Air Compressor Safety

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steamingon
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Air Compressor Safety

Post by steamingon »

Air Compressor Safety

www.youtube.com/watch?v=sm_FJ6Pat4I

Ooophs!
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Steggy
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Re: Air Compressor Safety

Post by Steggy »

The failure was predictable. The tank clearly wasn't being drained at regular intervals. His "failure analysis" is poppycock.
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Russ Hanscom
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Re: Air Compressor Safety

Post by Russ Hanscom »

Of course in NM I have to add water to the air tanks.

Not wise to repair pressure vessels unless you are qualified to do so.

Interesting the evolution in design and safety factors. My air tank has at least a 1/4" thick wall, is 50+ years old, and the allowable joint factor at the time of manufacture was maybe 0.7.

New tanks are exceedingly thin, probably 1.0 joint factor and pushing code limits.
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Steggy
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Re: Air Compressor Safety

Post by Steggy »

Russ Hanscom wrote: Mon Feb 01, 2021 12:20 pmOf course in NM I have to add water to the air tanks.
You mean to tell me there is water in NM??? :shock:
Not wise to repair pressure vessels unless you are qualified to do so.
Even then, it's not wise. Welding always changes the metallurgy of the base metals. It's not possible to anticipate what those changes might be unless you know the chemistry of the steel and how it reacts to localized heating above the transformation temperature. Best thing you can do with an air tank that needs repair is to weld shut the holes and convert it into a big BBQ grill or a smoker. :D
Interesting the evolution in design and safety factors. My air tank has at least a 1/4" thick wall, is 50+ years old, and the allowable joint factor at the time of manufacture was maybe 0.7.
My compressor—assembled from parts—has an 80 gallon, ASME-code, horizontal tank rated for 200 PSI maximum (shut-off occurs at 150 PSI). I purchased that tank in 1990 and a few years ago, had it ultrasonically tested for integrity. It passed. During testing, the inspector advised me the tank was fabricated with 3/16" thick steel, which he said was common for tanks of that size. He also noted that the material thickness at the bottom was essentially the same at the sides and top, which implied that corrosion was negligible.

When I built the compressor, I fitted it with an electropneumatic condensate drain valve that is held open for a few seconds each time the compressor starts (the air blast is piped outside the building and never fails to scare anyone walking past). I'm sure that is why the tank is still in excellent shape after nearly 31 years of service. I also have a filter-drier on the output of the tank to capture moisture carried in the air flow. It's annoying when your impact wrench or angle grinder starts blowing white bubbles while in use. :D
New tanks are exceedingly thin, probably 1.0 joint factor and pushing code limits.
Better fabrication methods and the automated submerged arc welding process have made the use of lighter materials practical, reducing cost. Of course, a thin tank can rot out faster if frequent draining doesn't take place. Unfortunately, most hobby-grade compressors don't have provisions for automatically draining condensate at regular intervals, which means failure becomes a matter of "when," not "if."
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SteveM
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Re: Air Compressor Safety

Post by SteveM »

Neighbor gave me a compressor similar in size to that one. Older cast-iron pump - the kind that can go forever.

Tank was a little iffy looking so I ditched it and picked up a larger upright tank from a compressor that had the pump fail.

It's much newer, and while the pump is not the correct size for that size tank, I don't use a lot of compressed air for long stretches, so it will do what I need.

Seeing this will make me think about where to place the compressor so that the blast would go away from where anyone is likely to be standing.

Steve
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gwerhart0800
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Re: Air Compressor Safety

Post by gwerhart0800 »

My father-in-law had a Sears compressor that he had "fixed" by putting screws into the rust holes. He owned/operated his own dump truck service and when the tank blew he was on the other side of the truck. Fragments punctured the tires on the side of the truck that the compressor was on. Had he been on that side, he likely would have been severely injured.
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liveaboard
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Re: Air Compressor Safety

Post by liveaboard »

yeah, that tank sure looked thin. No doubt suitable for use when it left the factory, but no margin for corrosion.
Sometimes I visit a shipyard in Holland with my boat. they have a big industrial compressor, and if I work late I drain the condensate and shut it down.
A LOT of water comes out, every day.

I like BDD's idea of an automatic drain. I should do that too; probably won't, but I should.
armscor 1
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Re: Air Compressor Safety

Post by armscor 1 »

I made a compressor enclosure OUTSIDE my workshop, no noise and well away from it should it fail.
Ran a 1/4" copper line from the drain to inside of my workshop so convenient to drain.
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Steggy
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Re: Air Compressor Safety

Post by Steggy »

The actual danger posed by a properly maintained shop air compressor is very low. I've worked around air compressors for close to 60 years and have yet to see one fail catastrophically. My rationale behind enclosing one in its own space would be noise abatement, not protection. A wall built from lumber and sheet rock is not going to do much to stop flying shrapnel should the tank burst.
liveaboard wrote: Tue Feb 02, 2021 9:20 amI like BDD's idea of an automatic drain. I should do that too; probably won't, but I should.
I used an electropneumatic valve as the drain valve. This type of valve is triggered by a solenoid that opens an internal pilot port that causes air pressure at the valve's inlet to actually unseat the valve. That way, the solenoid doesn't have to be all that powerful to do its job. The valve is piped into the drain port on the underside of the tank. A solid-state timer module driving a small relay sequences everything.

When the compressor's pressure switch commands the unit to start, the timer starts its cycle. It energizes the drain valve, discharging air from the tank to outside the building. After about five seconds, the timer de-energizes the drain valve and the motor contactor is energized to start the compressor. It's not complicated and can be done with off-the-shelf parts.
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tornitore45
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Re: Air Compressor Safety

Post by tornitore45 »

I have a HF vertical compressor. The drain valve is not on the very bottom. I have to tilt the unit to discharge the last bit of water. Chinese engineering.
Mauro Gaetano
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Steggy
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Re: Air Compressor Safety

Post by Steggy »

tornitore45 wrote: Wed Feb 03, 2021 5:56 am...Chinese engineering.
An oxymoron, if there ever was one. :D
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4gsr
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Re: Air Compressor Safety

Post by 4gsr »

Any air compressor tank found here in USA and most parts of the World has to have the ASME tag attached certifying it passed hydro testing at the factory. All tanks are 100% tested, no batch testing allowed that I'm aware. Safety factor at test pressure is 1.25:1, of course, it depends on what section of the pressure vessel code they use. So at normal working pressure, the safety factor is at 1.5:1. I do not believe tank manufactures (China) use a corrosion allowance factor in their calculations neither. There is a maximum life date allowed for a air tank. I don't know the codes enough to know what the life is for a tank. I feel anything over 50 years old needs to be re-hydro tested and recertified by a company that has the proper code stamp for this type of work. OF course, us home shop guys can safely do this ourselves provided we take the proper steps doing so. Anyone deciding to do this themselves should derate the maximum test pressure by at least 25-30% IMO. Ken
Ken
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