Pentair R172221 Vent Valve O-Ring Replacement Pool/Spa Filter and Feeder Vent valve o-ring replacement Fits Pentair Dynamic series I, II RTL/RCF, III RTL/RCF inline pool/spa cartridge filter models RDC-25, RDC-25S, RDC-50, RDC-50S Also fits Pentair Rainbow high capacity automatic chlorine/bromine pool and spa feeder models HC-3315, HC-3330, HC-3340 Also compatible with Pentair Dynamic RCF-RTL series cartridge filter chlorine/bromine dispensers