, and air is bleeding back out the unloader valve.

A bum or dirty check valve is a possibility, even on a new compressor.

I do not believe your compressor problem has anything to do with the pressure switch. I suspect your problem will be solved if you remove, clean and replace the tank check valve.

B.
Dec 30, 2011
 The switch is New it is an LF10-L4H
by: Darin

It is an LF10-L4H (http://www.toolmarts.com/interstate-pneumatics/IP-LF10-L4H.html)

It is 100 percent brand new and if you look at the link and the picture, that little brass compression nut, is a plunger like valve that gets pushed down and Open when my compressor reaches 125psi it shuts off which drops a lever that depresses that valve and lets the air out till it gets down to 80-85psi then it kicks back in again... cycling over and over if I don't go and pull the dang plug out of the wall. This happened a couple years ago, I got a new pressure switch, replaced it and it worked fine... now doing the same thing... so I got a NEW CLEAN UNUSED switch and replaced the one that leaks and it has the same problem.
Dec 28, 2011
 valve or switch or switch valve
by: Darin

Hi
I probably did not describe well enough.

On the pressure switch, the thing that has electricity running to it and there are contacts that turn off and on the motor. There is a valve that can release air when I turn off (push the red button down), this valve has a tube attached to it with a compression nut, this tube goes into the tank.

There is a separate "safety release" valve on the tank that blows if the tank pressure goes over 125psi, this one does not leak, unless I pull up in the pin.

The compressor cycles on at 80 off at 125, it kicks on, reaches pressure of 125 then kicks off, and blows air out of the little plunger valve attached to the pressure switch, until it hits 80psi then kicks back on again. This is a new pressure switch, the LF10, it is just like the pressure switch I replaced a year and a half ago. It worked up until a week ago.

_________________________

"There is a valve that can release air when I turn off (push the red button down), this valve has a tube attached to it with a compression nut, this tube goes into the tank." I believe that this is your unloader valve, not a safety valve at all. I also believe that your pressure switch is a Condor, is that correct?

I believe your check valve is leaking. Pull it an clean it or replace it and this should solve the problem.

B.

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