Draining air compressor tank

by Marc
(Rockford, IL)

I have a 60 gallon tank compressor and plan to use it occasionally in my home garage. How often should the tank be drained?

IS there any potential damage to be done if I leave moisture in the tank in freezing weather?

Thanks for your help.

Bill says...

Howdy Marc.

To questions one, the answer is that it's best to drain the tank after every use.

To question two, there is potential for problems. Here's more info on draining the tank.



Comments for Draining air compressor tank

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Mar 12, 2011
Manually draining
by: Anonymous

Mine's only a 21-gal "smaller" unit and as such also comes with a 1-stage motor, which I know from experience the longer it runs, the hotter it gets. As a rule they can run continuously for 15-20 minutes without too much trouble, but let it run much past 1/2 hour and you could be asking for a fried commutator (that would be the wound central axle of the motor, requiring a motor replacement).
For this reason I always monitor the unit and as I use it daily for maybe 5-10 minutes I simply can not afford to drain it completely.
With light daily use there simply isn't enough water build up, hence I drain it every so often and as another person pointed out, only until the water stops coming out.
This takes practice one, and if you decide to follow my advice you take your chances with a possible corroded tank interior two, but then again way I see things either way we're taking our chances (a fried motor costs as much as the entire unit, $140+).
So, that's just my .02

Nov 17, 2009
by: MEP1

There are two common types of auto-drains. One is a solenoid with an electronic timer that opens the valve for a short preset period every so many minutes or hours. The other is connected to the tube that runs to the pressure switch and opens the drain valve every time the compressor shuts off, and does not require any electricity to operate. They're both effective.

Nov 13, 2009
Draining a large tank
by: Anonymous

While I agree that you should drain the water from a tank every night as you turn the lights out in your shop, the article referenced speaks of completely draining the air and leaving the drain cock open. With a 60 gallon tank, that can take quite a while using the 1 inch dump valve, and draining it through the water drain cock can take a very noisy long time and is very wasteful of air. So i just open it long enough to remove the water, then close it.

For my 60 gallon tank, I have found an old (non-electric and automatic) < a target="_blank" href=http://www.kingstonvalves.com/products/unloadervalves/620-3.html> compressor tank drain valve that I hope will be a better solution. (Or maybe a different solution? .ed)It comes on for a few seconds each time the compressor starts and stops to drain the tank automatically.

Bill responds...

Thanks for this. I assumed that most of the questioners on this topic are owners of smaller compressor. You know what they say about assuming?

Your comments about the time to dump a larger tank, not to mention the energy waste, are spot on.

On a few pages on my site I refer to an electronic auto-drain for compressor receivers. These are very useful devices that regularly and automatically drain the tank of water, use minimal energy, and waste as little compressed air as possible.

I had not heard of the product you refer us to, and it is indeed very interesting. I edited your comment to remove the term "unloader valve" as it has a different meaning in compressor use.

Thank you again for your useful comment, and for visiting my website.


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Draining the tank make a difference?

by lisa C.
(red bluff CA)

Bleeding (draining) the air - does it really make a difference if I use it one day

My dad yells at me for using the air compressor because some times I forget to drain the air.

He says ..." The second you are done filling the tire or what ever...You better drain it"! "If you don't the tank will get condensation inside and it wont work".

Is this true...does it really make a difference if I use it one day and go back to a full tank in a week or so....or do I need to drain it and refill it each and every time?

Please help!! I dont want to get yelled at any more!


Hi Lisa...I sure hope you don't get yelled at any more either.

Perhaps it might help if you understood where the water comes from? See the page: www.about-air-compressors.com/water.html for information about compressor water.

Essentially, as soon as the compressor motor starts and air is being compressed into the tank, water is appearing inside the tank too.

So, when you've finished the compressed air-using work, the tank has water in it.

Hopefully the air tanks on compressors are coated inside to help prevent water from getting to the metal and rusting it out.

Unfortunately, I'm not convinced this is the case, so if you don't drain the water out, it sits in the bottom of the tank, and wherever it touches bare metal, rust starts forming.

Over time the rusting of the tank will weaken it, and it's possible that a leak might develop, in which case it's time for a new tank.

Also, the presence of water in the compressed air tank means that this water will migrate down the air lines to your air tools. This is not good for them, and will, in time, create air tool problems that will have to be fixed.

All because of water.

Lisa, your Dad is right. You should drain the tank after every use. This is preventive maintenance to help make sure you air compressor tank lasts as long as possible and to help ensure that the minimal amount of compressor generated water migrates down the air lines to the air tools as possible.



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should you leave air in idlle compresssor

by Pierre
(North Bay Ont Ca)

Air left in compressor for two months while idle

Bill says...

Pierre, the ideal scenario is to open the tank drain to bleed off all air, and all the water that has accumulated in the tank during use, so that the tank is dry while in storage.

Else, your tank will rust.

Does that bother you? Is the fact that your tank might get a rust hole in it faster if you don't drain it than if you do important?

Only you can decide.

Me, I try to drain my tank regularly, and only leave air in it, if I'm using it the next day.



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Oct 26, 2011
Leaving tank pressurized
by: Doug

So If at the end of the day compressor has been off for hours I would assume that the air temp had fallen to room temp. Can You simply open drain for 10-20 seconds to push out moisture and close up to save the compressed air for another day?

Is that OK to leave it pressurized and will not rust or is it best to drain tank completely to remove all compressed air even if it has cooled off and the water vapor has condensed to liquid?


Ultimately, the compressor tank will rust through regardless. By draining regularly, you defer the date you have to replace the tank or compressor. Electric auto drains do what you suggest by cycling open periodically for a fixed period. So yes, if you open the drain until water and mist stop flowing out, and if you still have air in the tank, close the drain to save the air. That's what I do.

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water generated inside a compressor tank

by john
(Gauteng South Africa)

Are there different designs of air compressors that will allow less water out of the compressor and into the air line.

For example, is there some kind of device that is fitted inside some compressors, (I would assume more expensive compressors), that would retain more water inside the tank and therefore send less water into the piping system.

Is there a way of checking, or asking the salesman if his compressor will allow less water into the piping system.
John, simple answer... no!

The amount of water a compressor generates has to do with its operating temperature, the cycle time, the air temperature of the air that is being drawn into the compressor, and the relative humidity of that air.

If you have water in your air lines, install an electronic auto drain for the tank (that will get rid of the water in the tank) and adequate water filtration in the air lines to your applications.

See the pages on Water on this site for much more info.



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Nov 21, 2014
Exploding compressor tanks
by: Bill

I absolutely agree.

If you start a new thread, you can upload your images then, and I'll move them to this comment if you wish.


Nov 21, 2014
Compressor Tanks can explode
by: Anonymous

I work for a manufacturer of Condensate traps for air compressors so when my girlfriend who does workmans comp claims was handed a claim about a man who lost much of his intestines due to an air compressor explosion she shared it with me. The pictures shocked me. I was going to share the pictures but this site did not let me post the PDF. The explosion was caused by the tank rusting and the walls of the tank became very thin. Please drain the moisture from your tanks or add a condensate trap to do it for you.

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