The 4" Febco 825D Series Reduced Pressure Zone Assemblies was produced from 1988 to 1989. The 825D replaced the original 825, but had a short production run and was in turn replaced by the 825YD. The 825D model changes were a ductile iron body instead of a cast iron body and check assemblies were changed from epoxy coated iron to stainless steel. Check seats were replaceable but are not longer available. The relief valve is a side mount, bronze body with external sensing line. The relief valve body was changed in the newer models and parts do not interchange. A newer relief valve can be retrofitted to the older style device with the conversion kit.