Air tank expiration

While filling my 5 gal portable air tank I noticed that the tank has
stamped in it "Discard after 2000" or something like that. I guess I
always knew it was there, its just that for some reason I chose to
start thinking about how long one should really last. It does have
the standard overpressure pop-off valve, which I have manually pulled
to release, but I've never intentionally tried to overpressurize the
tank to check to see if the valve works as intended. The tank has not
seen a lot of usage, and I've never known water to collect in the
bottom of it. I've also never tried to remove the valve to look at
the inside of it either.
So, how long do you keep your spare air tank around? I assume
that rust is the reason that the tanks have a discard date, is that
correct? How likely is the tank to go boom, vs show a sign of a leak
if it was to rust out?
Brad

Brad Heuver
Reply to
Brad Heuver
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I always figured it had to do with liability issues; expire the tank before it's expected to ever fail and then hope that flies in any potential court cases.
I don't blame 'em a bit, there's still some crazy lawsuit stuff going on..
Fill it up with water, pump it up to twice the pressure you use, if you want to test it..
John
Reply to
JohnM
Well, that is the first half of the test (and most important) -- the second half is they measure how much the tank expands when the water goes in under pressure -- then how much they get back when the pressure is removed. It should be the same -- if they get less, it indicates the tank has stretched (yielded). That is how scuba tanks get holes drilled in them -- they fail the hydro.
Reply to
Mike Fields
It you have access to a good manual pump, fill the tank completely with water,(no air bubbles at all!) then connect the suction side of the pump to a clear plastic tubefull of water and pump to twice rated pressure. Hold it at that for a few minutes then open a bypass valve to let the water back into the tube.Any loss of water is an indication that the tank has stretched and should be scrapped.
Reply to
Tom Miller
Remember this is just a thin walled portable air tank, the kind that sells new for $20 or less. It has a pop-off valve to prevent overpressurizing. The gauge on the tank goes red at 120 pis, and I expect that near that pressure the pop off will open and vent all the air. If you manually pull the pop off, it will not shut until the tank is quite low, 70 psi or so, as it has a lot of hysterysis. These type of tanks doe not even have water drains, so filling it with water would be quite difficult. First, the whole valve mechanism would have to be removed and replaced with something different for the test. These tanks are more like propane tanks than scuba tanks or ASME compresser tanks. I think that the liability angle is the reason for the date also. But the question remains, how many of you have one of these that is expired? Brad
Tom Miller wrote:
indicates the
Reply to
bradandlee
They test high pressure vessels at 5/3 working pressure. 6/3 might be a little high.
I would check the popoff and, either set it or install one that is 125% of working pressure, and pressurize that to see if it works. A wet test may stress the tank too much.
Just what I would do.
And, adding water to any tank is the main cause of internal corrosion, which is the main cause of tank failure. That is why the bases of high pressure tanks are their thickest points.
Steve
Reply to
SteveB
I don't know. I went and looked at mine, but it is too rusty to see the date. Other than that, it works fine....................... ;-)
Steve
Reply to
SteveB
The rust problem is due to pressurizing the tank during humid weather -- and the resulting water in the tank. I suppose the bottom of the tank could eventually burst, sending the tank into the air. My tank weighs about 25lbs. Due to its age I pressurize it only to 100psi. I wonder how high a potato gun could launch a 25lb object?
Reply to
Dave
You're right of course Brad. I guess that I missed that the price was so low. What I said though, is applicable to the more expensive industrial pressure vessels. They can be pretty pricey,especially if they're made from stainless steel.
Tom
Reply to
Tom Miller
For a laugh, take a look at this:
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Chris
Reply to
Christopher Tidy
I saw the one hour TV program on punkin chunkin. My, them boys get plum serious about it. The distances were incredible, and the centrifugal devices were downright scary. If you ever see one of those coming up on TV, please alert us. It oughta be time for the next one.
Steve
Reply to
SteveB
Call me crazy, but I discard mine after the expiration date. They're so cheap--why take chances?
Reply to
AL
Hmmm... the pumpkins are said to weigh between 8 and 10lbs and are sent 4000+ feet, although they are accellerated through a very, very long barrel using unknown air pressures.
Reply to
Dave
There are also mechanical classes, using the centrifugal method, and the ancient seige machines that hurled rocks. Can't think of that name ..... duh. Both are quite impressive, and get incredible distances. One of the centrifugal machines got out of balance on the program I saw, and like a cement truck with a dried drum of concrete, just about jumped off the ground.
Steve
Reply to
SteveB
I remember seeing this on TLC or something a while back. Some of the rigs those guys had were pretty trick. Everything from compressed air to centrifugal arms to trebaches. It was fun to watch, and very impressive to boot!
Reply to
Grady

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