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Stored Energy in the Air Compressor

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David Paule

Well Known Member
I just looked up the formula for the stored energy in the air compressor's tank. Turns out to be quite a lot - more than 192,000 foot-pounds of stored energy. It's enough to lift my pick-up truck about 38 feet in the air, and I don't imagine it would be much good as a truck after that.

Guess I'd better be careful around that thing!

I used the equation here, if you're interested:
http://www.lbl.gov/ehs/pub3000/CH07E.html

Dave
P.S. Apologies for abusing one of Lincoln's jokes....
 
I had an old heavy commercial 30 gallon horizontal air compressor in my garage years ago that I scavenged from an old Sears Auto shop . I did not know it but turns out that the safety release valve was corroded frozen and there was a problem with the pressure switch that developed on this occasion of use It was mounted under my work bench against the back wall. I was doing some spray painting with it (tractor) and not really paying attention to it. When I finally realized that the compressor was running constantly and not cycling On/Off, just about at that time it exploded. The tank split open at the weld seam. The electric motor and the large 2 stage compressor ended up way out in the driveway, the back wall of the garage was blown out and sent broken studs and wood siding 100' behind the garage, work bench was trashed and after I regained my composure realized that fortunately I was OK! I now do regular inspections of my 7 hp 80 gallon compressor in the shop: Drain tank of moisture weekly, test pop valve, ect. I also never leave any hoses connected at the end of the day and I turn off the breaker when we leave for a trip or will not be in the shop the next day.
 
heh heh... makes me remember blowing up a scuba tank once goofing around with the guys. I used to run a high-pressure air service company handling paintball fields, scuba shops, emergency responders etc - and I had the capability of generating 25,000 psi of air on my mobile trailer. One evening after a few rounds of drinks one of my buddies challenged me "Bet you can't do this..." and you know where it went from there.

Anyway, it turns out an 80 cubic foot standard aluminum 3000psig rated scuba tank will unzip itself rather dramatically at 7200psig. We found about 2/3 of the mass of the shrapnel within a 400-yard search, the rest was gone. I'll have to run the calculations tomorrow just for grins, I know it was a lot of energy....

1000426j.jpg


Anyway, back on topic - yes, there is a LOT of energy stored in compressed air. Caution is advised, and don't ever trust PVC for compressed air plumbing in the shop.
 
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truck Tires

I dont know if they still have these, but commercial truck tires (think vans with 80 PSI tires) used to have a split ring on the wheel, I guess because you couldnt stretch the bead when mounting high pressure tires. Safety engineers always wanted mechanics to perform the initial inflation of the tires inside a tubular steel cage, in case the ring wasnt seated properly and popped off. Apparently, the ring could leave the wheel and was well positioned to cut the mechanic in half. You guys are lucky.
 
Hmm. Makes me want to re-think my habit of leaving the compressor both plugged in and turned to "Auto" so it's always full when I need it. I guess I can live with the initial startup time when I need air. The alternative sounds a lot more painful.
 
Snowflake said:
Hmm. Makes me want to re-think my habit of leaving the compressor both plugged in and turned to "Auto" so it's always full when I need it. I guess I can live with the initial startup time when I need air. The alternative sounds a lot more painful.
Click to expand...

I remember reading a post cautioning against leaving the compressor on AUTO, mostly for fear that a leak can occur when you are out of the shop (or out of town), causing the compressor to turn on indefinitely. Obviously, bad things can happen if the compressor motor runs non-stop for an extended period of time :)

Incidentally, if you don't have any leaks in your lines, turning your compressor to OFF, leaving it for days/weeks, and then returning to it should not cause the motor to turn on and cycle...since the tank is already at the PSI you left it at when you turned it off. But, it is not recommended to leave your tank full for fear of corrosion...so its a moot point.
 
Danger in compressed air

My younger brother Terry Darley, an avionics tech extraordinaire, was killed when a corporate jet tire rim exploded and ruptured his heart when the rim hit his chest. Use caution!
 
David Paule said:
Not if you drain it once a week.....

Dave
Click to expand...

In my shop, I set up a circuit on my air compressor that triggers a 1-second timer (just an old ice-cube relay for you old-school electronics guys) each time the compressor shuts down. That one-second timer holds open a solenoid valve that is in place of the bottom drain on the tank, and vents any water in the tank through a .068" orifice outside through the shop wall via a 1/4" copper line. 1 second of 125 psi air will not move a lot of volume through a .068" orifice - but since it activates on EACH shutdown, it only has to move the amount of water that will condense during one cycle.

I didn't even bother to try to do the math on this - but I know from checking it that it's more than enough, I don't have any water in the bottom of the tank. Works for me, YMMV.
 
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