I May Have Dodged a Bullet Here
 

About a year ago I began to hear a hissing noise coming from the bottom of my air tank. I thought it was the drain cock leaking and didn't pay much attention. But no matter how much I tightened it, the noise persisted. About 6 months ago it got noticeably worse, so I quit using the compressor pending finding time to fix it. I could see no visible problem, but the noise was coming from SOMEWHERE.
So I finally took it down a couple of months ago. There is a crack in the bottom of the tank! Due to a poor design, there is no way to drain all the water out of it. The welded-in flange that the inspection plug screws into protrudes into the tank by about 1/4 of an inch. The drain cock screws into the inspection plug, so there is 1/4 inch of water in the bottom of the tank at all times. My tank had rusted through and could have unzipped at any time. If you have one of these tanks (or any tank with a 2 inch inspection plug in the bottom) you might give it a look.

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My 60 gallon compressor tank. It's only about 10 years old.

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It has a 2" inspection plug in the bottom - not a good design.

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I poked boroscope in the tank and it showed how the weld flange protrudes into the tank, leaving a lip that water can't get over when you drain the tank.

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The inside was rusted significantly.


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You couldn't see anything wrong when there was paint on the tank, but I had to heat it to get the inspection plug out and that burnt off the paint. With the paint gone, the crack was obvious. This thing could have come unzipped at any time.


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The new tank. The drain cock flange is only 1/2 pipe. The inspection plug is on the side where it ought to be. It probably weights 40 pounds more than the old tank. It's a much more substantial piece.

Drain plug can be on the side with a pickup tube, which would drain right to the bottom. The original picture looks like a poor execution of a weldolet. They are supposed to be flush on top of the tank metal, not inserted.

Where was the tank manufactured?

And as far as not finding cracks until the paint was removed, sounds like my 914-6 oil tank!

Wow Patrick, glad it did not pop and cut you in two or something. I have seen compressed air tanks let go and do impressive things.

Mine has the drain not at the lowest point, so I have to set on of the feet on a little piece of wood and then vent it to blow out the water.

In shop, and at home, we were always taught to drain the air compressor tanks, or they could be a big bang.

I never gave much thought to that situation until I saw a news article about a couple guys getting killed when an air tank blew up. :eek::eek:

"I may have dodged a Bullet Here"


Wow, Patrick, yep a big blue one. Good catch there, whew.
Considering the condition of the rest of the tank, thay clearly have a design or construction problem.

Cheers Richard

I think I would be on the phone with PUMA customer service.

There have been several threads over on Garage Journal about this risk. Several very frightening pictures/videos from incidences of tank explosion cause by old age/rust/etc. You did dodge a bullet - actually more like a mortar.

Hmmm, think I will drain my CA tank tonight!!
Thanks for the PSA and glad you are OK.

Blame the Chinese.

man that is scary.

Is there a high probability that would have failed spectacularly if left unnoticed? I would have thought the crack would just propagate and open up more of less gradually.

that pic actually made my colon twitch!

No. A better engineer than I am is going to have to explain it in detail, but the stress is greater at the point of a crack than anywhere along the crack. The surrounding structure gives the entire structure its strength. When part of that surrounding structure is breached, the stress ( and accompanying strain) at the point is more than the material can withstand without deforming. Stick a pin in a balloon and examine the carcass. It's not a balloon with a little hole in it, it's in shreds.

https://sites.google.com/site/metropolitanforensics/cause-of-explosion-of-air-compressor-tanks

Where did you get the replacement tank? I have an old (almost 30 years) Craftsman compressor and I want to replace the tank, but I've been unable to find one that costs less than a new compressor.

Here's what I did but I am super anal about water in the system since I use it to paint.

I put a ball valve at the bottom of the tank with clear tubing so you can see what comes out. I drain the tank every other day. Have a dehumidifier in the room too. In the summer, it can suck up a gallon of water every two-threesdays which seems shocking in a second story, closed room. How all that water gets in is beyond me.

First time I drained the tank after first few months of use, at least 2 gallons of rusty water came out. After that I put the ball valve in.

Even with that protocol, you'd be surprised how much water can get into the system.

Second pic is the line that goes up from the compressor into the ceiling and down to the Rapid Air system. In the summer I can open that valve midday and get a decent spray of water.

Then the filtration system. I take the first water trap off every day and let the canister and filter dry out. Even doing that, I have to revive the desiccant once a month.

It is amazing how much water gets into a system. My compressor, 80 gallon tank, runs at least 20 times a day for short periods each time to refill the system.

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You may not want one that costs less than a new compressor. I can't imagine how weak it would be. The PUMA that rusted out sells for $549 complete with motor and compressor. I paid a little over $400 for the new ASME coded tank alone. I think I got it at Compressor World https://www.compressorworld.com/air-tanks/vertical-with-top-plate/
Depending on your situation you may be better off buying a new $549 dollar compressor every few years. We do live in a disposable economy.
Or you could get a good tank that will outlive you and probably your motor and compressor.