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Old 09-26-2007, 12:20 AM   #1
bmwpower
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Default Quincy pressure lubed compressors: head pressure release

Or maybe any Quincy in general...

Q: When the compressor kicks off due to hitting the shut off pressure (150psi in my case), is there a noticeable pressure release sound that is supposed to occur to signify the head is depressurizing? I don't really hear anything like I do on my Craftsman, which make an audible "hiss" after shutting off.

I'm gonna be ordering some maintenance parts for mine so I wanted to see if there was something I should be looking to replace.
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Old 09-26-2007, 01:35 AM   #2
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Default Re: Quincy pressure lubed compressors: head pressure release

Check the parts list for your particular model for an item called Head Unloader. On some machines it may also be called a centrifical unloader.

The Crapsman probably employs an unloader on the pressure switch with little or no muffler on it. Totally different concept from the Quincy.
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Old 09-26-2007, 11:25 AM   #3
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Default Re: Quincy pressure lubed compressors: head pressure release

I believe I found the parts you're talking about...the question is, where do I start?


BTW, I have a hydraulic unloader (loadless starting) if that makes any difference.
Attached Images
File Type: jpg unloader.jpg (47.3 KB, 23 views)
File Type: jpg unloader2.jpg (38.9 KB, 19 views)
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Last edited by bmwpower; 09-26-2007 at 11:28 AM.
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Old 09-26-2007, 11:46 AM   #4
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Default Re: Quincy pressure lubed compressors: head pressure release

I would suggest that you don't mess with the head, unless there is a specific reason to do so. I don't hear any sounds when mine shuts off, nor do I ever hear any loss of air, however, I know that the tank will leak down overnight due to the valves in the top of the head leaking. Mine was repaired twice under warranty, and it still isn't any better now than the day that I purchased it. It still isn't any worse either after 15 years, so I call this "a draw". I watched as the service guy took mine apart, cleaned it and reassembled with new parts. It appears that it is a complicated mechanism, because the time that I called for service, they said that there was only one mechanic that did the valve servicing and I would have to wait till he had time to get to my machine. Being a homeowner, they put me at the bottom of the priority list. If it isn't broken, don't fix it....
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Old 09-26-2007, 12:06 PM   #5
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Default Re: Quincy pressure lubed compressors: head pressure release

Quote:
Originally Posted by Junkman View Post
I would suggest that you don't mess with the head, unless there is a specific reason to do so. I don't hear any sounds when mine shuts off, nor do I ever hear any loss of air, however, I know that the tank will leak down overnight due to the valves in the top of the head leaking. Mine was repaired twice under warranty, and it still isn't any better now than the day that I purchased it. It still isn't any worse either after 15 years, so I call this "a draw". I watched as the service guy took mine apart, cleaned it and reassembled with new parts. It appears that it is a complicated mechanism, because the time that I called for service, they said that there was only one mechanic that did the valve servicing and I would have to wait till he had time to get to my machine. Being a homeowner, they put me at the bottom of the priority list. If it isn't broken, don't fix it....
Sounds good. I definitely don't want to muck with something I don't have to. I just didn't want to cause any harm if it was indeed not letting the pressure out of the head - didn't want to blow any seals or anything. I can hear, what I believe to be, a slow air leak from the valve area when the compressor has shut down. After about a minute it stops. I'm guessing this is residual air leaking from the valves. Thanks!
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Old 09-26-2007, 03:44 PM   #6
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Default Re: Quincy pressure lubed compressors: head pressure release

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Originally Posted by Junkman View Post
I would suggest that you don't mess with the head, unless there is a specific reason to do so. I don't hear any sounds when mine shuts off, nor do I ever hear any loss of air, however, I know that the tank will leak down overnight due to the valves in the top of the head leaking.
There shouldn't be any pressure on the valves if the head unloads when it shuts off. The check valve at the tank inlet may be bad.
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Old 09-26-2007, 04:44 PM   #7
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Default Re: Quincy pressure lubed compressors: head pressure release

The problem may be in the control valve. The valve is located on the side of the crankcase. There should be a 1/4 line from the unloader valve on top of the head going down to the valve on the crankcase. There is a brass valve that gets moved by oil pressure when the compressor starts (thus hyd. operated) Make sure this valve is clean and free.

Oil type makes a lot of difference in this compressor.
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Old 09-26-2007, 07:23 PM   #8
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Default Re: Quincy pressure lubed compressors: head pressure release

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Originally Posted by russlaferrera View Post
The problem may be in the control valve. The valve is located on the side of the crankcase. There should be a 1/4 line from the unloader valve on top of the head going down to the valve on the crankcase. There is a brass valve that gets moved by oil pressure when the compressor starts (thus hyd. operated) Make sure this valve is clean and free.

Oil type makes a lot of difference in this compressor.
I will have some Quin-Cip oil on the way soon. Not sure what's in the compressor right now.

