Low *Tub Spout* Flow with All New Plumbing

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Borisj

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I just built a guest house myself. Everything is new, including pipes. With no cartridge installed, and the stops open far as they go (~½” of threads showing), I get ~8 GPM flow out of the Delta rough-in valve body (R10000-UNWS).

I’ve tried 3 cartridges (w/3/4" x 12" L brass nipple from valve body to spout drop-ear) and all badly reduce flow from the tub spout (i.e. showerhead flow restrictors are irrelevant here). #1 (RP46463) reduces it to 1.9 GPM. #2 (same model) reduces it to 2.3 GPM. #3 (RP47201, higher flow) reduces it to ~3.4 GPM. I’ve never installed a Delta cartridge before, but it seems straightforward, what could I be missing?
 
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GrumpyPlumber

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Showers are supposed to be 2.5 gpm max by fed guideline (water saving), tubs a little more, running water through the open chassis of a shower valve is not what you can expect from the actual valve.
 

Reach4

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I’ve tried 3 cartridges and all badly reduce flow from the tub spout (i.e. showerhead flow restrictors are irrelevant here). #1 (RP46463) reduces it to 1.9 GPM. #2 (same model) reduces it to 2.3 GPM. #3 (RP47201, higher flow) reduces it to ~3.4 GPM. I’ve never installed a Delta cartridge before, but it seems straightforward, what could I be missing?
How many gpm for all-cold and for medium? I am wondering if there is some temperature thing, or maybe a path size thing.
 

Borisj

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Showers are supposed to be 2.5 gpm max by fed guideline (water saving), tubs a little more, running water through the open chassis of a shower valve is not what you can expect from the actual valve.

I know, letting water run through the open chassis, was an experiment to prove that the plumbing before the chassis/rough-in is not the problem. When I put the cartridge in, I do not get anywhere near the stated flow rate for the *tub*... which is not affected by the 2.5 GPM restriction. Either way, the shower doesn't hit its rating either (tops out at 1.3 GPM).

How many gpm for all-cold and for medium? I am wondering if there is some temperature thing, or maybe a path size thing.

All my measurements are all-cold. Path size can't be the problem - the shower/tub is the first thing in line, and the fixtures later in the line have their expected/rated max flow (e.g. the washer shutoff set).
 

Reach4

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If the path thru the valve inputs limits you, then medium may flow more GPM thru the tub spout.

I did not intend to imply that I had knowledge of those cartridges, but I only proposed an experiment.
 

GrumpyPlumber

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You may have gotten flux or sediment in the cartridge, soak in vinegar, let it sit, then shake it the vinegar.

If this happens to be a Jacuzzi valve, that's a known issue.
 

Borisj

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You may have gotten flux or sediment in the cartridge, soak in vinegar, let it sit, then shake it the vinegar.

If this happens to be a Jacuzzi valve, that's a known issue.
The cartridge is totally clean and brand new. And it wasn't installed when I piped. Personally I would never solder near a cartridge. In this case, the tub spout outlet of the mixing valve goes 1/2" MPT (on cartridge) -> 1/2" to 3/4" FPT brass coupler -> 3/4" FPT brass nipple to tub spout drop ear. It's a Delta valve.
 
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