When it runs the air keeps running out of the unloader valve.

by Ronald Norris
(Altoona, Pa.)

I wanted to make a "silent air" compressor out of my HF oil compressor. I took off the original (new) motor and replaced it with a motor/compressor from a fridge, so far so good.


When it runs the air keeps running out of the unloader valve. I tried to do this to 2 new compressors (oil) and still the same thing, I got no air in the tank. I gave up on the oil compressors.

I bought an oil free one, took off original motor hooked up the fridge motor/compressor. Started no problem but the compressor wouldn't shut down at the 100 lb. mark it kept running. Also there was an awful high pitch sound coming from the area around where the air enters the tank.

I taped around the threads and it still did it. I really need a "silent air' compressor because I do t-shirt airbrush work and I just got people that moved in below me about 1 month ago so I can't use any compressor now. Oh, I checked the tank valve on the oil compressors they seemed to be okay. Also checked the unloader valve actuator valve pin, seems to work. Need help!!
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Ronald, your concept of using the refrigerator compressor is brilliant. A small (joke) company called Jun-Air built an empire doing basically what you are doing.

From what you are telling me, I suspect that the tank check valve is not working. It's supposed to keep the air in the tank when the unloader trips to dump the air over the piston when the compressor stops. If the check valve is failing, tank air bleeds out of the unloader valve. That it's whistling suggests that the flap hasn't seated all the way.

Cheers,

Bill

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Jul 15, 2015
Exactly same problem.
by: jones

hi, i too have the same problem. check valve no problem, pressure switch no problem. was tested ok on the old motor. but after i connect everything to new fridge compressor, it just leak all the air when i turn on the compressor.

Jul 14, 2015
Fixed it !!!
by: Julien

Hi,

Got it figured out !!!

As i was saying in my previous comment, there is a very small spring into the unloader valve.

This is what makes the unloader valve bleeds continuously at motor start (as there is no pressure in the unloader valve). As the pressure raise, the pin gets in and closes slowly.

You did not noticed it with the old motor, because the pressure raise much faster than with a fridge motor.

To fix this, you have to remove this small spring.
That way, the pin will close immediately after you start your motor.

I did it this morning and finally (after 2 months of thinking, research, opening, reopening), it works.

I had to use a needle and made a hook at the end of it... caught the spring and took it away

ps: The check valve had nothing to do with it and the pressure switch was perfectly fine.

Julien

Jul 13, 2015
Compressor unloader leaking
by: Bill

Julien, typically the unloader valve is not supposed to leak air when the compressor is pumping air into the tank.

It makes no sense that the unloader requires tank pressure to close.

This thread is now complicated as I have no idea what type of compressor we are talking about, and different compressors have different unloader mechanisms, some of which are open all the time.

I suggest you start a new thread and upload some photos of the pressure switch and your compressor so we can see about which you write.

Jul 13, 2015
have same problem with leaking unloader
by: julien

hello,

this post is quite old but i would be interested in knowing how you fixed your issue.

I have the same issue. I want this very noisy compressor air (95db) to run silent and from my research, replacing the motor with fridge compressor should do the trick (as far as i could see on youtube).

I have a completely new check valve and pressure switch but still once the fridge compressor starts, the unloader valve bleeds air.

From what i could see, my check valve is ok.

So i have disassembled my pressure switch to check the unloader valve.

Interesting..., there is a very small spring which prevent the pin from closing. That is why the unloader keeps bleeding air. I suspect that a minimum pressure is needed for the unloader valve pin to close (between 2 & 3 bars).

I could check this theory on a compressor with the old motor. The unloader valve bleeds air until the tank hits between 2 & 3 bars.

What do you think about that? Is it the unloader valve that is not operating as it should?

Thanks

Aug 12, 2012
Unloading valve
by: K4

Hi bill,
Thanks for the reply, answer to your question is yes all works fine with the original compressor, check valve is fine

Is it safe to get rid of the unloading valve? By removing the tube between check valve and unloading valve and I will block the gap on check valve?!

Thanks for your time
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It is not a question of safety, just whether or not your air compressor will start with air trapped over the piston, which will happen periodically when the compressor stops after reaching cut out.

If the unloader valve is leaking air when the air compressor is running, either the pressure switch did not shift the unloader valve to close when it turned the compressor on, or the unloader valve itself is stuck open.

B.

Aug 12, 2012
Same prob
by: K4

The very same problems , got a new compressor works 100% and I replaced it with aircon compressor and it seems as I run compressor the unloading valve leak or stay open???

Could it be the amount of air going in is not triggering to close valve? Please help
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Are you certain that the connection between the pressure switch and the unloader valve is there, or working?

Once air gets into the tank the pressure building shuts the tank check valve. When the compressor stops, that air pressure (it doesn't take much) prevents the compressor tank air from bleeding out the unloader valve which remains open while the compressor is off.

If air is bleeding out of the unloader valve while the compressor is running, then either the unloader valve did not shut when the compressor started (this happens when the pressure switch trips to on) or the tank check valve is leaking.

B.


Apr 23, 2012
Question about an answer from Bill for Bill
by: ronald norris

From what you are telling me, I suspect that the tank check valve is not working. It's supposed to keep the air in the tank when the unloader trips to dump the air over the piston when the compressor stops. If the check valve is failing, tank air bleeds out of the unloader valve. That it's whistling suggests that the flap hasn't seated all the way.

BILL why would this do this on 2 new compressors also when I put the original motor back on the oilless comp. the whistling stopped so I can't see how it could be the flap not seating. Your advice or any ones advice greatly appreciated. The motor/compressor that I used squirted some oil into the system would that have anything to do with anything?
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Ronald, it is either the check valve is not seating, or the unloader valve itself is stuck open. If the air is bleeding out of the unloader valve, it can only be one of these two things.

When you say "The motor/compressor that I used squirted some oil into the system would that have anything to do with anything?", not knowing where the oil went, I can only suggest that oil being where it is not supposed to be is not good anytime.

B.

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Unloader valve

by Pete martinez
(San tan valley,az)

I have a 919.167310 6hp 30gal craftsman compressor that wont restart at cut in time and pops breaker. I have replaced pressure switch with one i had found at a True Value close by. What else am i not seeing?

_____________________
Bill says...

Pete, your pressure switch turns the power on and off to your compressor, and, depending on the switch type, either toggles internally or externally an unloader valve.

One common problem for compressors popping breakers on restart is that the unloader valve isn't dumping air over the piston on compressor shut off.

Id your unloader valve working?

Cheers,

Bill

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