Leaky safety valve on compressor
I just got a brand new 3 HP, 220V, 60 gallon, belt drive, oil lube compressor. The instuction manual stated to run the compressor for 1 hour with the drain valve open (i.e. not filling the tank) to seat the piston rings. Done. I then closed the drain valve and filled the tank. The pressure switch shut off ~140 psi. (says 135 in manual). However, the safety overpressure valve was slowly leaking. It’s almost like the internal spring was a little weak or something was faulty with the valve. When I manually pushed on the valve it stopped leaking. It’s rated for 150 psi. I left the compressor tank charged at 130 psi overnight, but turned the power off. This morning it was down to ~90 psi but no longer leaking.
So is the valve faulty? I understand the safety valve should blow if the tank goes above 150 psi, but anything under that it shouldn’t let out any air. Seems like a waste to fill the tank to 135 and have a leak that lets it go down to 90. Yes, I have checked my outlet connections for leaks. I’m 99% sure the leak is in the safety valve, verified by soap bubbles.
Corollary question: I understand that compressing air generates heat. But how hot is normal? After the 1 hour break-in and another 20 min to fill the tank, the tank was pretty hot to the touch. I could only hold my hand on the tank for ~5 seconds before it hurt. The motor and pump were too hot to even touch. Everything cooled off after an hour or so. I don’t want to fry my brand new comperssor. So what is the “normal” heat level for a 3 HP induction compressor motor and tank?
Replies
Woodbutcher,
The heat you describe is about what I would expect given the cycle you ran the unit through, most of the time the compressor wouldn't get that hot in normal use.
The safety valve is just a rubber disc held closed against the seat by a spring. If there was dirt caught in the the valve or the rubber was damaged you would get a leak. If you press or pull on the valve you'll run some air through it, this might clear the valve and allow it to seat properly. If it continues to leak, it is defective and should be replaced.
The pressure drop overnight was probably caused at least in part by the very hot tank cooling off so there may not be a problem with the valve. Another possible cause for an air leak is air escaping back through the compressor. If the leak is minor, I would leave alone for a week or two to see if it clears up as parts seat better.
John W.
Thanks for the replies!
Mike, fill time was probably closer to 10 minutes or under. I didn't time it, just seemed like forever!
Nikki, the unit is rated for 135 psi max pressure. http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId=1613547288&ccitem=
JohnW, thanks for the remedial physics lesson. Didn't consider the higher pressure caused by hotter air. I don't normally plan on running the compressor for 1+ hour non-stop. In fact it's rated at 80/20 duty cycle, so it's supposed to have a break. The tank was still pretty warm when I shut the power off for the night. I'll try pulling the ring a couple times and letting some air blast out the valve. It doesn't leak around the threads (tested with soapy water). However, I can see the rubber disc you refer to just start to peek out of the holes on the valve (psssssss). If I push the plunger in by hand, it stops the leaking. This should be a pretty cheap part to replace if it's defective, so no big worries just a bummer on a brand new piece of equipment. It appears to have a threaded end that I might try tightening up a bit to give the spring a bit more tension.
If this brand-new compressor is leaking, it should be covered by he warranty. The pressure will drop if the tank and air are hot and allowed to cool, but while it's being used, it's just working pressure.
"I cut this piece four times and it's still too short."
Wood Butcher,
I would agree with another poster that you are pushing the compressor hard by running at the maximum pressure, it's like red lining a car's engine, you can do it but it doesn't improve the engines life span.
I would run the unit at as low a pressure as possible that gives you the operating pressure you need for the tools you are using. With a sixty gallon tank you should still have adequate storage volume for most air consuming jobs at a lower pressure. Start out with a lower setting and only raise the cut out pressure if experience proves that you need it. If you really need to run at the maximum pressure your system is undersized.
The leakage past the safety may be caused by your getting close to the release pressure especially if the safety is set a bit light and the compressor cut off switch is cutting out a little bit higher than it is set for. None of the pressure registering components of a typical compressor are all that accurate, I would assume that any of them could be off by 10 pounds or so plus or minus.
Hope this helps, John W.
JohnW,
Thanks again for the suggestions. Most of the stuff I use compressed air for does not need to be at 135 psi. I use the blow gun more than anything, followed by the HVLP sprayer only occasionally. I'll see if I can turn down the cut-off switch down to 115 or so. I'd also like to turn the cut-on pressure down to about 80 psi. Hopefully the manual explains how to do this. This compressor is definitely overkill for my needs, but I just fried a 21 gallon HF compressor, so I wanted to buy the last compressor I'll need for 30 years.
Quoting:
"It appears to have a threaded end that I might try tightening up a bit to give the spring a bit more tension."
The adjustment you are contemplating "tightening up" is the means by which the valve manufactrurer sets the actual relief pressure. You can quickly change your 150# safety relief valve into a 200# or 250# or 300# relief valve .... more or less rendering it useless. Often one only has to unseat these valves one time, and they refuse to seal back. Poor quality. I'd approach your dealer for a new one under warranty, or simply buy a new, higher quality one and be done with it.
John in Texas
For starters, it should not take 20 minutes to fill 60 gallon tank.The tank should not get hot, warm maybe.As far as the safety valve leaking, a new one should not leak that much air overnight.Many compressors will leak a small amount of air over a days time, not a problem . Your compressor is leaking too much air and the fill time is way excessive.I would guess that 5 or 6 minutes to fill 60 gallons would be more like it,except for the first time from dead empty. Then maybe 8 minutes.
mike
JohnW knows what he's talking about. But I would also check all the threaded fittings to see if any are leaking. A little soapy water brushed on each will tell the tale.
Isn't setting the pressure regulator at 130 lbs on the high side? Have you tried setting it at about 120 lbs. to see if that makes a difference?
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"I would never die for my beliefs because I might be wrong."
-- Bertrand Russell
NEW.. I would call the company and get a new valve from them.. Could be just a bad seat.. However I would think they test the tank with the valve shipped. Well, at least they should..
Anyway.. I think you got a legit gripe!
Just checking: you put oil in the compressor sump, correct?
Induction motored air compressors should not cycle more than 12 times an hour and 6 is preferred. If it does you need a larger compressor or at least a secondary tank. Aloha, Mike
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