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Thread: GROHE - Thermostatic Valve Layout - help?

  1. #1
    DIY Junior Member LesMan's Avatar
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    Default GROHE - Thermostatic Valve Layout - help?

    I purchased a house that has a shower with multiple shower heads... and not enough flow.

    Recently - I decided to upgrade the hardware, and purchased a GROHE Thermostatic Mixing Valve (with 11gpm at 45psi)... along with (3) Volume Control Valves for the various shower heads. I'm hoping this will give me the "shower experience" I am seeking (lots of water / pressure.)

    I'm reading the Thermostat Mixer instructions... and it says that a SHUTOFF DEVICE must be installed after the mixed water outlet.

    I'm assuming that these VOLUME Control Valves will function as a Shutoff Valve... is that correct??

    OR - do I have to buy / install an additional SHUTOFF Valve??

    Thanks,

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    The volume controls should work. If the supply lines aren't 3/4", a larger valve may not make much difference. What is the water pressure? If you have a PRV, you might try raising the pressure a little. Note that the flows listed are for a specific input pressure, if you pressure is low, you won't get that flow.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Junior Member LesMan's Avatar
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    Default Should work... or WILL work??

    I measured pressure at the shower head... and I currently have 75psi.
    There appears to be plenty of pressure.

    So - before I start cutting and soldering... The Volume Control Valves that I am going to use SHOULD WORK or WILL WORK as the required "Shut-off Valves"??

    I don't want to put all of this together and then find out that "even though it should have worked" that it actually doesn't - and I have to take it all apart and start over.

    ANOTHER QUESTION ... if I have 75psi at the highest point in my house... why is it that when the clothes washing machine is running, the shower is just at a trickle??

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default valves

    That is the function of the control valves, to turn the water on and off to the various items. Otherwise you would have used a valve with an off feature and a diverter fitting to operate the devices you wanted.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    People confuse pressure and volume. A soda straw sized pipe and a fire hose with the same pressure still has the same pressure, but you'll get a lot more volume out of the fire hose. Sounds like you don't have enough volume. This could be because of undersized pipes, meter, supply line, or old pipes that have corroded, or just poor design (too small distribution lines in the house).

    Do you have any old galvanized supply pipes, either from the street or in the house? Might be time for a repipe.

    Run a test...get a bucket and put it under the tub filler. Run it for a minute, then measure how much water you actually got out of the spout.
    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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