The pump builds oil pressure fine. Not sure how to take apart this valve to check things.
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Old 09-26-2007, 07:28 PM   #9
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Default Re: Quincy pressure lubed compressors: head pressure release

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Originally Posted by bmwpower View Post
I can hear, what I believe to be, a slow air leak from the valve area when the compressor has shut down. After about a minute it stops.
It sounds like it is fine. When the head unloads, all pressure is relieved from the top end and the piping between the compressor and the tank. The tank check valve holds the pressure in the tank.
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Old 09-27-2007, 01:38 AM   #10
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Default Re: Quincy pressure lubed compressors: head pressure release

I have a set of big Quincys at work and they do not make a big show when unloading. Good stuff.
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Old 09-27-2007, 02:43 AM   #11
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Default Re: Quincy pressure lubed compressors: head pressure release

Let it pump up to shutoff.
Pull the electrical disconnect for your safety.
Wait a couple minutes.
Grab onto the pulley/flywheel, and try turning it over in the proper direction.

If you can turn the pulley, the unloader is working.
Leave it alone. It's a Quincy they outlive the original buyers generally.

Change the oil, and forget it for a year or so.
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Old 09-27-2007, 07:02 AM   #12
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Default Re: Quincy pressure lubed compressors: head pressure release

Maybe I will take a movie of the thing. It's easier when you can hear it yourself.

I agree - leave it alone.
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Old 09-27-2007, 12:35 PM   #13
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Default Re: Quincy pressure lubed compressors: head pressure release

Won't help me a bit, I'm on dialup.
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Old 09-27-2007, 12:50 PM   #14
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Default Re: Quincy pressure lubed compressors: head pressure release

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Won't help me a bit, I'm on dialup.
Ok. 2 movies. One with video, one only audio?
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Old 10-11-2007, 07:05 PM   #15
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Default Re: Quincy pressure lubed compressors: head pressure release

Quote:
Originally Posted by russlaferrera View Post
The problem may be in the control valve. The valve is located on the side of the crankcase. There should be a 1/4 line from the unloader valve on top of the head going down to the valve on the crankcase. There is a brass valve that gets moved by oil pressure when the compressor starts (thus hyd. operated) Make sure this valve is clean and free.

Oil type makes a lot of difference in this compressor.

OK...this may be my problem. With the tank full, I removed the line from the head to the tank...no air loss. There is air coming from the unloader seals up top (8.2). To me that means air is getting past the brass valve you are talking about. No air is supposed to pass this valve when the compressor is OFF right?? It's leaking enough that I can hear it across the garage. Only air should be in that line, correct?
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Old 10-11-2007, 07:29 PM   #16
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Default Re: Quincy pressure lubed compressors: head pressure release

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Originally Posted by bmwpower View Post
OK...this may be my problem. With the tank full, I removed the line from the head to the tank...no air loss.
Good. That means the check valve is good, and your tank won't leak down when shut off.

Quote:
Originally Posted by bmwpower View Post
There is air coming from the unloader seals up top (8.2). To me that means air is getting past the brass valve you are talking about. No air is supposed to pass this valve when the compressor is OFF right?? It's leaking enough that I can hear it across the garage. Only air should be in that line, correct?
The only pressure in the top end when the unit is off is the accumulated head pressure. It should leak down (unload) quickly. Are you experiencing a continuous loss of air from the head? I'm not quite sure how that could happen (assuming a good check valve at the tank)
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Old 10-11-2007, 07:33 PM   #17
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Default Re: Quincy pressure lubed compressors: head pressure release

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The only pressure in the top end when the unit is off is the accumulated head pressure. It should leak down (unload) quickly. Are you experiencing a continuous loss of air from the head? I'm not quite sure how that could happen (assuming a good check valve at the tank)
There is a 1/4" line going from the tank pressure to a "valve" on the head, then traveling up to the top of the unloaders. I think it's the valve Russel was talking about. Remember, this pump is pressure lubed and it's got loadless starting so when the pump starts up and there is a build up of air pressure (delta I guess) and oil pressure, the pump loads. It's this system that I believe is leaking now.
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Old 10-11-2007, 07:43 PM   #18
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Default Re: Quincy pressure lubed compressors: head pressure release

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Originally Posted by bmwpower View Post
There is a 1/4" line going from the tank pressure to a "valve" on the head, then traveling up to the top of the unloaders. I think it's the valve Russel was talking about. Remember, this pump is pressure lubed and it's got loadless starting so when the pump starts up and there is a build up of air pressure (delta I guess) and oil pressure, the pump loads. It's this system that I believe is leaking now.
Ah. I thought Russel was referring to a typical centrifugal unloader (line from the end of the crankcase to the head). With these, there is no additional connection to tank pressure.

If you are losing pressure with the pump stationary, I would assume the valve that is connected to the tank is the culprit. I am not sure why there would be a tank pressure connection, but I am not familiar with Quincy "loadless" starting.
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