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Thread: Back Flow Preventer

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    Back Flow Preventer

    Is it advisable to put a back flow prevented on the input side of a pump.. that way it would prime easier and quicker...

    The thought just popped into my head... I'm dangerous like that!
    Escondido Ca [*]~23000 gallon plaster pool built in the 70's[*]Pentair VF Pump running 10hrs at 1800rpm getting and estimated 35-40 GPM thruput[*]Sta-Rite Cartridge filter

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    Mod Squad jblizzle's Avatar
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    Re: Back Flow Preventer

    Interestingly, doing so can actually be dangerous ... by making more of an entrapment risk.

    Unless your pump is well above your pool water level, the pump should have no problem priming.
    Jason, TFP Moderator
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    Re: Back Flow Preventer

    I was just wondering and thinking.. things get dangerous when I start thinking

    explain..
    an entrapment risk
    Escondido Ca [*]~23000 gallon plaster pool built in the 70's[*]Pentair VF Pump running 10hrs at 1800rpm getting and estimated 35-40 GPM thruput[*]Sta-Rite Cartridge filter

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    Mod Squad jblizzle's Avatar
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    Re: Back Flow Preventer

    With pump running, a person could get held against the drain underwater. If you turn off the pump, the check valve would prevent them from being released.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Re: Back Flow Preventer

    I put a Jandy check valve prior to my pump due to the height above the water surface, although it's a minor distance I think would prime just fine anyway and you just scared me

    However, it's an assumption everyone would have more than one suction side source, with two skimmers and one main drain that tie together prior to the check valve wouldn't the vacuum from the main drain just equalize drawing water from the skimmer line?

    Sorry to hijack, but seemed related
    Scott
    15,000 Gallons vinyl in-ground screen enclosed, Hayward Eco-star SP3400VSP, Hayward Aqua Logic PL-Plus, Hayward T-15 Salt Cell, Hayward S244T Sand Filter, Polaris 380 with booster pump, Hayward heat pump HP50HA. K-2006 kit.

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    Mod Squad jblizzle's Avatar
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    Re: Back Flow Preventer

    Yes it would only be an entrapment risk if suction was isolated to one source of water before the pump.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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    Re: Back Flow Preventer

    Quote Originally Posted by jblizzle View Post
    With pump running, a person could get held against the drain underwater. If you turn off the pump, the check valve would prevent them from being released.
    I know you and I have discussed this at least once, and I'm not attempting to be argumentative, just looking to further the discussion. I've seen it stated by others, and maybe you also, that if you have to put a check valve in that you should put it on the discharge side of the pump. With my set up I was having trouble priming because their is an o-ring leaking on the handle of my top mount multi port valve, so a check valve after the pump would've solved my problem. I didn't know where the leak was at the time, and I was just trying to keep the pump from burning up. What's the difference in having a check valve before or after the pump as far as entrapment risk? It's still going to prevent flow backwards either way. Either I misunderstood something, or there is an assumption that if it was after the pump you could pop the lid to relieve any vacuum in such a situation that someone was entrapped. I have two skimmers plumbed individually and a dual main drain. All three tie into a single manifold that goes to the pump. My check valve is after all the lines tie together on the main manifold, about a foot before the pump inlet. I could see where if I was pulling only from the main drains, and one main drain was completely plugged somehow, that the single remaining main drain could now potentially pose an entrapment risk because taking the pump lid off wouldn't relieve a vacuum with the check valve before the pump. If everything was open, pulling from both skimmers and the main drains like it always is, I don't see how there could be an entrapment risk because any vacuum would be relieved by the open skimmers. Like I said, I'm not trying to be argumentative. I am trying to understand the logic and see if it's something I should look at changing. When I was about seven I got stuck to a huge public pool main drain in 12ft of water. I was scared of pool drains for years, and am still leary anywhere other than my own pool. I have four children, so the first thing I did when we bought the house last year was put the pump pulling from only the main drains, I laid on one drain and felt around the other one to see what kind of suction it had. The drain cover design is such that I could feel no discernible flow to cause an entrapment. I suppose every plumbing scenario would/could be different in this aspect. Have I missed something or is it just a theoretical increase in risk that would only happen in a series of unfortunate events? I suppose most accidents take place because of such a series of unfortunate events.


    30K gallon IG vinyl. 1.5HP 2-speed Waterway Mustang pump. 600 lb sand filter. Polaris 280. Circupool SI-60+. TF-100

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    Re: Back Flow Preventer

    Quote Originally Posted by jblizzle View Post
    Yes it would only be an entrapment risk if suction was isolated to one source of water before the pump.
    Looks like you replied while I was typing my novel.


    30K gallon IG vinyl. 1.5HP 2-speed Waterway Mustang pump. 600 lb sand filter. Polaris 280. Circupool SI-60+. TF-100

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    Mod Squad jblizzle's Avatar
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    Re: Back Flow Preventer

    With modern designs ... the risk is VERY low ... as it appears you experimented with.
    For this to really be a problem, you would need to have a single floor drain (which I do) and have the suction isolated to only that drain (which I don't).

    In addition to the entrapment risk (admittedly low), having a check valve on the suction line is just another place for a suction air leak to develop.
    IMO, except for extreme cases where the pump is many many feet above the pool water level, there should be no need for check valve because the pump should have no problem getting primed and the pump should not lose prime except in the rare times when you open the system (to clean the pump basket or filter).
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

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