Series 900 Reduced Pressure Zone Assemblies were produced from approximately 1970-1988. The device was available in sizes from 3/4 - 6". Smaller 3/4 - 2" 900's must be removed from the line for service. The device featured in-line checks and replaceable seats. Limited parts are still available for the 900 Series. Some specialty tools are required for servicing, but are usually provided with approved repair kit.