air tank auto drains

by Ron
(Rochester, N.Y.)

I have read and reread your section on auto drains. You refer to a auto drain with a float ball and drain.

Please excuse my lack of knowledge on this subject. I checked your references to vendors for the electric and float versions, but have not seen any reference to the automatic type that use the compressor cycle to drain it each time the compressor shuts off.

Harbor Freight offers a automatic drain valve that is plumbed to the feed line at the top of the compressor. It is spliced into the side of the line that is cutoff from pressure when the pump cycles off. It is usually a short drain cycle (3-4) seconds, but works each time the compressor reaches it's shut off setting.

I'm looking for your opinion and any experience with this type of auto drain valve. Pro's and Con's.

I have a older (20+ years) Craftsman 6 hp-33 gallon horizontal oil less compressor that was purchased new and sat for 5 years before I acquired it. I think I was the first user so about 15 years intermittent use. I plumbed it with this type drain valve about 10 years back. I always find a stain spot under the compressor where the drain valve is located, when I move the compressor to clean or sweep.

It seems to work OK. Occasionally I will hear it spit-discharge when the compressor starts up from being completely empty. The drain valve has never stuck open. The hoses and connectors will allow the compressor to drain the air completely out over a day or two. Other than having to completely fill the tank from empty each time the compressor has worked flawlessly.

Thanks for sharing your experiences!

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Dec 31, 2014
auto drain valves
by: Ron

I was just curious if anyone else had the experience of using this type of auto drain over a extended period of time.

Having driven and worked around tractor trailers rigs for over 35 years, I have experienced what you mentioned about the drain valve that used to be equipped on trucks. Most of them would freeze up in the winter and usually freeze open. The newer systems are all 12 volt controlled with a air dryer built into the system. Still not trouble free, but much better than the old set-up.

My compressor is in a unheated garage and draws in air at the temperature of the garage. Obviously the compressor generates heat and creates moisture in the process. My experience with this type of valve is limited to the one compressor I own. As my compressor is getting past the 20 year mark, my concern is the over condition of the inside of the tank. I use it infrequently and it sets empty most of the time.

The simplicity, cost and small size of the auto drain were what impressed me. The cost and required electrical hook up seem more designed for a compressor that is used all the time or at least frequently.

Dec 31, 2014
permanent piped air system
by: Bill

Re "permanent piped air system" actually, not quite correct, Doug.

An electric auto drain is used to drain the compressor tank, or any other vessel, where water can condense from the compressed air and accumulate.

If one is using their compressor a lot, and particularly if they have installed the compressor and tank in a harder to reach spot, then an auto drain installed on the tank will be very useful to ensure that the tank drains on a regular basis.

As I recall, it does say that in spots on this site.



Dec 31, 2014
auto drain
by: Doug in

I've never myself gotten around to putting one of those on, but it's the same type thing that makes the psssht noise on air brakes. I have had one of those stick open, and it'll disable the vehicle when it happens. But it is pretty rare.

The only problem I've heard of with the HFT thing is the tube they supply will soften and pop off on some compressors. Use copper tube to replace, and it's all good.

The ones on this site are mainly for use downstream on a permanent piped air system.

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