The differential bypass valve is used in systems where heating loads may be excluded from the circuit as zone valves close. It controls the excess flow in the system by acting as a bypass while ensuring adequate flow to the remaining open circuits. The differential bypass valve helps reduce velocity noise caused by excess flow through the circuits while maintaining the pump head at a constant value.
The differential by-pass valve should be installed after the pump between the supply and return piping. It can be installed either in the horizontal or vertical position provided it is in accordance with the direction of flow as indicated by the arrow on the valve body.