The 8" Wilkins 975 Reduced Pressure Zone backflow preventer was introduced in 1990 and was discontinued in 2004. The body was constructed of fused epoxy coated cast iron with a bronze bodied relief valve. Check assemblies were poppet style with self contained springs. Check seats were bronze construction and replaceable. Relief valve is a modular style with a self contained spring. Stainless steel relief seat threads into the body and is replaceable. An external sensing line pressurizes the relief valve. No special tools are required for servicing.