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Thread: Shower Valve Supply Confusion - GPM/Rate of Flow

  1. #1
    DIY Junior Member Erc's Avatar
    Join Date
    Mar 2011
    ATL Georgia

    Default Shower Valve Supply Confusion - GPM/Rate of Flow

    I'm currently in the planning stages of a custom shower. I was looking at the Delta thermostatic valves all of which are supplied by 1/2''. If I couple that with a 3 port 6 setting diverter and given good water pressure, is that 1/2'' line sufficent to run multiple 2.5 GPM outlets? Say a rain shower and a hand shower? And say I run this same setup at the other end of the shower and (hot water aside) occasionally 4 outlets are running at the same time? I have 3/4'' supplies coming to the bathroom currently. Delta doesn't give any GPM or rate of flow info on any of there rough valves that I can find.

    Delta appeared to have better performance reviews on this forum as opposed to Moen and Kohler both of which offer 3/4'' valves.

    Any input is much appreciated?


  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    I wouldn't plan on more than around 5-6 gpm on a 1/2" supply. Some of this is a restriction on the water flow velocity. If your pressure is quite high, you can flow a bit more, but you'll have long term problems as the faster the water flows, it can start to erode the pipe and fittings from cavitation and friction. Most 3/4" valves are capable of about double that flow. Depending on your pressure, you may not be happy with 2- 2.5gpm showerheads...depends on the design. More, is just asking for problems. Few of the valves have full-port openings, so act as a restrictor.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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