yet another leaking air compressor question


  #1  
Old 12-18-07, 10:41 AM
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yet another leaking air compressor question

I've got an old Emglo Air-Mate 1 1/2 HP, model #AM78.

The problem is the pressure release valve. After cycling, the valve is suppose to shut off after a few seconds. And sometimes it does. More frequently, however, it sticks open and lets a constant *pssssshhhhhttttt* of air out. (like the sound effects?)

I took it into the repair shop last year, got it back, they had replaced the entire pressure switch, part #5131501-00 (which comes with a new pressure release valve mounted to the body) but it still intermittantly did the same thing.

It makes me wonder if my tanks are just so dirty and rusty inside that the junk in the air is plugging something up. Doesn't make me feel good about my guns either.

addendum:

I did find this info on a repair site... 16A unloader valve: #PS2020RV "This is located on the side of the pressure switch. If your valve is attached to your switch by inserting through a hole on the side bracket, then this is your style. Order this if your valve is broken. If this valve leaks continuously after it shuts off, then don't order this, order a check valve on the check valve page. It backfeeds this valve when defective giving a false sign that this needs to be replaced."

Maybe I'll figure this out yet. ???

another addendum:

It seems like the check valve they are referring to above is the one that is connected to the tank. When the compressor runs, the valve opens, allowing air from the check valve to enter the tank (or the other way around) through a tiny supply hose. It seems that this check valve (looks like a 3/8" brass nut with a needle-like bleeder valve in the center of it) may not be seating properly when the compressor shuts off, allowing a bit of air through, creating the problem.

I've messed with it a few times and it seems to be acting better.
 

Last edited by XSleeper; 12-18-07 at 11:45 AM. Reason: self-editing
  #2  
Old 12-18-07, 12:45 PM
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I don't know if this would apply to your situation but I used to have problems with my portable compressor in the winter. If it got below freezing in my van overnight, the next morning the pop off valve would leak until the unit warmed up.
 
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Old 12-18-07, 03:04 PM
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It is possible that their hint is the problem.
How you can "check" the check valve is to first allow the compressor to build up pressure and then unplug it.

The *pssssshhhhhttttt* should shortly stop.
If the air continues to escape then the check valve is leaking.

If the check valve is working you should be able to remove the discharge line from the pump end and no air should escape from the tank.
 
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Old 12-18-07, 03:32 PM
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Yeah, I'm 100% sure that bleeder inside the check valve is the problem. I took it off, soaked it, blew it out, and it seemed to work well after that.

I also took the pressure switch off, took it apart, and I'm glad I did. The air housing was partially blocked up with rusty dirty gunk. I can only imagine the tanks are the same. I think I'll be running an inline filter on this compressor from now on to protect my tools.
 
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Old 12-19-07, 08:24 AM
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Sounds like you are getting a lot of blow-by, which carbons up your valves and lines. If you value this compressor, it may be time for a cleanup and a new set of rings.
 
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Old 01-22-08, 03:42 PM
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GregH,

I got my compressor out again today (for the first time since I worked on it) and it was doing the same thing again. So I went to the service center to get a new bleeder check valve, but they were out of it. The tech told me something interesting that I didn't completely understand- maybe you can enlighten me...

He said there's about a 5% chance that the bleeder check valve is bad- he said it is more likely that something inside the head is gunked up and it's not creating enough pressure to pull the bleeder check valve shut.

Does this sound reasonable? If so, what needs to be cleaned out in order for the bleeder to shut? It continues to *pssssshhhhhttttt* after the compressor shuts off, both from the bleeder valve and from the back of the pressure switch (it said online that the bleeder valve leak is what also creates the leak at the pressure switch).
 
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Old 01-22-08, 06:31 PM
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His explanation makes no sense to me.

The check valve will be located on the air tank to stop the reversal of flow from the tank to the compressor head when the pump stops.
It is the pressure in the tank that forces the check valve closed.

How does this fit in with what the parts guy said???

Maybe the parts guy was thinking about some other type of compressor or I don't understand what you have.

Is the check valve mounted at the tank?


A couple of pics posted to Photo Bucket would tell us exactly how your compressor is put together.
 
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Old 01-22-08, 07:19 PM
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Well it didn't quite make sense to me either. I thought the check valve was supposed to close against pressure, not need pressure to close.

What I've got is an old Emglo Airmate, model AM78 HC4V.


Yes, the check valve is mounted to the lower tank (it's a 1 1/2 HP stacked twin tank model) and it has a black nylon hose that comes off at a 90 degree angle and heads up to the unloader valve / pressure switch. A copper line from the compressor head attaches to another port.

I can't find a schematic online, but it's similar to part #8, pictured HERE.

Or part #19, pictured HERE.

When I cleaned the "check valve" previously, I believe I was only cleaning the cold start valve (spring loaded needle and seat inside a 3/8" nut). I guess I should have taken apart the entire check valve, because I bet there's gunk in it. For some reason I thought it was just a brass elbow.
 
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Old 01-22-08, 07:38 PM
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Ya, you could try cleaning it and if that doesn't work the addendum in your first post suggests you replace it.
 
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Old 01-22-08, 07:55 PM
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OK, I'm pumped up to try this. Now to brave the cold... get the thing out of my pickup, and bring it in where it's warm!!!
 
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Old 01-22-08, 08:19 PM
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Yeah I think it needs to be replaced. The spring loaded plastic seat seems to have a rubber seal on it that's completely worn off, and it's leaking air out the pressure release valve something terrible.

Thanks for all your help- I'll hit the Dewalt service center tomarrow.
 
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Old 02-15-08, 07:09 PM
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Just a followup...

I found a place online that could get me replacement parts at about half the cost of the Dewalt service center so I gave them a try. The first order arrived with the wrong check valve, but after much consternation, the right part finally arrived...

...and the compressor works like new! Yay!

Thanks for all the advice.
 
  #13  
Old 02-15-08, 07:23 PM
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Glad it worked out
 
 

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