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Sea recovery aquawhisper 1400 sucking air

Discussion in 'Technical Discussion' started by Pascal, Jul 19, 2017.

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  1. Pascal, Jul 19, 2017
    #1
    Pascal

    Pascal Senior Member

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    trying to figure out why our 1400 SR is sucking air, and getting worst getting to the point where it takes 10 minutes of running the feed pump till I can start the high pressure pump. Unit has the glass tube flow gauges and the stream of air bubble is easy to see. When high pressure pump starts, air flow gets worst and eventually purges itself out. Obviously I need to keep the pressure regulator all the way down or the air causes damaging knocking.

    No leaks, clean strainer and thruhull, new feed pump (tech thought the feed pump was the cause, I went along as I didn't mind having a spare)

    I am ASSuming any leak downstream of the feed pump woudl be visible which leave things before the feed pump. If there was a leak there, either at the sea cock, strainer or hose with the pumps off the leak would be visible since it s all below WL

    What am I missing?
  2. AMG, Jul 19, 2017
    #2
    AMG

    AMG YF Moderator

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    I had this issue on an engine once, where the filter in the strainer did not fit right so the lid was not really tight. Easy to check by taking the filter out and try briefly.
  3. 30West, Jul 19, 2017
    #3
    30West

    30West Member

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    An air leak under vacuum needs a much smaller opening than a water leak under small pressure. I put a little dielectric grease (silicone grease made for O-rings and rubber/plastic) on all my seals, gaskets, hoses, it might help. It will definitely extend their life and keep them from sticking to surfaces.
  4. Capt J, Jul 19, 2017
    #4
    Capt J

    Capt J Senior Member

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    It's before the pump. I've had a leak on the suction side of a pump, a few times that did not leak when the unit was not on. It always seemed to happen with joints sealed with plumbers putty or whatever that pliable crap is. I ALWAYS use teflon tape and never have issues with leakage down the road. I would get the pump running and then take a garden hose open nozzle on low and start putting it over seams and fittings and have someone watch and see if the air bubbles disappear. If you get the right spot, it will suck the water in from the garden hose rather than air.
    Last edited: Jul 19, 2017
  5. Pascal, Jul 19, 2017
    #5
    Pascal

    Pascal Senior Member

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    But since it purges itself after a while, I wondering if it's not an issue of the system draining when off. The membranes are high above the pumps, close to the ceiling. I closed the seacock when I last shut down, will see it it makes a difference. I m starting to wonder about the check valve just downstream if the feed pump where the fresh water flush tees in. If that stuck open I wonder if water woudlnt flow back out resulting in a longer time to clear the air
  6. Capt J, Jul 19, 2017
    #6
    Capt J

    Capt J Senior Member

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    It's possible. With remote mounted membranes, I've seen 2 minutes to purge the air......but 10 seems like a very long time.
  7. Pascal, Sep 2, 2017
    #7
    Pascal

    Pascal Senior Member

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    Looks like it was the check valve downstream of the feed pump, just before the tee for the fresh water flush, I opened it up and it had nick on the plastic which apparently was enough for it not close all the way. This cause the system to drain as the membranes are mounted high.

    Now if I could only figure out why the **** thing is so loud... the rack is mounted on rubber isolators but the pump is just loud. You can hear it from further away than the genset...
  8. 101TUG, Sep 2, 2017
    #8
    101TUG

    101TUG Senior Member

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    can be also from pump shaft seal