The 4" Wilkins 375ADA Reduced Pressure Detector Assembly began production in 2004 and is still currently in production. The 375ADA uses grooved fittings between the backflow and valves. Epoxy coated cast iron body has a single victaulic style cover houses both plastic cam checks and a plunger style bronze relief valve hangs below. An external sensing line pressurizes the diaphragm. Self contained cam checks are held in place by plastic retaining rings. Use caution when servicing as retainer rings often snap. Bypass valve shall be 3/4" 975XLD. No special tools are required for servicing.