The AWWA C509 design standard was developed based on the physical characteristics of cast iron while AWWA C515 was developed based on the more robust physical characteristics of ductile iron. AWWA C509 standard was developed in 1980 to formalize the design standard for resilient seat valves for water and waste water. The wall thickness was adopted from the standard first published in 1952 for metal seated valves – AWWA C500. The wall thickness in C500 was, in turn, adopted from the original gate valve standard created in 1913 for cast iron valves with the wall thickness design based on the metallurgy of cast iron. The greater strength and durability of ductile iron allowed for the development of a valve design with reduced wall thickness while maintaining at least the same or greater resistance to internal working pressure with the added benefit of greater resistance to mechanical damage from transportation and handling.