Air Compressor -- When to Retire - Woodworking Talk - Woodworkers Forum
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post #1 of 13 Old 06-04-2020, 09:23 AM Thread Starter
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Air Compressor -- When to Retire

I own a 17yo Craftsman air compressor (model: 919167240). It operates perfectly. I use the thing often.

Air Compressor -- When to Retire-919.167240picture.jpg

Owners of this compressor are supposed to drain accumulated water from the tank after each use to prevent internal rust. Rust potentially weakens the tank walls and that creates the very real risk of explosive decompression.

Admittedly, I drain the tank only intermittently, and only when the schloshing of water within the tank reminds me that this minor maintenance item is overdue. I realize this is a bad policy in light of the previous paragraph. I also have never used an air dryer with the thing. I am a bad owner.

So now I'm pondering the following...
Given the age of this compressor, given the less-than-idea maintenance by yours truly, and given the consequences should those two facts conspire, is it prudent to replace the thing?

I've since bought an air dryer (after 17yrs without). I'm curious if an air compressor specific rust inhibitor commercial product exists explicitly for this issue.

Comments?
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post #2 of 13 Old 06-04-2020, 10:17 AM
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What causes rust?

Water alone will not cause rust. Rust needs air/oxygen as well. If you use the compressor mostly outside it will take in more humid air than in a "conditioned" shop. Is it too late for this one? I doubt it because if the internal rust is so bad it will gradually create a leak or blow out hole on the bottom. This shouldn't be really be harmful and the hissing sound will give you enough warning to shut it down.

You could use a small tack hammer and gently tap on the bottom, listening for any change in the sound due to a thinner section of the tank. It should all sound the same, but do drain the tank first under moderate pressure. The pressure will aid in blasting as much water out as possible as opposed to just letting gravity drain it.

A piston type compressor will introduce some oil in the air stream from wear on the cylinder walls over a long period of time. This small amount of oil will help to deter internal rusting. I would continue to use it, but drain it after each use until the air pressure is zero psi.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #3 of 13 Old 06-04-2020, 01:03 PM
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Just to be certain .......

I found this video showing the rust accumulation at the bottom of the tank:


This one actually exploded, however I don't think it was because it was rusted out at the bottom. It appears that it was over pressured and the and as a result both ends blew off and the tank separated. There's no way to determine what the cause was from this video:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 06-04-2020 at 01:13 PM.
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post #4 of 13 Old 06-04-2020, 09:54 PM
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if 17 yrs of listening to an oilless compressor didn't sway you away, i say keep it until it dies
oilless compressors are not know for durability, so i'll go out on a limb and say you've never abused it
the air dryer only protects things beyond the air dryer, like your tools and piping
if you do buy another compressor, do your ears a favor and go with a belt drive, even then put it another room
a 5hp belt drive puts out less noise than a 1/2hp oilless
i can hear the contractors oilless compressors building homes half a mile from here


one in a million compressor tanks blows
some of them have hd video cameras pointed at them
all of those videos end up on youtube
jk, but you get my drift

love the tags you put on this thread

Last edited by _Ogre; 06-04-2020 at 09:59 PM.
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post #5 of 13 Old 06-05-2020, 08:34 AM Thread Starter
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"If 17 yrs of listening to an oil-less compressor didn't sway you away..."

The planer is melodious. The table saw and compound miter, a harmonious pair. The leaf blower and shopvac, sweet-sounding. The router table with a raised panel shaper purrs. Among the violently noisy tools in my garage, that screaming Craftsman compressor is the least pleasant.

Thanks for the chuckle.
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post #6 of 13 Old 06-05-2020, 09:36 AM
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You could take it to an inspection subcontractor and have themcheck the wall thickness ultrasonically. They may need to remove paint. Take readings ar 12 3 6 9 oclock and take these 4 stations at several locations lengthwise.


You will be comparing them against each other.

Retired engineer-bureaucrat in Oakland, CA. Been working with wood since the 1960's.
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post #7 of 13 Old 06-05-2020, 11:08 AM
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You could have the tank pressure tested but that will cost about $75. Call around to local fire extinguisher companies to find a tester, lots of pressure vessels need to be re-certified every ten years, I just had one of my welding cylinders done but it pressurizes to over 2000 lbs and you're only pressurizing to 120.

