The 8" Hersey model 2 is a Double Check Valve that was produced from 1975 to 2004. It has a cast iron body. From 1977-1993 the cast iron bodies were galvanized coated. From 1992-1993 the HP painted epoxy was available as an option to the galvanizing. In 1993 a fused epoxy coating became the standard. In 1988 the device lay length changed. The earlier model being 5/8" shorter. Despite the change, repair kits remain the same. Check seats are removable but a seat removal tool is needed. in 1993, the check cover design was changed. Early models used a cover gasket and after the change, a cover O-Ring was used. Hard parts are no longer available and only rubber repair parts are available.