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Old 11-17-2006, 06:23 AM
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Compressor Air Leaks

I bought a used devilbris 5hp 30gal compressor and was wondering how long the tank should hold the air pressure when not in use. It seems like even after a week, the tank is emply and I have to restart the compressor again to use. It take like 5 mins to fill the tank.


Does this sound normal or is the compressor / tank in need of repair?

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Old 11-17-2006, 07:17 AM
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Its probably just a leaky old regulator.
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Old 11-17-2006, 08:31 AM
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Could be any number of things, do you have a shutoff at the tank? Taking a week to lose pressure in a 30 gal tank is a relatively small leak and could be in the hose, fittings, quick couplings(if used), the compressor pump or in any one or more places anywhere in the system. Trying to completely stop a leak that small in the entire system is usually a losing proposition and the best solution is to install a shutoff valve at the tank. The check valve(if it is equiped with one) that prevents backflow from the tank to the pump is a common source of leakdown and if the compressor does not have one then the air leaking past the valves in the pump will be normal. Try putting a shut off valve at the tank, you should have one there anyway, so you can shut the air off to the line when not in use. This will isolate the problem and if the leak is in the line this should fix it but if it turns out to be at the compressor then the problem could be much more difficult to solve. Try the shut off valve first and then let us know what happens.
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Old 11-20-2006, 01:56 PM
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Take a squirt bottle full of soapy water and spray your
connections. I found leaks everywhere when I started, even
at a regulator and tank connections.
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Old 11-24-2006, 06:02 PM
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Although I can't help you with your question, I want to mention that it's a good idea to drain your compressor every day anyway. This maintains your tank's integrity.

Is it on this site where pictures were posted of a station wagon that succumbed to the explosion of a corroded scuba tank in the back?

Paul
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Old 11-24-2006, 06:17 PM
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Quote:
Originally Posted by pigjamelectric
Although I can't help you with your question, I want to mention that it's a good idea to drain your compressor every day anyway. This maintains your tank's integrity.

Is it on this site where pictures were posted of a station wagon that succumbed to the explosion of a corroded scuba tank in the back?

Paul
Scuba tanks are pumped up to thousands of psi. I would would like to see what 130psi would do but I dont want to be near it.
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Old 11-24-2006, 08:36 PM
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Draining the water every day is certainly a good idea but DO NOT bleed the pressure from the tank on a frequent basis! Draining the tank of all pressure frequently will SHORTEN a tank's life due to metal fatigue from excessive expansion and contraction instead of maintaining it's integrity. A tank will expand and contract some amount during normal operation but nowhere near as much as it will during a complete discharge/recharge cycle. I am not saying someone could ruin his tank by completely discharging it on occasion and there probably will be a need to do this from time to time but if done on a daily basis then tank life will be shortened. Probably on something as small as a 30 gallon tank this problem would be minimal but there certainly would be nothing to be gained from doing it.

weird- I saw, and I have mentioned it here several times in the past, a 40 gallon tank with about 175 PSI in it rupture and totally destroy the cab of a DM800 Mack truck! This thing was mounted behind the cab and the tank failed on the side facing the rear window with the resulting explosion peeling the top off of the cab, this tank failed due to internal rust and vibration from a poor mounting fixture.
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Old 11-24-2006, 09:12 PM
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Exploding tanks have always been a lil fear of mine. Like a bomb just waiting to go off. So many people neglect to maintain there compressors and it just makes me cringe. But not as much a somebody knocking over a oxy/acetylene set up onto concrete.
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Old 11-24-2006, 10:46 PM
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Quote:
Originally Posted by oldred
Draining the water every day is certainly a good idea but DO NOT bleed the pressure from the tank on a frequent basis! Draining the tank of all pressure frequently will SHORTEN a tank's life due to metal fatigue from excessive expansion and contraction instead of maintaining it's integrity.
Thank-you Old Red for your more enlightened reply on tank drainage. That makes a lot of sense. I hate to think that my advice should lead to damage or worse someone getting hurt.

It would be interesting to know how many times the wisdom from hotrodders members has helped people go about working more safely and helped avoid harm. This is truly a great site.

