The 8" Watts 909 Series Reduced Pressure Zone Assemblies were manufactured from 1979 and are still currently in production. The 8" 909 is a cast iron bodied device. In 1989 the 909M1 replaced the original 909. The difference was the relief valve body changed. The relief valve bottom plug was also redesigned and the rv diaphragm was resized. Many devices were not tagged with the "M1" suffix. To be sure which model you have, you must measure the relief valve cover. The original 909 relief valve cover will have a diameter of 12" while the 909M1 will measure 9-3/4". Check valves are self contained and the relief valve is a stem type. In 2010, the LF909 was introduced to comply with the new "Lead Free" laws. All repair parts were converted to lead free in 2013. Lead free repair parts will fit both regular 909 and lead free LF909 models. All 909 models have replaceable seats and require no special tools for repair. Maintenance ManualSpecification Sheet