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Almost all diaphragm pumps work as pass through pumps, because they use a joker or check valve at the outlet. If there is any vacuum on the outlet side, the water will push through. However, water can't flow back through the pump... so yes, a diaphragm pump will act as a check valve... because that is effectively how it works... it is two check valves with a bellows between them. Open the bellows, the outlet hose valve closes and water fills it...compress the bellows, the inlet side closes and the water rushes out the outlet valve...
What they should have done is put the Whale Gusher in the line going to the seacock and through-hull discharge, not in the common line coming up from the holding tank pumpout fitting. That way, if you have the y-valve pointed to the deck fill, you can pour water in via the deck fill.
I would highly recommend that you make this change ASAP... It will make your life easier and it will put less wear and tear on the pump itself.
So the setup should end up like this
Tank pump out fitting ====> y-diverter =====> to deck pumpout fitting
...............................................val ve =====> Whale Gusher Pump ====> seacock/through-hull.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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Last edited by sailingdog; 10-26-2008 at 02:36 PM.