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Thread: surge tank inlet

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    surge tank inlet

    On a surge tank inlet from a negative edge gutter what are the ramifications of the entering from the bottom of the tank. Inlet pipe 6", min gradient 1/4" per ft, max flow 120 gpm, water in transit 100 gal, tank below gutter out let, all flow regulators properly in place. I have read that the inlet should be as high in the tank as possible, but water seeks its own level and I can not see the problem of putting the inlet at any level.

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    Patrick_B's Avatar
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    Re: surge tank inlet

    Welcome to TFP!

    Why not just put it higher if that's recommended best practice?
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    JasonLion's Avatar
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    Re: surge tank inlet

    Welcome to TFP!

    You want to prevent water from flowing backwards from the surge tank back to the gutter/trough. This is typically done by providing an air gap between the water in the surge tank and the inlet pipe (i.e. inlet high on the side of tank). It is also possible to get the same effect with a check valve, though that is just slightly less reliable, as check valves can get stuck open.

    There are also dynamic flow rate issues. It is not sufficient for the water level to be setup correctly, you also need to take into account the relative flow rates of the different parts of the system at different times. With a bottom mounted inlet, the pump could draw down the surge tank more quickly than water could flow in from the trough for a short period, even if the average flow rate from the trough was higher than the pump flow rate. This could potentially cause the pump to lose prime.
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    Re: surge tank inlet

    Quote Originally Posted by Patrick_B View Post
    Welcome to TFP!

    Why not just put it higher if that's recommended best practice?
    Constants on placement of the surge tank and concealment of the 6" feed pipe might require water to enter the tank from a lower level. Trying to avoid burying the the tank and putting it in a subterranean existing equipment room.

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    Re: surge tank inlet

    I have no means to calculate the actual flow to the tank from the gutter, but with a 6" pipe with 1/4" pitch it should be in excess of 300 gpm. I know that the question is contrary to convention. Just trying to understand the science of it. All other parts of the system are to spec. but the tank has twice the the capacity for bather surge. I]n such an installation the lower 75 percent of the feed pipe(25'ft) would be filled with water at all times essentially making it part of the surge tank. I take that as a bonus, but the science may disagree.

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    JasonLion's Avatar
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    Re: surge tank inlet

    The key thing is that the pump should never be able to run the surge tank dry. A lot of details that we haven't discussed yet enter into that consideration. Having an air gap on the inlet pipe is one common way to help guarantee that without having to do a lot of math, but it is not an absolute requirement.

    These systems tend to be complex to design from scratch. It is best if you work with an engineer who is familiar with similar setups.
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