Paul.
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Old 11-27-2006, 01:13 PM
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I'm USAF. Had to go repair a hangar wall that an oxygen tank went through in the mid 80s. Kid that started to move the cart without checking reportedly got a severe tongue lashing and nearly had a heart attack as he watched the tank skid across the floor between two fighters before it bounced up and went through the wall, across the parking lot, and sunk about a foot in a dirt bank. Went right through the middle of an empty parking space against the building, with a car parked to each side. Talk about lucky!! That tank traveled a bit over 100' and still had the energy to embed a foot in relatively hard packed dirt. Now if it had hit him on the way out, or the regulator that popped off had hit someone/something... I don't recall what happened to the regulator, but the lightest thing will go the furthest fastest. Throw a rifle shell in the fire (well, no, don't!!) and the bullet will likely stay in the fire. The lighter shell casing is what will launch and be dangerous!
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Old 11-27-2006, 04:51 PM
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Funny that you tell that story Farna. I was just watching a show last night called myth busters and they were testing that old (myth). They got very similar results.
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Old 11-27-2006, 06:36 PM
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Over the years I have heard many stories about those bottles and a couple of them I know are fact, most probably are. One happened to a friend of mine who was a railroad employee that dropped one off of a rail service truck and he insists they tracked that thing over 1200 feet bouncing between rails before it stopped, this fellow is a no BS kind of guy and I have no doubt what he said was true. Another was in a safety bulletin, it went through a light metal garage door, a chain link fence, took out and awning and a picnic table before winding up in a swimming pool about 150' from the garage where it started it then spun around until the pressure was finally gone. Yep those things can create some excitement!
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Old 11-27-2006, 06:52 PM
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Quote:
Originally Posted by pigjamelectric
Thank-you Old Red for your more enlightened reply on tank drainage. That makes a lot of sense. I hate to think that my advice should lead to damage or worse someone getting hurt.

It would be interesting to know how many times the wisdom from hotrodders members has helped people go about working more safely and helped avoid harm. This is truly a great site.

Paul.
Not disagreeing, but providing some "old goat" info second hand....

I have had close association with two long-time, regularly used air compressor systems. One was a body shop system and "Dan the Man" insisted that the water be drained daily, to a level that significantly decreased the pressure in the tank -- not dead empty, but it would take a few minutes in the morning to cycle up, probably 2/3 or 3/4 of the way down.

The other is a boatyard system that I am still around. The water gets drained 2 or 3 times a week and the compressor is shut off on Saturday afternoon unless customers are using it, in which case it runs all weekend and all week to the next weekend, sometimes 3 or 4 weeks in a row.

The first lasted many years til the dealer went out of business, and the second is still running. At least 25 or 30 years of life each...

The logic is sound, but practices differ I guess.
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Old 11-27-2006, 08:28 PM
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Draining water does not significantly reduce the pressure and draining a tank down to about 75 PSI or so will not be nearly as bad as zero since the tank will still be expanded. This, BTW, is not just my opinion but is fairly well known fact and for examples I can give you a good one. Since this is hardly a problem with smaller tanks it was not a problem on mining trucks that use air starters and almost completely drain their tanks several times a day, that is until on one job we decided to use 60 gallon tanks to replace the smaller ones in order to increase the starter volume(bigger tanks help a lot here since this is a one shot affair that does not rely on the compressor). After a while the tanks began to develop the cracks that are common to a tank that has reached the end of it's service life but these tanks had been total discharged and recharged many times, just as if they had been completely drained everyday. These were the common medium duty tanks found on consumer air compressors and were charged to 135 PSI. Some of the larger mining trucks use much larger tanks of 80 gallons or even bigger with no problems but these are a lot heavier than you are likely to find on a normal shop compressor. I have sold and serviced air compressors for over thirty years and I have seen many tanks crack from fatigue and vibration and the ones with leaky systems that allowed them to drain frequently had a noticeably shorter service life. I never said that you would ruin a tank in a short time and in fact it may take a while for damage to appear, probably many years on a heavy commercial unit but for the common consumer units which are quite a bit lighter the cracks can appear in a much shorter time. Drain yours if you like but it's service life will suffer.

As an added note tanks which reach the end of their service life and fail from fatigue, whether in a normal time or accelerated from excess expansion/contraction, rarely do more than just develop cracks usually around a weld at the mounting feet or pump/motor brackets and do not present much of a danger. Tanks that have reached this point must be scraped and should NEVER be repaired by welding or any other means and to attempt to repair one can be extremely dangerous.

Last edited by oldred; 11-28-2006 at 06:57 AM.
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Old 11-28-2006, 07:26 AM
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Just thinking, all this talk about tanks and service life might lead one to think that tank failure might be a major concern but in fact tank failure is rare in a normal shop situation even on old tanks. A tank's service life is determined by, damage from rust and abuse aside, the number of expansion/contraction cycles it goes through and under normal use the tank will far out last the pump so if the water is drained regularly and it is not damaged from accident or other reasons it should never be a problem. Draining a tank to zero pressure on a daily basis is abusing it and it just stands to reason that if you greatly increase the magnitude of the expansion/contraction cycles then the number of cycles will be decreased before it fails due to metal fatigue. If you abuse your tank in this manner then you very well may experience failure in a few years, maybe sooner, but if you maintain it properly then you probably will never see a tank failure even after many years. It is not uncommon to find tanks that are 20-30 years old and even older but I would strongly recommend pressure testing one this old if it is considered for use even if it is on a running compressor, just to be safe.
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