I've got a Curtis air compressor that has been in the family for the last 30 years (its one year older than me according to the tag that has been tacked onto the tank) . Its been reliable and faithful and I'm now in the process of cleaning and repainting while my new shop is being built.

Its never given me a bit of trouble and has worked reliably since Dear old Dad bought it 2nd hand back in the 70s. Its a horizontal tank with a drain petcock that is mid height in the tank and has always been a pain to drain the water out. I try to keep it drained but where the petcock is I could never be sure that it drains fully.

With a 43 year old tank, should I be concerned about running up to 150 PSI given its age or am I worrying too much?

While uncommon it does happen that an air compressor tank will suddenly burst and send shrapenel everywhere. Ususally what happens is that you get pinholes in the tank from rust those are a clear sign that your tank should be retired.

My question is why do you need 150psi? Most 2 stages go that high but there is no need for you to run it that high pressure. Turn the pump down to 120psi

I've never adjusted the PSI from where it was when it was in Dad's shop. He ran it that way for as long as I could remember. I have thought about replacing the tank, and possibly mount the new one vertical so that I could save space and ensure that it can drain fully.

In my new shop I'll have stairs leading up to a loft and thought about enclosing the space under the stairs and putting the compressor in it to help keep the sound down.


While uncommon it does happen that an air compressor tank will suddenly burst and send shrapenel everywhere. Ususally what happens is that you get pinholes in the tank from rust those are a clear sign that your tank should be retired.

My question is why do you need 150psi? Most 2 stages go that high but there is no need for you to run it that high pressure. Turn the pump down to 120psi

If you are concerned, you can check with your local welding supply house about the possibility of having them pressure test the tank.

Most of the compressor tank problems that I have seen are like Goat mentions -- pinhole leaks from rust that grow to the point that you cannot keep air in the thing. A contractor I know did show me a pancake tank he had that ruptured, though. Never did know exactly why it went.

I've thought a couple times about the possibility of using one of those gas tank sealers on the inside of my air tank to prevent the rust issue. Talked to the rep from POR-15 and he figured that it would work, just that the main issue would be rolling the 80 gallon tank around to get it distributed... :)

you could sandblast the tank. it will serve to purpuses 1) to clean it and ready it for paint. 2) if its starting to rust thur you will see the badly rust areas and/or break thur them. also put the petcock where you can get to it.

I have a big Curtis compressor from 1968, and I've also been restoring it. I got it for a song. Some ideas that have been thrown around are:
1. Fill 1/4 full with gravel, mount on a rotating spit to clean rust out. Run it 24 hours or something.
2. A gallon of POR15. I talked to the POR engineer, he said this should work.
3. Automatic drain. HF or Mcmaster/Grainger.

The tanks on old Curtis comps are very thick. You probably won't have any trouble.

I have a big Curtis compressor from 1968, and I've also been restoring it. I got it for a song. Some ideas that have been thrown around are:
1. Fill 1/4 full with gravel, mount on a rotating spit to clean rust out. Run it 24 hours or something.
2. A gallon of POR15. I talked to the POR engineer, he said this should work.
3. Automatic drain. HF or Mcmaster/Grainger.

The tanks on old Curtis comps are very thick. You probably won't have any trouble.

That is good to know about tank thickness.

After all this time I have no idea of tank capacity.. its about 20" in diameter and 5 feet long. It has 2 portals w/caps on the side about 3 inches in diameter that a pipe wrench would fit and the caps have never been off. I guess during the restoration process I could get one off and actually look inside.

Anyone have a clue as to how big the tank might be?

The shop won't be finished till probably Aug 1 so I've got time to get it inspected, cleaned up on the outside and possibly , just have to figure out a way to do it in my new garage without making a gigantic mess. Ive got it so full of stuff to go into the shop (I left a nice 30x30 space at the old house and have a 26x35 3 car attached garage that I've got packed until the new shop is built, a 30x40).

My curtis was made in 1955 and is still going strong. We use it most everyday so I bet you still have a few good years left in it.

If your worried about noise enclose it for soundproofing and sheath it in something that will absorb any shrapnal if your really worried about it. I have seen lots of compressers develop pinholes, had them welded and they are still going. I have heard the urban rumors about tanks ripping apart, but never 1st hand. In the world of pressure 150psi is not all that great, and I just don't think its possible that a tank would rip apart and that metal would actually go flying. Maybe, and its a big MAYBE, for the sake of argument it would rip open, but ripping apart into shrapnal is a long stretch from there.

