Air Compressor Drain Valve Mod

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

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.

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.

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.

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

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.

Happy compressing!