Caleffi 519709A Bypass Differential Pressure Valve, 1-1/4 in Nominal, FNPT x C End Style, 150 psi Pressure, 45 gpm Flow Rate, Brass Body

The differential pressure by-pass valve is used in systems with a fixed speed circulating pump supplying several zones controlled by two way zone valves. This valve ensures that the head pressure of the pump is proportional to the number of two way valves being closed. It will bypass the differential pressure created by the pump as the zone valves close, thus eliminating water hammer noise.