Backflow Preventer. Overview Backflow Preventers-Dual Check for Domestic water Features Dual Check Valves may be installed in either a vertical or horizontal position and should be installed immediately down stream of the water meter. Product Specifications Application Backflow Preventer Dimensions (in.) 4 3/8 in. long x 2 1/8 in. wide Dimensions (mm) 111 mm long x 54 mm wide Maximum Safe Operating Pressure (psi) 150 psi Maximum Safe Operating Pressure (kPa) 1034 kPa Weight (lb) 1.0 lb Weight (kg) 0.45 kg Approvals, Canadian Standards Association Certified Ambient Temperature Range (F) 180 F Maximum Ambient Temperature Range (C) 82 C Maximum Connection Size (in.) 3/4 in. Approvals, Others ASSE Certified Connection Type NPT Pipe Size (inch) 3/4 in. Pipe Size (DN) DN20