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Compressor leaks down..... grrrr

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cathead

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#1
My compressor leaks down over several days. If I'm not actively using it I shut off the breaker but it is a big energy waster.
I have checked all the fittings with soapy water and can't find any leaks. The pressure is escaping somewhere. Is there
a valve where the pressureized air enters the tank that leaks back into the compressor head maybe? It's a Sanborn 5hp 220V 80 gallon
compressor, about 15 years old. This condition seems to gradually occured over the last year or so.
 

thomas s

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#2
I think it could be the unloader valve. It releases pressure from the head so the motor does not start under load. look for the tube going from the head to the tank.
 

mksj

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#3
You have a compressor check valve that goes into the tank, the valve actually sits in the tank and then connects to the HP pump side outlet. The valves get crud/rust in them or just stick and do not seal. Most of these come with a small side port which goes to an unloader which bleeds air off the HP pump side until it comes to speed. I just replaced this valve in my compressor which was less than a year old. They used some iron pipe on the HP side which rusted and fowled the valve. Replaced it with brass.

https://www.jackssmallengines.com/equipment/list/air-compressor/Check-Valves/254:Sanborn
 

cathead

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#5
You have a compressor check valve that goes into the tank, the valve actually sits in the tank and then connects to the HP pump side outlet. The valves get crud/rust in them or just stick and do not seal. Most of these come with a small side port which goes to an unloader which bleeds air off the HP pump side until it comes to speed. I just replaced this valve in my compressor which was less than a year old. They used some iron pipe on the HP side which rusted and fowled the valve. Replaced it with brass.

https://www.jackssmallengines.com/equipment/list/air-compressor/Check-Valves/254:Sanborn
That sounds about right. I will be ripping into it soon. Thanks!
 

RJSakowski

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#6
I have had problems with the in-line check valve. The unloader valve will not provide enough flow to create enough pressure drop to properly seat the check valve. In my case, there is a very distinct hiss of escaping air but I could see a minor leak being unnoticeable. You should see a leak with a soap bubble test. If it continues for more than a few seconds, the check valve is faulty.
 
Last edited:

coffmajt

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#7
another place to check is the unloader valve diaphragm, Some of these have several small screws that over time can let air slowly leak from under the diaphragm. Good hunting.

Jack
 

Nogoingback

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#8
My compressor also has a drain valve in the bottom of the tank. If I'm not careful in closing it (it's hard to reach), it can leak slowly as well.
 

fixit

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#9
If it take 2 to 3 days to leak down I would not waste my time or money to mess with it at this time. When you can see the PSI drop between cycles it's different, you have a problem. Just my opinion.

fixit
 

RJSakowski

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#10
My compressor is a 30 gallon Sanborn. Other possible leak sources would be the pressure switch diaphragm or the manual pressure release. A pinhole in the diaphragm or a bad gasket would be hard to spot. Other possibilities are the main pressure gauge or the pressure regulator. Again, internal leaks would be hard to spot.

An 80 gallon tank holds about 10 cu. ft. or some 100 cu.ft. of uncompressed air. A leak down time of 50 hrs. would be around 2 cu. ft./hr. which is a fairly substantial leak. I would use a mechanic's stethoscope to try to locate the leak. Not having a stethoscope, a length of flexible tubing will work.
 

cathead

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#11
My compressor is a 30 gallon Sanborn. Other possible leak sources would be the pressure switch diaphragm or the manual pressure release. A pinhole in the diaphragm or a bad gasket would be hard to spot. Other possibilities are the main pressure gauge or the pressure regulator. Again, internal leaks would be hard to spot.

An 80 gallon tank holds about 10 cu. ft. or some 100 cu.ft. of uncompressed air. A leak down time of 50 hrs. would be around 2 cu. ft./hr. which is a fairly substantial leak. I would use a mechanic's stethoscope to try to locate the leak. Not having a stethoscope, a length of flexible tubing will work.

This morning I leak tested the output line by putting an MT 3 taper dead center over the hole and spraying it with soapy water, no leaking there.
Also, I disassembled the overpressure spillover for inspection and cleaning, all seemed OK there. Also, I took Jack's
recommendation and tightened the 6 Phillips on the bottom of the pressure switch assembly. It's up to pressure now at
165 pounds so will go out to the shop again and listen with some flexible tubing. Time will tell if it's leaking as it has been cycling about twice a day
with no usage...
 

cathead

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#12
There is a main valve that I shut off to prevent my overhead lines from leaking down as there are many threaded connections and probably
50 or so feet of pipe. With the main shut off, I could detect a tiny bit of air coming from an air nozzle by feeling the cool on my tongue. :p The leak was
not detectable by ear at all. Apparently I need to replace the seal on the main outlet valve. I also noticed that if I tightened up the valve very tight,
the leak was all but undetectable. I will check my gauge in the morning but I am pretty sure the valve is at fault. Sometimes it takes the
"process of elimination" to get to the root of the problem.

What is the most secure valve to use that will not leak? My thoughts would be a water line type valve sealing with rubber or possibly
a ball valve, certainly not a gate valve.
 
Last edited:

Groundhog

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#13
I have had better luck finding air leaks using a piece of hose or large diameter tubing held to my ear and probing likely areas than by using soapy water. And I am about deaf. (it helps if the area around you is quiet).
 

Nogoingback

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#14
What is the most secure valve to use that will not leak? My thoughts would be a water line type valve sealing with rubber or possibly
a ball valve, certainly not a gate valve.
Where I live there's a business that specializes in compressor sales and service. If you have someone near you like that, you could just call and
ask what they use.
 

RJSakowski

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#16
A ball valve with stainless steel ball will have the least flow resistance and is least likely to have problems with debris. The former occupant of a building we once rented used ball valves for all of their test gas lines.
 

SSage

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#17
I've had a few ball valves leak in my system I used for isolation, I just pulled 3 out of the lines. I now run a single ball valve at the tank and took out the unneeded quick connects I had everywhere.

My leak was mainly from the older air/water separator I got off eBay. Sometimes it would seal up, but many times it would leak air out the auto drain. I went with a new 3/4" RapidAir regulator/filter set up since I use a 3/4" Maxline system. Its leak free and holding back the 165 psi just fine so far. Its actually working good, air is much drier than the old unit.

I also had a problem with the unloader valve, replaced mine recently. My Ingersol Rand 80 gallon has the valve built into the electrical switch. $80 replacement. I can't complain though, my IR compressor from Tractor Supply was only $899 and its over 4 years old. I run it almost everyday fairly heavy. Surprised its held up so well. Highly recommend the RapidAir Maxline system, haven't had a leaky fitting yet.
 

terrywerm

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#18
Another vote for a ball valve with stainless ball. They work very well.

When I took care of compressed air systems for a previous employer, they allowed me to purchase an ultrasonic leak detector. It was very expensive, but the energy savings that were realized from having a leak free system paid for the tester in no time. It also came in handy for diagnosing leaky or troublesome steam traps in the production heating systems. It was capable of finding nearly imperceptible air leaks from better than 20' away. I could also scan the entire plant air system for leaks on a monthly basis in just over an hour.
 
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