NDS 1795C20 Clear 2 in True Union Spring Check ValvePrevents backflow and helps hold prime in pool or spa plumbing; Flo Control 1795C20 is a clear, compact true union spring check valve for 2" slip lines. It uses a 5 lb spring and a see through PVC body so you can verify operation at a glance. Union ends let you pull the body for cleaning or replacement without cutting pipe, with EPDM seals for chemical resistance.