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Thread: Max Water Pressure from a gravity fed water tank

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  1. #1
    DIY Junior Member abc's Avatar
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    Default Max Water Pressure from a gravity fed water tank

    I have a water tank on the roof to gravity-feed the house. Will I get more pressure coming out of the tank with a 2" line mounted on the side wall of the tank (at the bottom), or a 2" line mounted on the bottom surface of the tank in the middle?

    Thanks
    Paul
    Last edited by Terry; 11-19-2012 at 05:11 PM.

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    DIYer, not in the trades LLigetfa's Avatar
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    The only way to get more pressure is to raise the water level.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Don't confuse volume with pressure. The larger the pipe, the more volume you can get, but it will have no impact on pressure. If you try to get more volume than a pipe can supply, all outlets will slow down. This is where larger pipes or higher pressure make a difference.

    Taking a shower with a gravity fed supply can be less than thrilling...there, you need a pump or height to increase the pressure.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Test, Don't Guess! cacher_chick's Avatar
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    If your water level is 15 feet above grade, you will have 6.5 psi. This will work for showering if you have a lot of volume. It will not work well using one of today's regulated shower heads.

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    DIYer, not in the trades LLigetfa's Avatar
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    Ja, but the showerhead is not likely to be at grade. If the showerhead is 7.5 feet above grade the pressure will be 3.25 PSI.

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    Test, Don't Guess! cacher_chick's Avatar
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    Quote Originally Posted by LLigetfa View Post
    Ja, but the showerhead is not likely to be at grade. If the showerhead is 7.5 feet above grade the pressure will be 3.25 PSI.
    Very true.
    This may very well be much of the reason people did not commonly have showers in their homes 100 years ago.

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    DIY Junior Member abc's Avatar
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    Default Gravity Fed System

    If the tank on the roof has sufficient venting at it's top, are additional air vent tubes necessary at various points in the sytem?

    Paul

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    No need for additional vents in the supply system...not to be confused with vents for the drainage system which is totally separate.
    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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    You probably have an "open tank" system, so there is no need for vents of any kind. The pressure delivered to the toilet, shower, or sink depends on how high the "top of the water" is from the fixture. The lower the faucet, the more pressure you will have. A shower head, because it is "high" above the floor will be closer to the "water level" and thus have less pressure. It has NOTHING to do with the pipe sizes.
    Licensed residential and commercial plumber

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