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Thread: Backwater valve installation question

  1. #1
    DIY Junior Member darren_t_johnson's Avatar
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    Apr 2013
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    Default Backwater valve installation question

    Hi,
    I'm going to be installing a Mainline backwater valve, and the instructions say I need at least 2% grade.

    I over analyze things... so does that mean the inlet pipe and outlet pipe have to have at least 2% grade, and the backwate valve should be level? The outlet pipe is already 3/4" lower then the inlet pipe.

    Or should the backwater valve itself be installed on a slope? This doesn't sound right to because it the unit is slopped too much, the flap might not close properly.

    Has anyone installed one before and/or offer advice?

    Thanks
    Darren

  2. #2
    Moderator & Master Plumber hj's Avatar
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    Default

    2% is the STANDARD minimum slope for a properly installed drain line. Your problem, if anything is that the inlet and outlet are 3/4' lower which creates a problem in a "straight pipe". Unless you can excavate enough pipe to make up that 3/4", you will have to install the BWV with a "backwards tilt" to make it fit.
    Licensed residential and commercial plumber

  3. #3
    DIY Junior Member darren_t_johnson's Avatar
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    Default

    Hi hj,
    yes, 2% is the "1/4inch per foot" minimum that is required. I'm digging up a lot, and have more then enough room to make up that 3/4" difference.

    My main concern was that should the Mainline backwater valve unit itself be level, and the inlet and outlet pipes should have the 2% minimum grade.
    Or is the backwater value supposed be tilted so that the 2% grade is consistent across the valve unit. The instructions for the valve are vague about this, and I haven't gotten any feedback from the Mainline website.

    NEVERMIND.

    I was just typing my response and realized that the 3/4" difference is more than the required 2% grade... for some reason I thought it was not.... so the 2% grade minimum is referring to the inlet and outlet pipe.

    sometimes it helps to talk/type it out...

    Thanks, and sorry for posting a pointless question.

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