Air Compressor Drain Valve Mod

Failed and rusty drain valve.

Failed and rusty drain valve.

So. This is apparently a pretty common problem. After a long day in the garage, you go to drain your air compressor tank. Air and muck shoot out and you go in. And the next time you try to use the compressor, you can’t get that worthless little valve to seal to save your life. Eventually, these little things rust enough to not seal anymore and you get a constant leak. Pain in the ass, but at least just about every hardware store sells replacements. $3 and you’re back to compressing air day and night.

But what fun is that?

Answer: No fun at all, precious. No fun at all.

$30 worth of stuff to fix the $3 problem

$30 worth of stuff to fix the $3 problem

So here we go. Spending $30 to fix this problem is much more fun than just replacing that worthless little valve with a new one. And Scorponok agrees. He gravitated right to the new ball valve that I got to replace the little twist drain.

Right, some details. I’ve got a Craftsman (made by Devilbiss) 150 psi “Professional” air compressor. 25 gallon I think? Anyways, it’s a pretty standard model. And since I’ve only seen one model of little worthless drain valve on the pegs at the hardware store (1/4 NPT), I’m gonna guess that this parts list will work for anyone.

  • One 1/4 NPT ball valve.
  • One 1/4 NPT elbow. I chose male to female.
  • A couple assorted 1/4 NPT extension tubes. Male to male. I bought a 3″ and a 2″.
  • One 1/4 NPT to 1/4 ID barbed hose adapter.
  • PIPE SEALING COMPOUND! – Forgetting this caused me to go back to the hardware store.
  • A short length of 1/4 ID rubber hose.
  • And if your tank doesn’t have a 1/4 NPT drain, you’ll need an adapter. Or to buy all this stuff in 3/8 or 1/2.
My assistant tests the ball valve.

My assistant tests the ball valve.

First off, you might want to lay your air compressor on the side. I’m sure it’s possible to do this while the thing is sitting on the wheels, but I’m not one for too much punishment on a small project like this. I have a Miata for those confined-space projects.

Next, screw on your elbow. It should end up pointing to the side you want your ball valve to sit on. And into the elbow, you should attach the extension to allow the ball valve to be accessible without you having to move the tank around a lot. 2″ was perfect for my tank. I can reach the valve, but it doesn’t stick out in shoe territory.

Then you screw on the ball valve.

It’s easier to do all this stuff than type about it.

Ball valve air tank drain all assembled.

Ball valve air tank drain all assembled.

Once the ball valve is on and you’re happy with the fitment, go ahead and screw on the barbed hose adapter. Then attach the hose and add a small hose clamp.

Why are we doing this? Well, you could just add another small extension tube to the end of the ball valve, but then the air would blow straight out across your shop floor. Also, you could add an elbow to make the air blow down at the floor, but then you’d end up spraying pebbles and dust into your face whenever you bled your tank. With the little hose, you can direct the air wherever you want. I tend to use mine to dust my workbench.

Keep in mind that yucky, rusty water tends to come out with the drain valve air. That’s why you drain the tank in the first place. I don’t dust anything of consequence with this air. I don’t dust my car with it. More often than not, I’ll just wrap a big dirty towel around the hose coil and let the tank slowly drain at the end of the day. The towel keeps the hose from zooming around on its own and sponges up the dirty water.

Last step: Fill the compressor and check for leaks.

Last step: Fill the compressor and check for leaks.

And if there are no leaks, then it’s beer time.

A happy air compressor with a spiffy new drain.

A happy air compressor with a spiffy new drain.

It really works great. The ball valve turns this annoying task that I’d do about once every ten tank-fills into something almost fun. Almost.

Wave bye-bye, Scorpy.

Wave bye-bye, Scorpy.

Happy compressing!

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  • […] Air Compressor Drain Valve Mod . May 24th, 2010 | Tools & Garage. Failed and rusty drain valve Here is the original post: Air Compressor Drain Valve Mod — […]

  • cna training says:

    What a great resource!

  • How often do you drain your Air-Compressor? says:

    […] How often do you drain your Air-Compressor?

  • Jeremy says:

    That is indeed a happy compressing tips and procedure you have shared. I must say Air compressors are one of the most important pieces of equipment a shop or a household can have. The best thing about it is that it can be used to power tools, inflate tires (my wife just love this function), and clean my mini workshop in the house.

  • Dana says:

    Too awesome.

  • airaudit says:

    Thanks for sharing such a useful information with us …. I like the way you describe the post with us. Many thanks

  • Bobby says:

    Just wanted to say thank you for posting this… I have the stand up version of this compressor and it’s in a tight spot so getting to the valve was almost impossible without moving and tilting the entire compressor. Using this, I was able to make a painless trip to home depot and had the entire project finished in less than 30 minutes. I used a 5″ extension to make reaching the ball valve easier, but everything else mimic’d your setup. Thanks again!

  • […] harm the tools so much, but im more worried about it mixing in the paint. Im going to try this Air Compressor Drain Valve Mod — to make it a little easier. It is a pain to go under it and drain it. + […]

  • Oliver D. says:

    I have the stand up model of this compressor and this mod was well worth it. I spent a total of $24.00 at Ace Hardware, then came home and installed the items in 25 minutes.

