I am considering fitting non return valves to both my cockpit scuppers as on occasions in rough conditions I am getting water flowing back into the cockpit. The cockpit is deep, and about one foot above the water line. A life -raft is fitted in a cockpit :unsure: locker, so I could get salt water flowing around the bottom.

Any reasons NOT to fit this?

Hi John,
Understood.
If the raft is designed to be mounted outside, as so many are, I would suspect it to be fine in a locker that gets wet occasionally.
I believe being pooped, a cockpit filled with water, is pretty rare. I can only think of 2 times that has happened to me and both were partial fillings.
I might consider crossing the hoses, but that would depend (among other variables) on how far outboard the skin fittings are in your design.
If you go with check valves, try the test I suggested before installation. It should not take long and might be interesting.
Let us know what you decide.
My best, Dick