Non-Return Valve Problem

[SAFRAN]

Hi out there. I have a question concerning a non return valve for my air condition. The salt water inntake is aft. This is fitted with a filter and connected via a hose to a pump. the pump is connected to the air condition unit with a non return valve in the middle. What i suspect is that when i sail or run by motor the speed of the boat may FORCE water into the salt water intake valve, bypassing the pump and the non return valve and somehow exit into the boat. Is there anybody out there with knowledge of this theory? Thanks

SAFRAN