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Another sagging vent line

Discussion in 'Marine Plumbing and Sanitation' started by mermike, Mar 25, 2019. Add this thread to a FAQ

  1. mermike

    mermike

    Joined Nov 21, 2012
    27 posts, 4 likes
    Yamaha 33
    US Port Ludlow, WA
    Hi all,

    I think this question was answered, but I would like to confirm. There's no good reason to have a sag (or two) in a freshwater tank vent line, is there? We scrubbed the tank on a new (to us) Y33, and found water and sludge in the vent line. It shouldn't be too hard to straighten out, but thought I'd check before performing surgery.
     

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  2. dlochner

    dlochner

    Joined Jan 11, 2014
    3,439 posts, 1,580 likes
    Sabre 362
    113 US Fair Haven, NY
    There are no good reasons for a sag in the vent line, especially near the tank and there are some good reasons for not having a sag. (same holds true for vents in holding tanks and fuel tanks)

    A low spot in the line will allow water (or fuel or the other stuff) to collect in the line, effectively sealing the vent. Think of the trap under the kitchen or bathroom sink. The trapped water will allow stuff to grow and in the case of the holding tank, plug it up and permeate the hose adding to the smell.

    Water enters the trap because the tank will get over filled or it is filled to capacity and the action of the boat sailing causes some water to get into the vent hose. Or, if the tank is filled with cold water and it warms, the expansion will cause the tank to overflow into the vent.
     


  3. Peggie Hall HeadMistress

    Peggie Hall HeadMistress

    Joined Dec 2, 1997
    7,135 posts, 673 likes
    - -
    US LIttle Rock
    I couldn't have said it better...except maybe to add that it's a good idea to have an ARCH in fuel and water tank vent lines to prevent sea water from contaminating them if/when you're heeled enough to put the vent under water for more than just a brief dip. Holding tank vent lines should be as straight as an arrow...no dips OR arches.
    --Peggie
     


  4. dlochner

    dlochner

    Joined Jan 11, 2014
    3,439 posts, 1,580 likes
    Sabre 362
    113 US Fair Haven, NY
    Thanks Miss Peggie, I've been studying, even spelled your name right. :)

    While I have your attention, what's the hose diameter on a PHII from the pump to the bowl. I forgot to measure it last fall and I want to install a vented loop.
     


  5. mermike

    mermike

    Joined Nov 21, 2012
    27 posts, 4 likes
    Yamaha 33
    US Port Ludlow, WA
    Much appreciated. My partner and I were both scratching our heads trying to figure out why it was done that way. I don't think it's possible to have an arch there without a dip, so we'll make it as straight as possible. I'll let you know if the patient survives ;)
     


  6. Peggie Hall HeadMistress

    Peggie Hall HeadMistress

    Joined Dec 2, 1997
    7,135 posts, 673 likes
    - -
    US LIttle Rock
    3/4", same as the hose from the thru-hull to the pump.
    --Peggie
     


  7. dlochner

    dlochner

    Joined Jan 11, 2014
    3,439 posts, 1,580 likes
    Sabre 362
    113 US Fair Haven, NY
    Thank you.
     




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