The test is basically as follows, they seal your vessel except for a single opening and attach a line to that opening, then they put your entire tank inside a bigger one that is full of water. Then they pump water into yours through the line and they pressurize it to multiples of it's rated pressure. The water in the larger container is connected to a sight glass, if your tank so much as bulges a little the outer water will cause the sight glass reading to rise, they can see very small movements. If they can pressurize your tank to a pressure much higher than the rating and the outer water jacket doesn't change then you pass, if the wall of your tank is compromised then it will move and flex under pressure and they will see it in the sight glass and your tank fails.

I can't see 120PSI casing a tank to explode. If it rusts through I think it would start with a pinhole that will hiss, the likely location will be right next to a seam weld.

Jeff
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post #8 of 13 Old 06-05-2020, 12:37 PM
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come on guys, let's get real
it probably exceed the value of a new compressor to disassemble and test the old tank as it is a non-conforming test
either buy a new one or put up with the old one
Quote:
shopvac, sweet-sounding
with that comment, i suspect the compressor is safe from the scrap pile
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post #9 of 13 Old 06-05-2020, 12:53 PM
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I have a few thoughts:

First, a rust-related blowout is likely to be a point leak, first - it might be startling and disruptive, but most likely (not <I>certainly</I>) not explosive. I'd be a lot more concerned about an over-pressure rupture, which will be explosive. I recently noticed that my 6-gal, 150 psi pancake compressor was still running at about 180 psi - long after the cutoff should have stopped it, and after the overpressure valve should have released. Both were not functioning. Replacing the overpressure valve is cheaper than replacing me.

Second, you absolutely should empty it to zero psi every time you use it. If the valve is sticky, sharp, or awkward, jury rig something that you can use without cutting your fingers, something you can get leverage on, or make sure you use just a hint of anti-seize compound on the threads so it doesn't rust shut but still seals. (That pancake compressor, a Porter-Cable, is a finger-slicer. :( ) Make sure the valve is down so it drains, I know you know that, but I had to show my kid once - he had to tip the compressor to get a good grip on the poorly-designed valve and he didn't tip it back!

Third, you've had a good life with that compressor, and (as my grandpa used to say) "it don't owe you a dime." If it really concerns you, you can get into a new comparable model for right around $200 on the low end, all the way up to $450 or so on the DeWalt end. I have a 30-gal/175 psi Husky vertical that's performed very well, and its 20-gal/200 psi little brother is going for just over $200 at your local Home Despot. Small price to pay to get rid of that nervous feeling every time you turn your back on the compressor.

They aren't meant to last forever - at a certain point, we put them out to pasture, I guess, and get new ones. And I hope it goes without saying, that's something I would never buy used.
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post #10 of 13 Old 06-05-2020, 01:57 PM
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Sflorman makes a good point on the drain valve. I bought a few pipe nipples and elbows when I got my compressor and "moved" the butterfly drain valve from the awkward place under the tank to a convenient place where a container easily fits under it. If you have money lying around that you don't know what to do with you can buy compressor drain valves that will leak down the tank overnight and when the pressure gets low enough it opens and releases the water. You have to remember to shut off your compressor at the end of the day or they won't work.
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post #11 of 13 Old 06-05-2020, 02:41 PM
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I have a 36 year old Craftsman 30 gallon tank compressor that is still good. Never had any problems, drained the tank when I thought about it. I leave it in the garage now because I have a 60gallon Devilbliss compressor in the shop as of two years ago.
If the tank gets a pinhole, replace the compressor. New tanks cost almost as much as a compressor. A friend of mine has a Quincy 20 gallon compressor that developed a pinhole leak. He wound up buying a new HF compressor and just used the new tank on his old compressor. He told me it was cheaper to do it that way than to buy a new tank. New tank cost at least $192.00
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post #12 of 13 Old 06-05-2020, 07:20 PM
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I'm not a mechanical engineer so I have 2 questions:

1) Could a motor and pump running continuously greatly over-pressure a compressor tank too the point of explosion? I would think that the pump has a certain upper level of pressure at which it could not exceed or burn up.

2) Wouldn't the over-pressuring have to be relatively instantly to completely blow every seem on a tank. That just dont seem right. Explosives yes, but air pressure pumps? I don't think so.

Anyway, it looked like the guy that got blasted might have suffered serious injuries, The man that came after him was scampering for what I believe was towels and rags to stop bleeding.

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post #13 of 13 Old 06-05-2020, 07:26 PM
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I sprayed a heck of a lot of lacquer so even though I had moisture traps and oil traps, I still shut down my compressor every night and opened the drain. Every morning, I would close the drain and turn on the compressor. Including the bending and standing up again, it was probably 10 seconds of my time.

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