Automatic Compressor Drain
By Paul Lapczynski
Like a lot of people, I often forget to drain my air compressor. It’s not a big enough problem that I’m gonna shell out for a high-tech, high-dollar automatic compressor drain, but I’m willing to give this low-buck Harbor Freight version a look.
First you have to cut into the high-pressure line to install the auto drain. Once it’s installed, whenever the compressor cycles on or off and the valve notices a difference in pressure, the auto drain releases a small burst of air from the compressor.
This automatic compressor drain sells for about $10 at Harbor Freight. Other manufacturers make electric-powered versions that run from $80 to several hundred dollars — you can find those by following the street pricing link below.
Automatic Compressor Drain [Harbor Freight]
Street Pricing [Google]
February 10th, 2009 at 10:43 am
I have one of these on my compressor tank. It works as described, a small blast of air out the drain valve every time the compressor turns on or off.
Mine lasted a couple years before it started leaking. When it did, I just bought another kit and replaced the valve portion.
The only real caveat to it is that the drain valve sticks out the bottom of the tank by a couple of inches. It may be needed to raise the tank up a little bit to get enough ground clearance for the valve.
February 10th, 2009 at 2:02 pm
Maybe I’m missing something, what is the benefit of one of these things?
February 10th, 2009 at 2:36 pm
@Partick
So you don’t get a puddle of water in the bottom of your compressor tank, rusting from the inside.
February 10th, 2009 at 3:24 pm
I wonder if this could somehow be fitted to an air line. In our shop (60′ x 120′) we have 3/4″ black pipe air lines with strategically placed pipe nipples to hold condensation. Right now, in order to drain them, we have to depressurize the whole system and remove rusty caps from the ends of the nipples.
February 10th, 2009 at 4:11 pm
BC,
Could you just install ball valves in place of the caps?
February 10th, 2009 at 5:00 pm
Would a “small burst” be enough to purge the water from the tank? When I’ve used my compressor a lot over a whole day, I’ll get a pretty big puddle when I drain it.
February 10th, 2009 at 6:32 pm
I drain my pancake compressor every couple of months have it on my calendar, although I’ve never gotten more than an oz or two after that amount of time.
I do it thought because I’ve seen problems first hand.
Where I used to work we had a humidity chamber on the production line for testing our hygrometers. It had a compressor with a little five gallon tank that was under 150psi. The humidity generator ran at least 4 hours a day and the compressor ran pretty much continuously.
On day I get a call from production saying the humidity generator wasn’t working right. The first thing I check was the drain valve on the tank, which was supposed to be checked every day. Well evidently it wasn’t because water started streaming out of it. So I stopped draining it and got a bucket. I drained about 3 gallons of water from the tank…no kidding.
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I’ll have to look into one of these when I get a proper compressor.
February 24th, 2009 at 12:50 pm
Joe, it operates every time the compressor cycles, so unless you’ve got an undersized compressor that runs continuously, this will drain many times throughout the day.
The pressure switch that controls the compressor’s cycling also has an “unloader” that depressurizes the cylinder so the motor can start next time it’s needed. It’s the hiss you hear whenever the motor stops. This hooks into that line, and it’s that pressure drop that triggers the mechanism.
April 29th, 2009 at 12:24 pm
Greetings.
I have been researching a dedicated air compressor system for my shop (permanently mounted compressor and plumbed airlines) and found a good review of the Harbor Freight auto release system here: http://www.paragoncode.com/shop/compressor/
The authors caveat has to do with the plastic line - he recommends upgrading it to copper.
BTW: It looks like you can “vent” the outflow from the valve if you live in a higher humidity climate.
Thanks
July 5th, 2009 at 1:01 pm
I have one and it’s worked fairly well for over a year. It did need to have the petcock cleaned out once, since the old rust was eventually all excreted. I bought two on sale because they were really cheap. One is a backup or may get installed on new compressor. Honestly, I can’t buy the brass parts for less than what they sell an entire kit for.
Anyway, a big plus of this system is that it depressurizes the compressor piston on the “blow-off”. So you can kick in the compressor whenever you like (back pressure relief). Some compressors won’t start (starter cap, long power cord, head pressure, etc.) unless they get below ~80 psi. I have tools that won’t work well unless they run at 90 to 100 psi. So it now keeps me from bleeding off 10 to 15 psi down to the restart threshold.
July 5th, 2009 at 1:07 pm
One more thing. Yes it required me to raise my compressor. But it was a project worth doing since I upgraded to some of those HF knobby tires to replace the hard-rubber wheels and beefed up the axle. Makes it a breeze to move now.
I use an aluminum pie pan underneath to catch any of the water. At first it spewed plenty of water and rust. But a good time afterward you can can hardly notice any water. It’s doing it’s job. And it reminds me to eat some pie and put a new pan underneath.