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Old 29-04-2017, 23:07   #91
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Re: Bilge Pump Non-Return Valve

It actually doesn't matter how long the pump runs, they have to suck air before the bilge is dry. Let's talk about the typical submersible pump. The pump will have a strainer base to keep debris from getting into the pump intake. This base holds the pump intake up off the bilge floor so that water can get into it. The higher capacity the pump, the bigger this gap has to be. Typically it might be half an inch. Once the water level drops to half an inch, it doesn't matter how long the pump runs, you're going to still have a half inch of water in the bilge. On top of that, you'll get the flow back from the hose when the pump stops.

If you use a positive displacement pump, like a diaphragm pump, you can reduce this left over water. You will give up capacity in an emergency and you'll still have some residual water.
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Old 30-04-2017, 09:15   #92
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Re: Bilge Pump Non-Return Valve

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Originally Posted by HopCar View Post
It actually doesn't matter how long the pump runs, they have to suck air before the bilge is dry.
It doesn't alter the fact that my bilge is much drier if I hold the switch in "manual" for about 30 seconds after the automatic float switch has turned off. Most of this time the pump is slurping a mix of air and water, but a significant amount of water still gets expelled ... and this is enough to prevent the pump from cycling in a swell.
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