Theis,

Your concept of placing a vented loop near the centerline of the boat seems like a good idea in either a manual or electric pump. I see no reason why it would not be possible to have both a vented loop and a flapper valve in the lazarette locker, where they would be accessible. It would be a simple matter then to observe just how these devices function under different sea conditions, and to quickly remedy any blockage that might occur in the valve. I would not be enthusiastic about a vented loop in any compartment other than the self-draining lazarette locker.

Perhaps putting a flapper valve in an electric pump line is a different thing than putting one in a manual pump line, but printed material that came with my new Whale Urchin pump has no warnings against flapper valves in the line. The Whale pump and the Guzzler pump that I already have in my boat both have two flapper valves installed by the factory within the bodies of the pumps. The flapper valves that I purchased for my bilge pump lines were manufactured for that specific purpose by a bilge pump manufacturer.

I mentioned earlier that I was able to get one of the two flapper valves in my Guzzler pump to fail by blowing it backwards. I did that by shoving a garden hose on full force into the transom outlet and holding it there. The other valve held however. The valve that failed was not damaged. I was in the process of installing a new diaphragm and valves, so I replaced them anyway. I am keeping the old valves as emergency spares.