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post #6 of Old 11-11-2012
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Re: Bilge pump non return valve.

Originally Posted by Maine Sail View Post
These valves quite often stick shut especially if the bilge pump does not cycle often. The biggest draw back is the added head pressure that the pump can not overcome. This additional head is caused by the standing water in the discharge hose, and thus, a centrifugal pump will simply cavitate and do nothing but make some neat little bubbles in the bilge.

For boats stored in-water during cold weather the water in the bilge hose above bilge level can freeze when the bilge water is not frozen. This present an impossible situation to pump into.

Fill a grain silo with corn and then try to push a door open into it...... Pretty tough. The check valve creates the same type of resistance to the bilge pump, Centrifugal pumps deal horribly with any added head pressure..

Check valves on rotary vane pumps or diaphragm pumps do not suffer the issues they do on centrifugal Rule style pumps. I have seen everything from ruined interior cabinetry, cabin soles and engines due to stuck check valves. I have also seen boats that sank because of a stuck check valve..

The largest maker of centrifugal bilge pumps, Rule, specifically recommends not to use them.

They can be a danger if used on a system with centrifugal bilge pump. Bilge pumps are safety items anything that can prevent the pump from pumping becomes a potential danger.
Maine, there are instances where you might need to install a check valve (I needed to) and ways to do so that doesn't give rise to the "standing water in the discharge hose" you mention (install it high up near the discharge point - not in the bilge with the pump itself).. I guess exactly what you do depends on the specific circumstances and the type of boat.

I've known check valves to fail open (bits of rubbish preventing the flap closing), but I've never heard of one sticking closed.. but then we don't get the freezing weather you get. I've known of boats that sank because there was no check valve fitted when they needed one..

IMHO, the bottom line is: Don't install a check valve unless your particular installation means you have no other alternative.

BTW, the other thing that can prevent the pump pumping is lack of a strum box.. make sure you use one.

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