Leaving Air Compressor Full

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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?
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no
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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.
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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.
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wrote:

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.
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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.
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Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

After reading your post, it reminded me of the fact that in order to bottle liquid oxygen, they have to cool *and* put it under high pressure to get it to condense to a liquid, but I never would have thought to apply this principle to an everyday compressor. Good info.
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So Doug, I suspect you believe it is the pressure from "your firm grip" on a glass of ice water that causes the warm humid air surrounding the glass to cause condensation on the cool side of the glass.
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In his case, it would likely be a glass of vinegar. It would be better if it was bourbon or something, maybe he'd lighten- the-fuck-up.
but alas... I said too much.
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Of course not. Vapor condenses as a result of being compressed, or cooled, or both -- but never as a result of being heated. Warm humid air surrounding a glass of ice water produces condensation on the side of the glass because the temperature of the surface of the glass is below the dew point. The water vapor condenses because it is cooled.
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Doug Miller (alphageek at milmac dot com)
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Doug wrote:

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.
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Mortimer Schnerd, RN
mschnerdatcarolina.rr.com
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On Thu, 26 Apr 2007 22:29:26 -0400, "Mortimer Schnerd, RN" <mschnerdatcarolina.rr.com> wrote:>Bottom line... it's probably better to dump the air when you're done... at least

Or:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?ItemnumberB221
or something similar
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Tom Veatch wrote:

Maximum pressure 100psi? Make it something similar...
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Mortimer Schnerd, RN
mschnerdatcarolina.rr.com
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On Fri, 27 Apr 2007 05:25:15 -0400, "Mortimer Schnerd, RN" <mschnerdatcarolina.rr.com> wrote:

Well, I figured it was worth 10 bucks to try it out. When I went to retrieve the URL, I noticed the 100psi limit. That may be new. I don't recall noticing that limit at the time I bought one several months ago. I run my 80 gal compressor at 135 psi shutoff and haven't seen any adverse effects.
Every few days, or whenever I think about it, I open the manual drain valve to verify that it's keeping the tank dry. So far, since installing the automatic drain, I've never had a drop of condensation come out the manual drain when I check it.
I'm satisfied.
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Tom Veatch <firstname_lastname AT pixius dot net> wrote:

I bought one of these from HF, when I bought a new compressor recently. I must have spent the better part of a day or so trying to figure out a way to install this. The main problem I ran into is with the air hose supplied and the compression fittings it uses. Basically there weren't enough parts there to splice this device into the system as they don't give you any additional compression fittings. On my compressor, there's a solid copper line running between the tank and the regulator. So I would need two more fittings to rework things so that the automatic drain valve could be tee'd in between the tank and the regulator.
I spent several hours trying to find more of those fittings locally, but none of the hardware stores had them and HF itself does not sell them. Perhaps a specialized industrial supply would have them, but after spending a few hours trying to hunt stuff down, I gave up and returned the device. The device itself probably works fine, but you'd likely need to dig up some other type of way to splice it into your system that uses some other type of fittings and hose. It would be nice if they'd supply additional male and female compression fittings with the device, even if that increased the price of the device by a few bucks.
In the end, I found it's easy enough to just open the drain at the bottom once a day and let it blow out the accumulated moisture.
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You need a Grainger item # 4KT04 I screwed around with the HF drain valve, two of them in fact, and gave up and spent the cash on this one. Easier to install, and it works. Greg
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Doug wrote:

Removing water is totally different than letting out the pressure.
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"B A R R Y" wrote in message

Ditto ...
I moved the drain plug to the end of a 3' length of air hose on my small vertical, where it is much more accessible.
The air hose holds quite a bit of water that would otherwise be in the tank, and, unlike the tank, is rustproof ... and gravity does the work.
It is a simple matter to open the cock slightly every other day or so and let the water in the hose squirt out, and draining the tank this way doesn't even cause the compressor to cycle on.
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Swingman wrote:
| I moved the drain plug to the end of a 3' length of air hose on my | small vertical, where it is much more accessible. | | The air hose holds quite a bit of water that would otherwise be in | the tank, and, unlike the tank, is rustproof ... and gravity does | the work. | | It is a simple matter to open the cock slightly every other day or | so and let the water in the hose squirt out, and draining the tank | this way doesn't even cause the compressor to cycle on.
Great idea - consider it stolen :-)
Thanks!
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto /
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Ditto.
Thanks
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