View Full Version : Shower diverter pops up by itself. Also, a bonus physics/pressure question.

07-10-2012, 09:33 PM
A pretty big plumbing outfit installed my tub/shower. The valve is an American Standard "Central Thermostat with Volume Control". A twin ell feeds the tub/shower. I attached some pics. The problem is that the shower diverter on the tub spout will pop up all by itself after a minute or so, especially when the flow/volume is turned about half-way or more. Otherwise, the diverter does its job, with no leaks in either up/down mode.

After reading through your forum, it seems like a pressure problem is at work, but I could use some advice. The plumbing company has already come out once and replaced the tub spout/diverter. Actually they replaced it twice… first with a temporary unit (totally different style) that actually worked perfectly. Then, with a proper replacement, which seemed to work, but maybe wasn't tested long enough, because the same symptom returned. The plumbers were dumbfounded at the initial problem, and apparently so was the American Standard tech they called, so I'd appreciate any advice to pass along before I contact the plumbers again. (I got the feeling these plumbers spend most of their time doing commercial work and hospital/lab stuff, not residential.)

Clue#1: Initially there was a pressure problem to the shower that the plumbers tried to explain away as a shower head design. Ultimately I took it apart myself and found blue stuff (pipe dope or shredded T tape?) plugging the restrictor in the shower head. After cleaning it the shower pressure seemed adequate. I think this might be a clue because: Where did that stuff come from?

Clue#2: My pics might show reducers at all three valve connections, (although I don't exactly know what they look like.) If so, maybe the plumbers had to adapt 1/2" copper pipes to a valve with 3/4" connectors? The valve comes in both 1/2 and 3/4 inch versions. I specified the 1/2" version, but I never verified which part they actually provided.

Clue#3: I took off the shower head and noticed that when I put my finger on the hole, the water pressure to the tub drops nearly in half. When I take my finger off, it immediately surges to the tub again. With the shower head off, I managed to trigger the ghostly diverter by covering the hole about 75% (but strangely not at 0% or 100%). I can hear/feel the hole sucking a lot of air. Bonus physics question: How does the shower pipe regulate the tub flow? Or in other words, why does water flowing through the tub spout create a vacuum in the shower pipe?

FYI, the walls were all finished before this problem was noticed, so I can't get any new photos.


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07-10-2012, 11:41 PM
Has anyone measured you house water pressure????? Check both static and dynamic

07-11-2012, 07:11 AM
Your description is "illogical" because the diverter is gravity operated so there should be no way for the water to "push" it up, (especially with almost zero back pressure from the water flowing out of the spout), unless there are other dynamics at work there. As for the shower controlling the flow, logically it can't, because the two ONLY merge at the twin elbow. However, since the twin elbow was connected backwards, anything is possible. The way it is installed, you have a small jet of water from the valve flowing past the larger opening which the shower is connected to. This is creating a venturi which will suck air from the shower head, but should not affect the actual flow of water, but could reduce the "apparent" flow which is a mix of air and water.

07-11-2012, 07:43 AM
Has anyone measured you house water pressure?????

No, (not yet). I'm on the town water supply, and in general the house pressure seems the same as every other place I've lived, and the other shower in the house has no problems. However, this tub does seem to fill a little faster than others. Anyway, I'll have the pressure checked. I assume you're thinking it might be too high? Thanks for the quick reply this morning. This site is great.

07-11-2012, 08:36 AM
...the diverter is gravity operated so there should be no way for the water to "push" it up...
Crazy, right?! The diverter handle jiggles while the water is rushing through the spout. As it jiggles, it very slowly rises. After about 30-60 seconds, the handle has risen about 1/8", then it pops all the way up. The bottom of the spout isn't wide open like other tubs I've owned. This has some plastic part with spokes that seem to spread (or slightly aerate?) the water exiting the spout nicely. The part moves up/down with the diverter handle. With the water off, if I push the plastic part vertically up into the spout, it and the handle will actually stay up. (In my limited past experience, tub diverters usually only stay up while water is running.) I also noticed a squishy sound when moving the handle up/down… sounds like a wet rubber seal of some sort, unlike the metal-on-metal sound I'm used to in other tubs. Could this tub spout/diverter be a new (but flawed) design? The current spout model is 8888.022. (I just realized that the original/correct spout was 8888.220… apparently someone goofed when ordering the replacement… I knew something looked different.) I don't know the temporary spout model or even manufacturer… too bad, that one seemed to work, but it didn't match the style at all.

… the twin elbow was connected backwards … This is creating a venturi which will suck air from the shower head.
Ah, that makes sense. But how can you tell the twin elbow is backwards? (American Standard diagram below.) Hmmm… your venturi observation would still apply even if it was connected correctly, right?

Thanks again… this forum is great.


07-11-2012, 10:49 AM
A twin ell needs the two larger openings to connect between the valve and the spout...the smaller one (if they're different) goes to the showerhead.

By code in most places, if the static water pressure in the house exceeds 80psi, you need a pressure reduction valve (PRV) AND an expansion tank.

07-11-2012, 01:54 PM
I have been in homes that needed a replacement pressure reducer. Without adequate flow, the diverter would not stay diverted. Replacing the PRV solved that. It was a pressure issue on that job.

07-11-2012, 04:22 PM
No, if the twin ell is installed correctly the flow from the valve goes directly to the spout, and is NOT a "jet" passing in front of the smaller shower opening. Your problem could also be caused by that concentrated "jet" of water hitting the diverter and its velocity forcing it up. The "front" opening which is for the valve is a larger port and it goes downward and is then dispersed to the spout. The shower opening at the rear points "forward" and since it is also much smaller creates a high velocity jet stream.

07-12-2012, 10:46 AM
Forgive my novice eyes, but it looks like both the diagram and pics show the shower pipe attaches to the back (curved part) of the ell, and the valve connects to the middle port of the ell (after a big loop to get to the top of the valve). The blue side of the valve is facing the tub. Am I seeing it wrong?

07-12-2012, 06:51 PM
I looked at it again. Your novice eyes are fine.