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Discussion Starter #1
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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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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The Penny Pincher
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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. :pimp:
 

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oldsmobile compatible
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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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pigjamelectric said:
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. :nono:
 

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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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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. :eek: But not as much a somebody knocking over a oxy/acetylene set up onto concrete. :spank:
 

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oldred said:
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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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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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. :cool:
 

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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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Glad the Jeep is on the road
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pigjamelectric said:
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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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. :nono:
 

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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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That reads like so many I have seen in safety bulletins from years past, while fortunately it is not a common occurrence it does happen far more than most people realize. Of the one's I have read about and the two I witnessed first-hand most were related to attempting a repair which should of course NEVER, EVER be done! Both of the tank explosions I looked at were caused by rust/metal fatigue but repairs accounted for the largest number of the one's I read about. Sometimes these explosions involved injury and sometimes a fatality and I can only guess at how many close calls went unreported since unless an injury or fatality was involved it was not included in those bulletins. I remember one in particular where a large tank of about 200 gals at a sawmill blew the end out and the main portion of the tank body was found nearly 1/4 of a mile away!
 

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My dad has a 60 gallon cambell hasfeld 2 stage compressor that is probly 20+ years old and it works great. We had to change the pressure switch and magnetic starter a couple years ago but other than that it is all good. There are a few leaks in our air lines so it will bleed down overnight, but i usally forget to turn it off so it stays pressurized. If bleeding don the comressor is bad is using auto drains also bad. As far as tank explosions are concerned I have taken pop bottles both2 liter and smaller ones and drilled a hallf in hole in the cap put a valve stem in the bottle the fits snuly in the neck and the cap holds it in and presurize it as high as I can get it abuot 120 psi and poke a hole in it with a nail in the end of the stick andthe blast is like a shotgun and it ecoes in the suronding woods, the first time i did it i heldit and just poked the hole but now I stand back and whack it with the stick with a nail in it since my hand was numb after doing that. any way when i do ths the bottles can fly 20' and that is not with much pressure
 

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If that compressor is bleeding down to zero (or nearly so) every night you should find out why and stop it, probably a simple shut-off valve at the tank will do it. Having to refill a compressor tank from zero every day puts a tremendous amount of unnecessary wear on the pump because of the long run time and heat build-up, occasionally dropping the tank to near zero will not not hurt anything but it adds up fast. If this happens, for example, 250 days out of a year and takes 7 minutes to refill from empty that is about 29 hours of wasted hard run time per year not to mention the wasted power. The bigger problem though is the fact that the tank has to expand and contract through each of these cycles which will greatly shorten it's service life and as old as yours is it likely will not have a lot of time left anyway so you need to go easy on it. Most people don't realize that a tank undergoes expansion and contraction during discharge/recharge but it does, not much during the normal discharge/recharge cycle but all the way down to zero and than back up to pressure causes a lot of expansion/contraction which will eventually lead to tank failure due to metal fatigue. Obviously letting the tank drain to zero is a REALLY bad idea and you really need to address this problem as soon as possible, especially considering how old that compressor is.
 

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oldred said:
If that compressor is bleeding down to zero (or nearly so) every night you should find out why and stop it, probably a simple shut-off valve at the tank will do it.
What Red says, a valve would be a good way to stop this drain down. Another thought, if you have a few leaking hoses, these hoses probably aren't far from total failure. Blow a hose, have the compressor run continuously until someone shuts it down can't be a good thing. I shut mine down EVERY time I quit for the day. Thevalve would be good insurance for the forgetful. :D
Dan
 
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