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Thread: 3/4 to 1/2 valve/pipe for shower head

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    DIY Junior Member tomdiy's Avatar
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    Default 3/4 to 1/2 valve/pipe for shower head

    Shower installation with two shower heads each on its own volume valve. The supply into the kohler themostatic valve is 3/4 pex into 3/4 cooper into the valve, exiting the valve is 3/4 copper reduced to 1/2 copper then into each of the 1/2 volume valve and 1/2 copper out to the shower heads, both shower heads seem light on flow both hot and cold (Other fixtures on same feed are fine), Kohler says I should have keep it all 3/4 after the valve but don't most shower heads have to reduce to 1/2 at some point? I was going to replace the valve cartridge to see if it helped but figured I would ask for thoughts before spending the money. Thanks in advance

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Unless you removed the restrictor (some can be easily, some can't), each shower head is mandated to have a max of 2.5gpm. But, 1/2" pex might be hard pressed to provide 5gpm. The ID of pex is considerably smaller than that of copper in the same 'size' (which is the OD, not the ID). This is because copper is much stronger, so it can be thinner than pex. What's strange to some is that 1/2" copper is unlikely to be 1/2" ID and it is 5/8" OD, although it is much closer to 1/2" than pex.
    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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    Moderator & Master Plumber hj's Avatar
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    quote; What's strange to some is that 1/2" copper is unlikely to be 1/2" ID and it is 5/8" OD

    The i.d. is determined by the tubing's wall thickness. Type "K" with the thickest wall is ALMOST 1/2" i.d., about 1/40" larger than actual 1/2".
    Licensed residential and commercial plumber

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    DIY Junior Member tomdiy's Avatar
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    Thanks, I guess I was not clear, the flow I am getting is less than I have from predominately 1/2 inch in the other bathrooms, why would 3/4 supply reduced to 1/2 for the last 10 feet of the run after a valve reduce the flow to less than a run which is mostly 1/2 inch

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Few valves' internal passages are the same diameter as the supply pipes. IF the pipe supplying and outlet of the valve are both the same size, the flow rate increases in the valve and it doesn't act like a restrictor much (the venture effect). If the outlet pipe is smaller, it stays slowed down and the valve is a real restriction to flow. The outlet of a faucet goes through the spout, which is usually unrestricted (well, it may have an aerator on it).
    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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