Valve Cross Reference From time to time, older specifications reference a "Dow Figure Number" for certain Resistoflex valves, which prior to 1999, were manufactured and sold by Dow Plastic-Lined Piping Products. This obsolete numbering system refers to the following type of Resistoflex valve: Fig. 373 - Cast Steel Diaphragm Valve with rising stem and travel stop, Class 150. Fig. 573 - Ductile Iron Diaphragm Valve with rising stem and travel stop, Class 150. Fig. 356 - Cast Steel vertical Check Valve, Class 150. Fig. 556 - Ductile Iron vertical Check Valve, Class 150. Fig. 355 - Cast Steel Horizontal Check Valve, Class 150. Fig. 555 - Ductile Iron Horizontal Check Valve, Class 150.