Air compressors and hot water tanks are very different animals, but not too different. Here's one example of the stored energy:

My buddy just got back from Iraq where one of his jobs was explosion investigation. One of the tanks in their hooch blew up (no pressure relief valve) and everybody thought it was a single incoming mortar round until they found the tank on the other side of the wire. Left a crater and everything.

I'd probably just make sure I replace the pop-off when you repaint. And watch out for the pin holes. We had one growing up as a kid with a few pin holes. My Dad just kept putting bigger sheet metal screws in - not sure that was a good idea!

On the positive, my father in law runs his Daddy's compressor too. Joe is almost 60 and his Dad is over 80. All three of them are still going strong... Good luck.

your meaurements indicate an 80gallon tank

Why not pull off the inspection plugs and look inside? Go from there. That's what the government makes us do for out annual inspections of their tanks.

Why not pull off the inspection plugs and look inside? Go from there. That's what the government makes us do for out annual inspections of their tanks.

The mechanicals are in good shape but the outside of the tank is in dire need of a paint job so pulling the inspection plugs and finding out the status of the inside is probably the next step. This has been a very informative thread.

I agree w enclosing it. You'll eliminate any concerns about shrapnel and maybe gain a little light duty work/storage space, ie if it's a horizontal tank build a little box around it and you can set things on top..........you can never have enough horizontal surfaces in a shop! Otherwise the compressor is just sitting there eating up floor space.

Even better, move it to a "Tuff Shed" next to the shop. This is what I did, it's awesome.

What about drilling a hole in the bottom and welding in a new petcock? That way you can drain the entire tank.

My calculations have you at about 80 gallons.

Unless you are enclosing it with 1/4" steel plate welded and reinforced, don't bother. The amount of energy stored in compressed air is staggering. I've heard of compressors that blow taking out walls and building corners. MOST likely, when it begins to go, it will be pinholes not unzipping. You'll get plenty of warning. Unzipping is very very rare.

Cleaning the inside of the tank may be an exercise in futility. I got a 80 gallon vertical tank that was in a toyota dealership for probably 20 years until the compressor finally destroyed itself.

It probably had a quart or so of liquid 'gunk' in it that I drained. Finally cut the tank apart later and found that the whole inside was coated in at least 1/4" of rust and greasy gunk. There was probably a good 1/2" of greasy crud and rusty metal flakes in the bottom of it too. It would be a real challenge to clean the inside of one like that so it could accept paint. The oil vapor from the compressor had taken its toll over the years.

HOWEVER, the tank was actually in great shape, minor pitting in the two domes. None in the walls. My guess it it would have lasted for many, many more years if I had used it as an air tank without any problems.

Good luck trying to get the plugs out. I couldn't get mine out.

I've cleaned my '68 Curtis 120 Gallon tank, and it had no oily gunk in it, just dry rust flakes. I think unless the compressor destroyed itself once, you won't find any oil. The tank on mine says endcaps are 0.28" thick, and the shell is 0.2" or something like that. That's pretty strong for an air receiver, I'm sure yours is similar.

My compressor is still fairly new -- just a few years old. So I figure that if I'm going to do something about cleaning and sealing the inside, I should do it soon before there is a chance of the gunk building up. So far, what comes out of the drain petcock is just rusty colored water without any oily residue so I could probably get away with the gas tank etch and sealer route.

My compressor is still fairly new -- just a few years old. So I figure that if I'm going to do something about cleaning and sealing the inside, I should do it soon before there is a chance of the gunk building up. So far, what comes out of the drain petcock is just rusty colored water without any oily residue so I could probably get away with the gas tank etch and sealer route.

All this information is very good to know. I'll see what is in there when I break it down next weekend and start to clean it. I think that the inside should be fairly good and see what I can do to seal the inside and what my options are for putting a better drain in it. I don't want to go welding on the tank if I can help it but there has to be a better way to drain it than the petcock in the middle of the endcap.

I've heard of filling tanks with water and then pressurizing them to 300psi to check them, my girlfriend's dad was telling me about doing that on the job (pipe fitter/johnson controls) to test tanks that they make, water just squirts out instead of the tank exploding. Not sure it's it's a good idea or not, just head of it.

Pressure tests are usually done with the vessel filled with liquid. Gases compress, so there is a lot of stored energy in something like compressed air. Liquids don't compress to any real degree, so there is no stored energy when the vessel fails. Taking it up to 300 psi would definitely "test" the tank, but I have no idea if that is really more than you would need to use. You would not want to put undue stress on the tank. You'd have to determine a realistic safety factor. Two times the working pressure? Two and a half?

