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Holding tank pumpout question

Discussion in 'Technical Discussion' started by TahoeJohn, Aug 12, 2021.

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  1. TahoeJohn

    TahoeJohn Member

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    Hi, I've been spending some time refreshing the holding tank on our Horizon 76 MY, including a complete pump out, new dip tubes, new SCAD monitor, etc.

    As purchased, the setup looked something like this:
    pumpout.jpg

    The lettered devices are check valves. The output flapper on the pump ("B") was rotted and nearly completely missing. And the vent check valve ("D") was inoperative (allowing two-way flow). I purchased a rebuild kit for the pump, so it's working again, and have replaced "D" with new. (My guess is that the previous owner added "C" to compensate for "B" being broken.)

    To my question: Are check valves "C" and/or "E" a good idea or are they just adding unnecessary restrictions to the path overboard?

    Thanks!
  2. Rusty Mayes

    Rusty Mayes Member

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    A good argument could probably be made for either case. If I were to remove one, I would think E is really safety back up in case the thru hull was stuck open. C is certainly redundant as well. I think the system would work with both of them removed and eliminate MX issues over time.
  3. Pascal

    Pascal Senior Member

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    First of all what kind of pump do you have ?

    you don’t need check valves in the system, I don’t think I v ever seen any. The vented loop at the top is there to prevent any syphoning back into the tank.
  4. TahoeJohn

    TahoeJohn Member

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    The pump is a Jabsco diaphragm-style with integrated check valves.

    Jabsco_59090_series.jpg

    Sounds like I can remove those two extra check valves and improve the pumpout rate.

    Thanks both!
  5. Pascal

    Pascal Senior Member

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    That’s not a diaphragm pump but a bellows pump with duckbills on each end which act as check valves. No reason to have these check valves in the discharge line
  6. TahoeJohn

    TahoeJohn Member

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    Great, thanks. And now I know what to call that pump. : )
  7. BRyachts

    BRyachts Member

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    I would leave "E" in place, just a good safety in case of a ruptured hose. Without it discharge line will seek sea level equilibrium. "C"can go away.
  8. Capt J

    Capt J Senior Member

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    I agree also
  9. Pascal

    Pascal Senior Member

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    It doesn’t matter if there is sea water in the hose between the sea cock and sea level as long as vented loop is high enough. I don’t see the point of adding a valve plus 4 extra clamps below waterline. I have never seen a check valve on the discharge hose on any boat I v owned or run