Knob on 921.153101drain valve turns forever. Open or closed?

by Cheryl
(Boca Raton, FL USA)

Hello Bill,

I can't find an answer to this question anywhere.

Craftsman 3 gallon, 1.5 HP, uses oil, Model No. 921.153101

The knurled knob on my drain valve will NEVER stop turning. Whether I am turning it counterclockwise to drain, or clockwise to close, it can be turned 100 times and never come to a stop. Nor does it appear to move up and down (or in and out); always looks the same.

I can always tell for sure if it's closed because the tank will build pressure. But I can't always tell for sure whether it's open enough to drain. Sometimes I may only have used it for a few minutes. So if no water drips out, I don't know whether there is none, or I didn't turn the valve enough times! Is there a way to tell?

This is the first time I've owned/used an air compressor. I bought it from Sears a few years ago, and have only used it about half a dozen times so far. But I expect to use it much more now, and want to take good care of it.

Thank you,


Comments for Knob on 921.153101drain valve turns forever. Open or closed?

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Jul 03, 2018
Knob on 921.153101drain - and furthermore...
by: Doug in

you don't want to get the part from Sears. And you don't want that part anyway. They tend to leak, and are hard to operate.

Get a ball valve. 1/4 turn to off or on, and you tell it's open or closed.

Also, that valve is not at the bottom of the tank. Try tilting it with the valve open. There's a good chance more will come out. If it does, then you want to tilt it every time you drain it.

That said, "some" tanks have a tube that goes to the bottom of the tank, so all the water comes out without tilting. Yours may have that tube, but likely not.

Jul 03, 2018
921.153101 drain valve
by: Bill

Hi Cheryl... quite often the tank drain valves are non-rising, essentially meaning that they don't move up or down, but the mechanism that opens and closes the drain inside the tank is what moves. So, you may not see any change outside at all, ever.

However, they should not turn forever so with that statement I would surmise that your tank drain valve has failed.

If not water comes out, and the tank fills with pressure, it has failed shut.

If you get even a dribble of water out with the compressor running, you'll get both some water leaking and, unfortunately, air too.

Time to power down, and if the tank gauge shows pressure, open the pressure relief valve to allow the pressure to escape, and get the tank drain valve replaced.

Depending on where your compressor is situated, you may consider replacing the tank drain valve with an elbow, and using some poly tubing, run a line out from under the tank to a small ball valve which, then, becomes the drain valve and will be much easier both to operated and to access.

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