Compressor Foolishness

[Mike OMelia]

I thought maybe I would not post this. Like anybody, I don't like being thought of as stupid. But, if it keeps one person safe, it's worth my dignity.

I decided to add a new dryer and regulator to my 60 gallon tank. Meant pulling various fittings etc. Tank was at 100 psi so I pulled the release valve. When it got to about 40 psi I started to loosen the quick release connector. When it came off, the tank released faster, of course. Then stopped at about 35 psi. Huh? I walked around the front to take a look, thinking I was doing something wrong. Then, it released again, shooting ice at me.

I'm an engineer and understand a adiabatic cooling. Guess I dropped common sense for a moment. No harm or foul. But I'm glad I did not look into the hole! The vapor in the tank would freeze at the exit point and create a blockage, then melt and blow out the crystals.

Oh well, stupid mistakes can sometimes help others not make stupid mistakes.

Be safe,

Mike

[Bill Bixby]

As someone whos only been into woodworking for a couple of years, these posts are always very helpful to me. Thanks for taking the time to do it.

[Mike OMelia]

There is an old party trick we used to do with CO2 fire extinguishers. Blow them into a large trash bag. It will create dry ice. After that first experience, it stopped 2-3 more times. All I did was wait, and it would blow out and continue. Ice crystals at that pressure can penetrate your skin. Luckily, I was fully covered. I think the moral is, when something unexpected happens, stop, think.

[Steve Rost]

Mike, thanks for the heads up!!! I have a portable compressor and seldom use it. When I do I always drain it. I never keep it pressurized. It will do the same, just never thought about it.

[Jeff Duncan]

I'm glad you posted as well. I was not aware the air exhausting could get cold enough for that scenario to happen.....now I do;)

JeffD

[Jim O'Dell]

Ditto what Jeff just said. In fact, my first thought would have been the opposite, friction of the air and the moisture in it going through the hole would get hot. But like you said, stop and think and it all makes sense. Thanks for the school lesson!!!! Jim.

[Mike OMelia]

Chances are good you will never encounter this issue in practice since the compressor tank designers use escape valves that do not allow the gas to escape fast enough for excessive cooling. On the other hand, if you bypass this technology (as I inadvertently did) by allowing the gas to escape directly from the tank via the main exit port, it could happen. Weird thermodynamic stuff. I mean, what good would a blower be if it iced up all of the time? Trust me, take that main connector off, and it really blows!!! Pass it through a somewhat constricted valve and you've got ice, if there is water in your tank.

[Ken Harris]

The event you spoke of Mike is same thing that occurs in air conditioning where in this case high pressure going though an orfice you have a dramatic pressure drop and the water vapor goes through a profound change of state.Glad you we're not hurt something only makes sense after it makes sense.

[Mike OMelia]

Frankly, I did not think air could do that. I understand the principle. I based my belief on the fact that I'd never seen my dust blower attachment freeze up. Lol. I forgot to add when the ice blew out with me in front of it, it felt like I was punched (not incredibly hard, but it still shocked me). Pretty sure if skin was exposed, I would have experienced bleeding or bruising.

[Ronald Blue]

Compressed air is often disregarded as capable of injury. I am not saying you disregarded it just that many scoff at the idea that it should be respected. I am glad it was only an eye opening experience and not an eye damaging event. Out of curiosity what was the approximate ambient temperature in your shop when this occurred? I work outside most of the time with air tools and experience icing once the temperature drops below 50 degrees unless I use air tool lube/anti freeze.

[Mike OMelia]

It was unusually warm, 60 deg. But very humid. The tank air was stable and at equilibrium with surroundings.

[jim hollenback]

Frankly, I did not think air could do that. I understand the principle. I based my belief on the fact that I'd never seen my dust blower attachment freeze up. Lol. I forgot to add when the ice blew out with me in front of it, it felt like I was punched (not incredibly hard, but it still shocked me). Pretty sure if skin was exposed, I would have experienced bleeding or bruising.

Actually the result you got is exactly what I would have expected. I first noticed this at a young age and it was great fun to make a big ice spot on the concrete under the valve used to drain the water from the compressor tank. It was a big valve, think hose bib. Really fun and amusing to an eight year old. I learned the reason in my high school physics class when we studied about gases being compressed and expanded. Perfectly dry air under going adiabatic expansion would not create the ice, but it would get quite cold and make a nice plume of fog as the air in the plume cooled the water vapor entrained from the ambient air condensed. But, of course, the air in the tank is not not dry. It probably is fully saturated, so the expansion will cause the water to condense out, and this liquid water will undergo a state change.

[george wilson]

Icing on valves sank the submarine Thresher.

[Patrick McCarthy]

Mike, I was sitting in the back of the class with Jeff and Jim; thanks for the head's up.