Originally Posted by Maine Sail
... Centrifugal pumps often just make neat little bubbles and the water remains in the bilge...
I experimented a bit with a check valve (NOT on a boat, actually, long story...). My experience was exactly what you describe, it got stuck in the 'closed' state at the drop of a hat.
BUT: I had never thought of doing what Hartley suggests:
"install it high up near the discharge point - not in the bilge with the pump itself"
In that case, you do NOT have the water column keeping the valve stuck in closed. That seems to me the smart way to do it (why didn't I think of that?).
Next time I have a chance, I will try that on my installation.