Saturday, January 29, 2011

Water Valve Seat Restoration

Pictured below is the inside of an elderly 1/2" copper pipe shut-off valve. Its seat is non-replaceable, and it's a bit pitted.

It's possible to restore these to a serviceable condition. The method outlined here largely precludes the use of a cutter that may chatter. You need two things.

First is a lapping tool that you can chuck in a variable speed portable drill. That's just a short length of 1/2" hardwood dowel with a shoulder turned at one end. Turn the shoulder so that you end up with a reduced diameter at the end of the dowel, that will just fit easily into the inside diameter of the valve seat -- 3/8" was correct for this valve.

Second is valve grinding compound from the auto supply. The stuff I have is Permatex No. 474G, Grease Mixed type. It's a moderately thick oily paste of abrasive particles. It's normally used for lapping the poppet valves in piston engines; it's just what's needed for this.

Here's everything collected and ready to go.

Apply the compound to the shoulder of the dowel and spin it in the valve seat. You'll need to reapply compound and repeat the operation several times to get results. After sufficient repetitions, you'll have the pitting eliminated from the top surface of the seat, but you may still have some pitting at the inside perimeter, as I did here. (Flush the valve out in a parts washer and blow it out with compressed air once you complete a course of lappings.)

For a seldom used shut-off valve, that's actually perfectly serviceable as it is now. I would like to be rid of that remaining pitting, though. That's where the countersink in the photo comes in.

I don't recommend using the countersink with a power drill here -- too much risk of chatter. Chuck the countersink in a suitable pin vise and turn it by hand as needed to clean up the pitting. When it looks as satisfactory as it's likely to get, you're done with the countersink.

You can still improve on it by making a second lapping tool, this one with a chamfered end rather than a shouldered end. Here it is after a final series of lappings with both lapping tools.

That should now be a valve that's fit for installation. Here's how the thing looks fully assembled.


As far as it goes, what I've presented here should work and be sound. But, I have to confess that I've yet to actually install and fully pressure-test an old valve like this anywhere. On this one, I'm a bit leery of the old conical stem-packing washer, and finding a suitable replacement for it may not be easy.

What I need to come up with is a reasonably easy method of temporarily installing these things on a pressurized system for testing. I'll append the outcome of that to this post when I get it done.

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