These are in a set which includes flange adapters and support rings. (except of 131319) Fitvalf Pvc Spring Check Valve O-rings EPDM. IMPORTANT INFORMATION: * Arrow mark indicates fluid flow. * For horizontal installation, be sure that the arrow mark is on the top. * This valve works automatically to prevent reverse flow. Backflow can cause flooding or make damage to the system. It is easy to install and requires the use of solvent cement. Operating pressure for our 63MM - 110MM U-PVC Swing Check Valves is PN16. U-PVC Swing Check Valve Usage Areas : ♦ Water and Waste Water Treatment ♦ Swimming Pools and Water Parks