You guys are so overthinking this whole thing. Aside from urban rumors who has actually witnessed a compresser tank that has come apart? Let the sleeping dogs lie. What if you fill the dam thing with water and it starts leaking at 250 psi?? Now you have taken a tank that might have lasted 20 more years and fawked it up. So theres oil, gunk, or rust flakes in your tank, is it getting into your airlines and fawking up your tools? You should have a filter which will catch that shit. Drain your tanks regularly, and leave them the fawk alone. If you don't have a drain then drill a hole and weld in a threaded insert and install a ball valve. Don't do it in the lowest point of the tank, that will be the weakest place if you do have corrosion. Drill your new drain hole at one of the ends where you are sure the tank is plenty sound, and just tilt the tank to make that the new lowest point.

There is enough stored energy in a compressed air tank to give it a healthy respect. Like a stick of dynamite or two. The original poster has valid concerns. Don't be a Darwin award winner.

There is enough stored energy in a compressed air tank to give it a healthy respect. Like a stick of dynamite or two. The original poster has valid concerns. Don't be a Darwin award winner.


Show pics of a tank that exploded with normal pressure that caused damage, or tell of your 1st hand knowlege. Otherwise your just passing on more smack :rolleyes:

http://www.doli.state.mn.us/roch_air_cmprsr_fail.jpg

http://www.doli.state.mn.us/roch_air_cmprsr_fail2.jpg

Who the fuck cares about damage...I'd more worried about being in the same room when the thing goes...even if there is no shrapenel, can we say ruptured ear drums :eek:

There is enough stored energy in a compressed air tank to give it a healthy respect. Like a stick of dynamite or two. The original poster has valid concerns. Don't be a Darwin award winner.


I think that given the age of the tank, 43 years old I would want to know of the potential hazards should it fail and if I have reason to be concerned. Many of the posts say, yes.

With that I believe that I will spend the $$ to have it pressure tested properly to know if it is questionable and if it passes and is deemed OK then I'll work toward sealing the inside and reset the pressure to 120PSI down from 150PSI that it is originally set.

When it gets right down to it, I'd rather not know what would happen shoudl it fail.

As I said in an earlier post, I did see a pancake compressor tank that had ruptured. I agree that the most common failure is pinholes due to rust. But as mentioned, compressed air does have a lot of potential energy and I would err on the side of caution if I had any misgivings.

Show pics of a tank that exploded with normal pressure that caused damage, or tell of your 1st hand knowlege. Otherwise your just passing on more smack :rolleyes:


Using the Dan Crowl formula a 60 gallon tank @ 150psig has the stored energy equivalent to approx. 1/3 pound of TNT.

I have heard a 120 gallon receiver tank go off during startup; it left dents in ¼” checker plate and ripped the handrail off the platform where it was mounted.


It is easy enough to hydro test your tank yourself with a pressure washer, 2 gauges and a few suitable valves. Take it up to 200psig and let it sit for an hour, if you do not lose any pressure or observe any leaks you should be good for another few years. Another option would be a manual hydrostatic test pump that you should be able to rent for $15/day at a tool rental.

http://www.pollardwater.com/emarket/Images/Model29100.gif

About the tanks un zipping. A mechanic that I work with has a nasty leg scar from a cheapo air compresser blowing up. I don't remember the details of the compressor. It was along side the car in the garage. It was a hand-me-down from someone in his family and he couldn't get any $$$ from the air company.

He now has a cage around the inside of one of those plastic yard cabinets and it setting outside the garage now.

BTW, I got a free running 60-80 gallon air compressor that is from Champion Pnewmatic(spelling?). It's got a riveted tank and need a pump rebuild bad. I quit using it because of that mechanics story. I'll buy a real one this summer. But for now it's collecting dust. Would a comp from the 1940's(guesstimate from a air comp jobber) be worth anything?

I've seen what an air tank can do if they rupture. It isn't pretty. It took out the garage roof and the adjoining neighbor's block garage wall. Fortunately no one was in the immediate area when it blew.

I also witnessed a time when an air valve was knocked off of an oxygen bottle for a torch set at a local high school shop. That bottle went through 6 block walls and landed out on the football field.

I'd at least pull the plugs on the tank and do a visual inspection. If there are any pits from rusting (compressors are notorious for collecting water!) I'd not use the tank.

i'm a mechanic for a garbage company i find old compressor tanks cut the bottoms off and use them for fire pits works really good but most of the ones i cut are pretty old most from the 70's and all of them were really clean just some surface rust