Compressor Switch/Bleed-off Valve Malfunction

ssjones · Nov 8, 2009

Folks:
I am having an issue with my relatively new, 21 Gallon Upright Harbor Freight compressor. The unit is about a year old, but only seen light use.
Last month, it wouldn't start and sounded like it was straining, so I immediately shut it off. I pulled the motor cover and found two motor screws had backed out, into the cooling fan blade. This was the straining sound I heard. I put the two screws back in place, checked the others and fired it up. The unit started right up and filled the canister to 125 lbs of air, as normal. As the motor shut down, a small brass bleeder type valve in the switch popped up, releasing all the air. At 90 lbs, it started running again, but it constantly releases all the air. I fiddled around with the two adjustment screws, one of which is a plastic screw in the plastic switch housing. I screwed it down too tight, breaking the end of the plastic housing.
I ordered a replacment switch on Ebay, and it was identical to the OEM switch (Harbor Freight was back ordered on the switch for several months).
I put the new switch in, and the same thing happens, as soon as it hits 125 lbs, that bleeder valve releases all the air.
Here's a picture of the top of the switch, showing the two screws:

Here's that bleeder valve built-in to the switch housing. It's directly under that brass union nut:

Does anyone know what is causing this bleeder valve to release? It never did this before and would hold air for several weeks.

Torque1st · Nov 8, 2009

It sounds like you may have a bad check valve. The bleeder valve is supposed to open and release just the pressure on the compressor side of the check valve. The check valve is located between the bleeder and the tank.

Number21 · Nov 8, 2009

Those screws having nothing to do with the bleed off valve, they set the cut in/cut out pressure - be very careful adjusting them.

I have had the same exact issue on two HF compressors. I found that draining the tank completely, and then flipping the on/off switch several times, stopped the issue. It happens again every now and then and I do the same thing to make it stop. I've also had the nut that holds the bleeder valve on back off more than once, and jam itself in there so it stays open. A little lock tite fixed that...

It could also be a bad check valve in the tank...

ssjones · Nov 8, 2009

That valve in the second picture (I'll refer to it as the bleeder valve) has a threaded base and lock nut. It looks like you can adjust the depth. Think that is worth adjusting?

Number21 · Nov 8, 2009

ssjones said:
That valve in the second picture (I'll refer to it as the bleeder valve) has a threaded base and lock nut. It looks like you can adjust the depth. Think that is worth adjusting?

Yeah, that's the one that kept coming off on mine. All it does is hold it down, there is no adjusting.

Torque1st · Nov 8, 2009

The check valve prevents air from flowing back to the compressor out of the tank. This problem has nothing to do with the pressure bleed valve or pressure switch. The check valve is bad, replace it.

Charles (in GA) · Nov 8, 2009

Torque is correct. The bleed valve stays open when the pressure switch is shut off, its just that under normal circumstances, the only air pressure it vents is that trapped in the head of the compressor and the pipe down to the tank. Air continually rushing out of the bleed valve tells us the bleed or unloader valve is working as it is supposed to, but the check valve where the pipe from the pump goes into the tank, is not shutting off.

Charles

zmotorsports · Nov 8, 2009

Torque1st said:
The check valve prevents air from flowing back to the compressor out of the tank. This problem has nothing to do with the pressure bleed valve or pressure switch. The check valve is bad, replace it.

This is exactly the problem. The check valve usually will get a little piece of trash in it and stick open allowing the air in the tank to bleed off and drain the tank. The air is coming out of the pressure pop off valve that allows the 'head' pressure to bleed off after the contactor has opened. This allows the compressor to start up quickly the next time the contactor closes and does not have to fight or 'strain' against the pressure of the tank.

Turn the breaker off for the compressor, drain the tank and remove the line going from the pressure pop off on the contactor assembly to the check valve on the tank and then remove the check valve that is screwed into the tank. Some check valves have a small internal snap ring that you can take apart and clean the seat then reassemble and reinstall. I generally keep a spare on hand at work because it happens every several months or so. I throw the spare in and then disassemle and clean the spare and throw it into the toolbox for next time. Mike.

ssjones · Nov 8, 2009

Wow, thanks guys. Your comments make sense, particularly since the problem continues with two switches. I guess it was just coincidence the issue popped up when the motor bolts worked loose.
The manual refers to check valve as an "unloader valve". This is the problem valve you are describing, right? -

If so, I'll try to order a new one from H-F in the AM. I'll also try to remove/clean mine, as I'm betting they will take forever to get me this part.

