Automatic tank drain on this Speedaire compressor?

by Jeremy Farlow

I recently purchased a used speedaire compressor. It's a newish, but obsolete model and I'm not entirely certain of the exact model.

The specifications are: 80 gallon upright tank. Two-stage pump, 23.5 CFM @ 175 PSI. Three-phase, 7.5 horsepower, dual voltage, Dayton motor. This appears to be a superseded model of the current speedaire flagship compressor, which comes with an automatic tank drain. At the bottom of the tank is the standard 1/4" NPT street elbow, to a valve, to a 1/4" copper tube that runs to a diaphragm pressure regulator mounted under the pump. On the side of the regulator is another 1/4" copper tube in compression fitting that has been pinched off or cut. On the top side of the regulator and on the other side of the diaphragm are both a screw adjustable "pop-off" valve and an 1/8" tygon line running to the bottom of the pressure switch.
Firstly, is this an automatic tank drain system?
If so, am I right in assuming it's a pressure differential style system?
Where does the 1/4" copper line coming from the side of the regulator go? This line bleeds pressure constantly when the tank is full. Water and vapor do come out, but so does my tank pressure.

Thanks for any advice you may give,


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Aug 15, 2017
Obsolete automatic tank drain
by: Robert Castro

I'm not sure if you got your answer yet but I have the exact same Auto drain on my Compressor. I found out that it is obsolete and you can purchase the new updated version from Grainger. The new part number is CC1079015 it cost around $315.00. I have not yet purchased and replaced mine yet but I hope this helps you.

Mar 14, 2017
auto drain
by: Doug in

FWIW, I think you're on the right track - that's generally how they work.

Hopefully you'll get a good answer sooner, but the pix will help if it's been monkeyed with.

Good luck.

Mar 13, 2017
Automatic tank drain
by: Jeremy

I say regulator, because the part in question looks like a diaphragm-style pressure regulator. I will take better pictures next time I'm at the shop. Mostly I want to see if anyone on this forum has information as to how the Speedaire, non-electric, automatic drains work.

There are two 1/4" inlet/outlet ports below the diaphragm portion. Both had copper tubes that didn't connect to anything, one at the bottom and one below the diaphragm on the side. The top of the parr has an 1/8" line that connects to the pressure switch.

I'm guessing that when the pressure switch tells the compressor to cycle it also sends air pressure to the diaphragm opening the ports and allowing the condensed water to drain. I'm hoping someone here has first hand knowledge and can help me eliminate some trial and error.


Mar 11, 2017
Automatic tank drain?
by: Doug in

Could be, but I'm not sure I'm reading what you meant.

When you say regulator, do you mean the pressure switch?

It sounds to me that perhaps the check valve went bad and this was a lame attempt to fix the leak.

Can you get better and more pix of it?

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