Leaving Air Compressor Full

[Buck Turgidson]

Partially out of laziness, inertia, procrastination, and partially because I use it several times a month, I leave my Porter Cable air compressor full. Does this do longterm harm to the machine?

[lwhaley]

no

[Doug]

I've been led to believe that the compressed air will create moisture/ condensation in the unit which obviously can do damage. I usually try to remember to bleed mine.

[Jedd Haas]

Porter Cable's instructions say to bleed it every day. I thought that was a bit excessive, and left mine full for quite a while. The other day, I emptied it, thinking some water might have built up. Indeed, holding it up so the exhaust was at the bottom, a considerable amount of water came out! Had to hold it over the sink. Perhaps I'll empty it like that every few of weeks now.

[scouter3]

Condensation building up in the tank, causing internal rust, eventually leading to tank rupture, is a long term possibility. Compressors have a drain valve on the tank for this reason.

[Lew Hodgett]

Yes and no.

Typically, the smaller the compressor, the less efficient, and the more condensate it generates.

Not emptying the tank and bleeding off the condensate on a frequent basis leads to problems.

Lew

[Leon]

You are on the right track. Actually the compressed air does not create the condensation. It is the heat generated from compressing the humid air that causes the condensation. Take a glass of ice water out into a hot humid place and you will get condensation on the outside of the glass. Once a compressor has stopped running and cools the condensation stops. The longer the compressor runs and the more heat generated the greater the condensation. Soooo, if you let the compressor cool and bleed off just the excess condensation there should be no more water build up when the compressor sets idle. Typically however, no one remembers to return to the compressor to bleed the condensation after the compressor has cooled. Bleeding is a good practice and total bleeding insures that you don't have to stand around waiting for all the water to blow out. Typically also, the faster and fewer times a compressor cycles the less build up of condensation you will get regardless of the volume being compressed. If you fill an empty tank form a cool compressor tank that is not running, there will be no condensation generated.

[Lowell Holmes]

[Lowell Holmes]

I just disposed of one (an old one) that rusted through. It manifest itself through a pin hole leak in the bottom of the tank. I think if it had been bled properly through out it's life, it would still be here. If the condensate is rusty color, you know it is rusting.

I never leave air in my pancake compressor now. The pancake is easy to drain. The old tank required getting down in my knees and looking under the tank. I should have piped the drain to a valve located in the open where I could see it. I would have drained the tank more often.

[Mortimer Schnerd, RN]

Compressed air doesn't create moisture; it only compresses what already exists in the atmosphere that day. The process of compression creates heat, which will allow more moisture to stay in the vaporous state. Later, as the tank cools down, that vapor may well condense since cool air can't hold as much moisture as warm air.

As a former scuba instructor, I'd always taught my students to never let a tank run completely empty as positive air pressure kept moist ambient air from entering the tank. However scuba air is MUCH drier than shop air. Given that shop compressors don't usually filter out moisture as scuba compressors do, it's a bad practice to just let that moist air sit in the storage vessel, rusting it out over time.

Bottom line... it's probably better to dump the air when you're done... at least for shop compressors.

[DouginUtah]

I have a 2 HP, 20 gallon Craftsman compressor. I drain it about every five years and never release the pressure at the end of the day.

I have been using it since 1973.

It was getting really hot when shingling so I changed the oil last fall. Don't know if that helped--maybe I just slowed down a bit. :-)

[Leon]

If you lived anywhere near the coast your compressor would have filled with water in a couple of years.

[Tom Veatch]

Or:

something similar

[Mortimer Schnerd, RN]

Maximum pressure 100psi? Make it something similar...

[Larry W]

Drain any condensation out after each use but there is no reason why the tank can't be left pressurized.

[B A R R Y]

I leave my own compressor full, and know of some that have been full for 15 years.

[B A R R Y]

Removing water is totally different than letting out the pressure.

[Doug Miller]

Incorrect. It is *exactly* the compression that causes the condensation: water that is vapor at ambient pressure can be condensed into liquid by increasing the pressure.

Increasing temperature *cannot* cause condensation; quite the opposite, in fact.

Yes, that's because the warm water vapor in the air is being *cooled* by the cold glass, and condenses onto it. Condensation is the result of a decrease in temperature (that's why dew appears overnight, not in the middle of the day) or by an increase in pressure.

Again incorrect. As long as the pressure remains high, the vapor will remain condensed.

Once again incorrect. It's the pressure, not the heat, that condenses the vapor.

Still off the mark.

Nonsense. The amount of condensation depends on the amount and humidity of the air being drawn into the compressor, and the pressure to which it is compressed. Nothing more. It has absolutely no relation to the compressor duty cycle.

That's because you're *reducing* the pressure. It has nothing to do with the temperature.

[Doug Miller]

How does the efficiency of the compressor make any difference?

[SWDeveloper]

Maybe. When you drain it do you see water? Water (and oxygen) will rust the inside of the tank.