Stupid question. Water PSI vs. Air PSI.

[pickardracing]

So I got this quite sizeable welded metal tank from my old work.

It was the air/hydraulic tank for the in-ground lifts. It says on the tank that it is rated at 'W.P. 200' which i am assuming means 200 PSI of water pressure. I'd like to use this tank for my air compressor, so I need to ask a few questions.

Is there a difference in the PSI ratings for water vs. air? If so, assuming this thing can hold 200 PSI of water, how much air pressure can it handle?

[DoubleAron]

I bet it means working pressure. That would be the pressure it is at most of the time while it is working, not including any spikes the system might see.

[PonyKiller87]

Yeah, that should be fine for a air compressor. Hydrolic stuff usualy works at much higher preasures than what your air compressor is going to do. If your worried about it at all. Use a air hose and air it up in the back yard a few times to make sure it holds.

[Windsors 03 Cobra]

Yea thats working pressure, I would be careful letting a smaller-ish compressor running for 30 minutes to fill up a ginormous tank which could cause undue stress and damage on the compressor head.

[pickardracing]

I wouldnt say that it's ginormous, in fact it's probably smaller than the big compressors they sell at lowes.

It's about 5 feet tall and 18-20 inches in diameter. About double the size of my current 20-ish Gallon tank.

I'm going to have to weld on the mounting plate for the compressor and motor, plus do a little working to get the lines and whatnot right, but all in all, it was a good pick-up if i can make it work.

[Russ Jerome]

It's about 5 feet tall and 18-20 inches in diameter. About double the size of my current 20-ish Gallon tank.



Without pulling out the calculator that would be about triple
your 20 gallon tank. 200WP is a kick butt tank for a compressor
if your comp CFM and duty is up for the work. I would plumb
it and upgrade the head unit down the road if need be, good size
for painting at home.

[Al]

If it says 200' ... the ' stands for feet. In water, 15 feet equals 1 barr equals 15 psi. I guess that a foot of water equals 1 psi?

[Reverend Cooper]

is it me or is al way to fvckin smart for us

[Silver03SRT]

didnt you pay attention in school??? ^^^^ lol jk now that i hear those words its all coming back to me

[Russ Jerome]

is it me or is al way to fvckin smart for us

14.7 technicaly :)

Water weighs 8.3# per gal, "WP" is a measure of pressure not distance :)

[Reverend Cooper]

^ i love Russ

[SSDude]

If it says 200' ... the ' stands for feet. In water, 15 feet equals 1 barr equals 15 psi. I guess that a foot of water equals 1 psi?

A cubic foot of water weighs 62.4 lb. and exerts .4333 lbs of pressure per square inch on the bottom of its container at a depth of one foot so 15 feet equals approximately 6.5psi
Technically you should be certified to weld on a pressure vessel but hey just don't burn through. I'm betting you will be wishing for a bigger compressor head.

[Dave Bandt]

Actually, you should NEVER weld on a pressure vessel. The cooling rate must be controlled or residual stresses will remain in the weld. And if not done stress relieved, the cyclic nature of filling and emptying the tank will cause the metal to fail. Many people have died from this. You not only need to know welding but metallurgy as well, as the metal temperature and the rate the weld cools determines the grain structure of the steel. I guess i paid attention in my metallurgy class in college, huh?

[pickardracing]

Well what if it's just a matter of tacking on some brackets with a 110 wire welder?

I cant really see any damage coming from something like that.

This thing is pretty thick, I would have my doubts about it even getting warm inside.

That said, glad to see you here, Dave. How are you doing lately?

[Dave Bandt]

Well what if it's just a matter of tacking on some brackets with a 110 wire welder?

I cant really see any damage coming from something like that.

This thing is pretty thick, I would have my doubts about it even getting warm inside.

That said, glad to see you here, Dave. How are you doing lately?

People have died over "just tacking a piece of metal" on an air tank, or more correctly, pressure vessel.

The damage results in areas not visible to the naked eye. When steel alloys cool, the resulting grain structure is a function of the heat and the rate it's cooled. That's why some instances require preheating to a specified temperature and then cooling at a controlled rate. I dealt with this first hand when i worked in the mines, but i make no claim to be a metallurgist or weld expert. If you "tack" anything to the cylinder you run the risk of altering the metal composition.....more than likely causing it to become more brittle...and introducing internal stresses. The faster steel cools the more brittle it becomes. And regardless of how good you can weld, there will always be a seam on the edge of the weld where it starts, stops, and penetrates the cylinder, which causes stress concentration points. It is the cylclic nature of the filling and draining of the tank with air pressure that causes crack propogation from the regions i mentioned above. Personally, i wouldn't chance it. But i have a deep respect for safety ingrained in me from working in plants with large equipment that can easily kill you. I've seen pictures of exploded pressure vessels due to improper welding.....and i know it's nothing to mess with.

Here is a link you might want to read. Pay close attention to the Failure Factors discussion on page 2 where it makes reference to "improper repair of leak or other defects involving welding." You can basically interpret that as "any welding done when you don't know the proper proceedure." And without knowing the metallurgical composition of your tank, you can bet you won't be able to do it correctly. The policy at all places i have worked has been ABSOLUTELY NO WELDING ON PRESSURE VESSELS....due to the liability. We always paid an expert company to come in and do it if it had to be done.

http://yosemite.epa.gov/oswer/Ceppoweb.nsf/vwResourcesByFilename/rupt-ves.pdf/$File/rupt-ves.pdf

Anyway, i hope this helps. I personally wouldn't do it because you just never know if/when it would fail and who might be near if it does.

I am doing fine, thanks for asking. I recently hit a bump in the road, but my docs have a plan to deal with it.

Wishing you the best.

Dave

[pickardracing]

So maybe the best course of action would be to conjure a way to plumb the compressor head to the tank and mount it on an unattached stand next to the tank. Or find a way to plumb the two tanks together and keep the existing setup intact?

Thanks for the heads up Dave. You da man!