Torque1st · Nov 8, 2009

Chinese directions and illustrations can be "strange".... The unloader valve is in the pressure switch, it "unloads" the compressor. Some home/shop compressors have an unloader valve in the compressor head. The check valve is under the the large brass nut on the side of the fitting in the picture. If you take that brass nut off there should be a spring and a valve under it.

ssjones · Nov 9, 2009

Torque1st said:
Chinese directions and illustrations can be "strange".... The unloader valve is in the pressure switch, it "unloads" the compressor. Some home/shop compressors have an unloader valve in the compressor head. The check valve is under the the large brass nut on the side of the fitting in the picture. If you take that brass nut off there should be a spring and a valve under it.

Thanks for the confirmation. I'll clean that this evening and order a back up like zmotorsports uses. (H-F parts seem relatively cheap, if available..)

GreyOwl · Nov 9, 2009

Be sure to release all pressure before you remove that nut.
Charles

ssjones · Nov 9, 2009

Bingo, you guys nailed it. I found this piece of metal on the rubber plug of that bleeder valve:

Wow, what a major hassle for something that would have taken me 30 seconds to fix had I only asked when the problem first occurred. I guess they call that "a lesson".

Thanks again for all the quick replies and good information. My compressor is up and running just in time to start nailing trim in our basement...

ssjones · Nov 9, 2009

Btw, I have to seal up all the various fittings. I used teflon tape, but that's leaking in several spots. I have some Waterpump RTV that I used to mount the new switch. Is that OK or is there a more suitable adhesive?

Torque1st · Nov 9, 2009

I am glad you got it fixed. Regular teflon containing or standard paste type pipe dope is good on pipe threads and widely available at the home box store. Do not use it on compression fittings like the two tubes have on them. Compression fittings work with a metal to metal seal. Teflon tape or pipe dope can make them too easy to tighten and cause the fittings to deform or crack.

ssjones · Nov 10, 2009

Thanks. I went to Lowes and picked up a small tube of Oatey "Great White Joint Compound". I let it sit overnight and it really didn't dry, it's still pastey. One of the extra allen-head fittings on the switch is leaking pretty good. Maybe I'll try that water-pump RTV that I used previously, it dried hard and seemed to seal everything. Dang, I'm getting tired of pulling this thing apart nightly!

Torque1st said:
I am glad you got it fixed. Regular teflon containing or standard paste type pipe dope is good on pipe threads and widely available at the home box store. Do not use it on compression fittings like the two tubes have on them. Compression fittings work with a metal to metal seal. Teflon tape or pipe dope can make them too easy to tighten and cause the fittings to deform or crack.

Torque1st · Nov 10, 2009

Regular pipe dope does not dry. Look for another cause; damaged or bad threads, insufficient tightness, cracks from over tightening, etc.

Consider this a learning experience.

ssjones · Nov 10, 2009

The waterpump RTV worked well, she's air tight now. At least I know where to look now when it happens again. The compressor is over a year old, I should probably drain/fill the oil and get rid of any other debris in the motor.

Thanks again for the help - I would no doubt be scratching my head over the problem if not for your replies & comments.
(note to me: Check here for 1st for garage issues before diving in blind!!!)

Torque1st · Nov 10, 2009

I am glad you got it fixed. Every man cave should have a working compressor. :beer:

RTV generally should not be used for a pipe and fitting sealant but in this case it seems to have worked. Those Asian parts and fittings are notorious for having improper threads.

Did you determine where that metal came from? It may have been a shaving left over from the manufacture of the compressor that took some time to break loose.

ssjones · Nov 11, 2009

Torque1st said:
Did you determine where that metal came from? It may have been a shaving left over from the manufacture of the compressor that took some time to break loose.

My buddy called it "sharf", from improper cleaning during machining or a chip from the casting. It was almost paint-chip thin, the picture makes it look thicker.

Torque1st · Nov 11, 2009

It looked like aluminum swarf to me also. Hopefully it was only the one piece.

Good luck with your compressor. Put it to good use. :thumbup:

Compressor Switch/Bleed-off Valve Malfunction

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