aluminum, bronze or stainless steel construction 65, 80, 100 & 150 mm (2.5", 3", 4" & 6") size with fix flow of 75 to 3500 lpm working pressure 6.4 to 12 bar (93 to 175 psi) maximum back pressure as 65% each unit is calibrated and factory tested for flow, induction rate at maximum back pressure .