    This link is the first one on Google, when you search “adding drain valve to air compressor”. I will tell my friends to do the same mod to theirs…..

    • revlimiter says:

      Glad the post helped you! This reminds me that I need to drain my tank. I’ve not done it in a couple fills…

      And awesome about the google status! So many people being exposed to toy photography. lol

  • Kisershop says:

    Thanks for the information and article. Both my dad and I needed this fix for our pancake Porter Cable compressors.

    Great work!

  • Will says:

    Thanks for the helpful article! I’ve just followed your example and bought the parts to do mine off Ebay. The only difference with mine is that, because I’m in England, the threads were BSP instead of NPT! All in I’ve spent £14 (~$23) and I think it’s worth every penny just so I don’t have to fumble round on all fours trying to undo that stupid drain fitting after a long days grit blasting!

  • Tim says:

    This is a very smart thing to do and I am surprised how many model don’t have this feature ready. Great tip and relatively easy to implement. Thanks

  • Jeffrey Warnocj says:

    Thanks for the tutorial and parts list…very thorough! I just put this on my 20year old Craftsman 25 gallon compressor. I brought your list to my local hardware store and the employee there found all the pieces I needed for the mod.

  • Vince says:

    Good idea! Ebay has ball valves for just a few $, most compressors have 1/2″ connections (mine does), so basically all you need is one valve and one hose.

    I recommend copper greasing the components that screw into the tank, to prevent any crud building up on the valve inlet. Also thread lock the 1/2″ thread.

  • Ron says:

    Thank you for sharing this…I had mine break off in the Craftsman. Someone put me onto the nipple extractor for removal of the small piece – worked..after a few raps with a small sledge hammer! I installed your model, less the hose – what a relief.

  • roger tu says:

    I have a Dewalt Air Compressor – portable. My tank has rust slurry in it and I need to clean it out. Is there a recommended method to flush a small air compressor tank?-

  • Abner says:

    That is indeed a happy compressing tips and procedure you have shared. I must say Air compressors are one of the most important pieces of equipment a shop or a household can have. The best thing about it is that it can be used to power tools, inflate tires (my wife just love this function), and clean my mini workshop in the house.

  • Doug says:

    Some compressors have a fitting with a small ball in the fitting. If the compressor is not drained often enough, the rust and oil will plug the fitting and you will be unable to blow out the moisture. We normally just put a pie rag on the floor to catch the rust and water. It is not needed to open the valve all the way, just enough to get rid of the water.

    And do not forget to change the oil once a year. Assuming you do not have an oiless compressor.

  • Arved says:

    I did this a few years ago to my Sears Craftsman 6HP compressor with the 25 gal. horizontal tank. Same model? I put an elbow after the ball valve to direct the air and water downward, and put a cookie sheet underneath to protect the concrete floor so it wouldn’t stain from the rust. You don’t need to crack the valve all the way open to get enough flow to purge the water from the tank.

    Those cookie sheets come in handy.

    How often? Once when I turn the compressor on, and again when I turn the compressor off at the end of the day. There are automatic drain valves that cycle every time the compressor cycles. Many have good luck with the Harbor Freight automatic drain. I didn’t. Leaked like a sieve. I tried tightening it to fix the leaks, but ended up cracking the housing. The tube between the relief valve (between the compressor and tank, so the compressor doesn’t start fighting full pressure from the tank) and the drain valve is a weak link in the system. Plan on replacing it with copper icemaker tubing. But the automatic drain valve should give you an idea of how often to drain the tank – every chance you get isn’t a bad idea!

  • Charles says:

    I’m using the petcock the compressor came with. I slip an old aluminum pie tin under it to catch the water. The most I get out of it is about a teaspoon of water.

  • Greg says:

    Not only helpful, ENTERTAINING!!

  • Nancy says:

    I put the ball valve on my Craftsman upright 150 psi 6hp air compressor after the factory valve failed. Now I don’t have to lay on the floor with vice grips to open the valve and close it! Thanks a million!

  • I got to tell you that you are the charmers) Useful air compressor info)Thanks a lot

  • Great article. I’m a car lover so I don’t dust my car. I think your info will make me more careful of my car.

  • Rebekah Purnell says:

    So helpful information. As a car owner, I will follow your tips. Thanks

  • The automatic drain valve manufacturers by Trident provide a spectrum of auto drain valves to its clients which effectively purify air by eliminating pollutants.

  • Mitchell Findlay says:

    I am planning on buying a new air compressor with automatic water draining feature. When I drain my current compressor the water coming out is brown and stains the concrete floor. Since I have a sink nearby, can I put a hose on the drain valve and direct the air/water/oil into the drain piping above the p-trap but below the sink?

  • Tex Hooper says:

    I didn’t know that ball valves were available. My compressor has a blockage. I’ll have to order a replacement part.

  • Burnice Bauch says:

    Thank you for sharing such an insightful article. Hope to read more content just like this in the future.

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