These check valve assemblies are used inside Pro-Series skimmers to bring the flow of water from the pump up to the outlet hole in the back wall of the skimmer. In an ideal world all pumps would have their outlet at the same height but that is not the case so various height assemblies are needed. Each assembly includes a check valve which keeps the plumbing line full of water even when the pump is off. Please see chart below for the correct pump/skimmer check valve.
CVA20TH is for TH series pumps in PSA5000, PSA7000, PS1V or PS1FB skimmers and JAFM, JAFL or PV60E vaults