SHV Series Shuttle Valve, Cast Iron, 1/4 NPT Ports, Up To 5.00 GPM & 3000.00 PSI

When pressure hits both inlets, the hardened steel ball inside shifts toward the lower-pressure side and blocks it off. Flow from the higher-pressure inlet gets routed through to the outlet. The two inlets stay isolated from each other the whole time, so there's no crossflow between them. That's the core job of a shuttle valve, and it handles it passively without any external signal or actuation.

With two inlets and one outlet, it routes flow from whichever inlet has the higher pressure over to the outlet while keeping the two inlet flows isolated from one another.