Portable air tank life span

QUOTE: Originally posted by limd21 Compressed air is nothing to gamble with. If in doubt, get a new tank.

Truer words have never been spoken. Compressed air is just energy waiting to be released and it can be released violently. I've seen air hoses bash in the sides of tool boxes when the quick-change valves fail. On the first day of my college machine shop class the instructor showed us where two holes in the concrete block wall had been patched. One was about 6" in diameter, the other was about 2 feet in diameter. The small one was from where someone had forgotten to engage the magnetic chuck on a surface mill and fired a piece of metal against the wall. The big one was where someone knocked over an oxygen tank and knocked the valve off. In WWII torpedoes were propelled by compressed air.

Admittedly these examples are at much higher pressures than we use, but presssure is nothing to mess around with.

I am behind on this post but what nobody seemed to mention was that the biggest problem with these old tanks are with rust. What with moisture in the air it causes the inside of the airtank to rust and you know it might end up. i just priced a portable tank at wa mart and its $20 so not to bad.

He he... That's why I bought my tank new (on sale, and a hefty pricing error in my favor too! ), so I don't have to worry about the state of the tank. But I haven't really used it all that much, to be truthful, but that's probably going to change this summer (parental units won't let me airbrush indoors).

I would rather mess with a cheap compressor.

I also have been using a hand carry tank and had immediately noticed it lacks a drain petcock. I have considered checking with a local hydraulic shop over the possibilty of adding to my tank.

As for the topic at hand, a 7 gallon tank at Walmart is only $17.48, even over ten years that would be less than $2.00 a year ($1.75 for those who thrive on specifics). It just is not worth messing with if the care of the tank is unknown or the condition is suspect.

QUOTE: Originally posted by VF-19 But the first and second link you've shown, limd21, shows that both tanks have been neglected. I think with proper care, airtanks will last you quite a long time..

I don't disagree at all - I have no doubt that a well cared for air tank can last (potentially many) decades. But one needs to have good confidence that neglect has *not* occurred. I myself have bought a used industrial compressor/tank combo, but I checked it by opening the inspection port (required by ASME - American Society of Mechanical Engineers for most all commercial compressors) and having a look see to check for serious rust damage.

Compressing air heats it up and concentrates moisture. That's why most of us use moisture traps, to keep our paint clear. There is still always a state of 100% humidity inside a compressor tank. At elevated pressures, the corrosion effects are accelerated. Most commercial systems have an automatic bleed down circuit that drains off standing water. All of us should do it manually - that's why the drain down valve is there at the bottom of the tank. I've seen tanks that have never been drained in years that have over 1/4 the total volume filled with liquid water - very rusty at that.

Know what your buying. Look inside the tank if it has an ASME inspection port. Check for rust. If you can't look inside, give it a good rap with a hammer - it should ring clear not "thud" and you shouldn't hear any rust flakes rattling around. Check to make sure the pressure switch works and that there is a safety blowoff valve. Compressed air is nothing to gamble with. If in doubt, get a new tank.

But the first and second link you've shown, limd21, shows that both tanks have been neglected. I think with proper care, airtanks will last you quite a long time. I picked up an oil less pump with a small tank attached to it (and a drainage plug too boot), and I figure, as long as I treat it properly, it won't explode on me. Besides, I don't really need much pressure out of it. The tank's rated for 100 psi, but I can go for a bit on 80 psi (My regulator attached to my airbrush is usually set for 15-20 psi).

If in doubt...
http://www.doli.state.mn.us/airtank.html
http://www.spe.org/pdf/airtankexplode.pdf

I agree with Quincy.

You are not going to get more than 120 psi in those tanks unless you fill them with a compressor used for scuba tanks.
I wouldn't worry too much about it.

Mike

In 30+ years in aviation, I've never seen or heard of a low pressure air tank having a catastrophic event when used within the limits it was designed for. I have two low pressure oxygen tanks (400 psi max) which came from a C-54 that was built in 1944 that are used daily (150 psi) and I don't worry about either of them. As most portable tanks are rated at 250 psi max, I would almost bet good money that somewhere, someone who had a 7 or 8 year old tank tried to fill it with high pressure (500 psi or up), it blew up and they (or their relatives) sued Sears - hence the warning placard.

The ICC (Interstate Commerce Committee) requires that high pressure tanks (500 psi and up) be pressure tested every 5 years.

I guarantee you there are tons of service stations and garages around with air tanks MANY years over the limit! As Jonas said, it's a case of risk vs. expense and it's probably not worth the risk. Having one rupture is probably not a fun thing.

Personally, for how expensive the tanks are, I don't think it's worth it to keep them around. I'm sure you could get it tested, but I'll bet the testing will be more than you paid for the tank from Wal-Mart.

It's another case of risk vs. expense. To me, the risk isn't worth the expense.

HTH,
Dan