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We've got a setup very similar to the picture in the answer to this:

3 valve shower allowing flow to tub and shower

I've read some similar questions here, but none is just like this:

The washer, whether it be flat or domed, on the valve next to the seat wears out by being crushed all the time, by requiring more pressure each time to close the hot valve completely to keep it from dripping, trickling, or leaking eventually becoming completely destroyed so as to require replacement. The water continues to come from the tub faucet head, as the diverter is left in the neutral position when not in use. They will come from the shower head eventually if left in that position, or the third option...

Replacing the seat once caused this not to happen for the longest period, but I just checked it, and it's still looking great/fine.

Any ideas? Using a 3/8" L type right now. Maybe there is some other solution that isn't quite obvious, or maybe a special material that won't just become completely more crushed with each turn. This last one lasted like a month...

Here's what I could find in way of brand marking. It looks like a "DI" in a square, then the "CSA" mark (C wrapping around SA). Brand

Here's an image of the crushed dome washer

destroyed washer

Here's the new flat style (rotating out the dome), installed:

enter image description here

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    There are a lot of companies that brag about their washers having better durability, seal better, etc. You might look for a different brand to try out, there are blue ones, red ones etc. All available in 3/8 L, try a good plumbing shop instead of the "big box".
    – Jimmy Fix-it
    Commented Jun 9, 2018 at 1:26
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    I have a story but you must promise not to get mad. There was a guy, a tough guy, whose tub faucet seat was bad. He had to apply increasing torque to get the washer to seal on the bad seat, so it would not drip and drive him crazy. The plumber came and changed out the seat and washer. The guy (remember, tough guy) continued to torque the handle like he was in a carnival strength contest, destroying the washer in short order. If only he would apply just a light touch after changing out the washer, he would see that it was all that was needed to have a drip-free closure.
    – Jimmy Fix-it
    Commented Jun 9, 2018 at 1:26
  • @JimmyFix-it that's a great story... indeed. Made me laugh, so automatic +1. If only all users of the shower could maintain the feather touch, but I'm not even sure you could close it all the way without slightly -more than- the washer can handle without starting the wear. Will be getting some new seats and try some other brands of washer... thank you!
    – NOTjust -- user4304
    Commented Jun 9, 2018 at 21:21
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    How hot is the water? Very hot water would make crushing a washer very easy.
    – Kris
    Commented Dec 30, 2019 at 0:45

1 Answer 1

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That washer presses up against another surface called the "seat" inside of your valve. If that seat becomes damaged or there is a buildup of corrosion on the mating surface, it tears up the rubber very quickly whenever you close the valve. Some valves have a replaceable seat. You need a special tool to remove that seat, but they are relatively inexpensive. See the picture below. Valve seat removalenter image description here

The thing is, some people wont buy that tool no matter how cheap it is and attempt to remove the seat by jamming in a screwdriver or something. That seat is soft brass, so if the screwdriver can't do the job and slips in the hole, it creates even rougher edges. They give up and resign themselves to replacing the washers much more often. Remove the stem again and take a look inside at the seat. Replace it using the tool if it looks at all rough, which I suspect will be the case.

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  • Hi J... It looked smooth, used the proper tool last time, washer isn't visibly torn/worn just crushed/seems not to "rebound", like the wrong combination of pliable and rigid. Is there another type of washer that will work without increasing failure rate? How often would one expect to replace a brass seat that mates to rubber? Should I resign to replacing the seat every 2-3 years? This seems odd. I haven't heard of others having to do this... THANKS! +1. I'll prob get some seats, but I know we've tried alternate washers in the past... can't remember what kinds though. Also updating Q.
    – NOTjust -- user4304
    Commented Jun 8, 2018 at 22:31
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    Adding just a note to the above suggestions, I've noticed if the leak has gone on for a while, the brass seat will either have a buildup of scale or film, and have even had it erode a tiny etching in the brass . . . being a DIY'r I thought about cleaning up the brass seats, even polishing them, and re-using, but they are so cheap, I just buy new ones and add the old brass to my recycle bin . . . and mine only seem to last 3 to 5 years . . . it may be due to the very hard water we have here.
    – user135215
    Commented May 16, 2021 at 18:02

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