imagine a straw. You are inhaling air into it and when u stick it into a cup of soda, wut happens? YOu start sucking the soda through the straw right? Now cut a hole in the straw and try to suck up the soda through a straw. Nothing comes up but you seem to keep on sucking up more air, right? That is the idea of a bypass valve. It lets the intake take in air from mid pipe so you don't end up sucking water into the engine causeing hella damage. So if ur intake is completely submerged, the bypass valve opens so ur engine will be able to breath insted of drown.