Darlly 50221 FC 3091 C 5621 PTL25 Spa Pool Filter Cartridge invensys That makes this internal especially That makes this internal especially practical in seats that rely on more intentional stream placement rather than a fixed pattern The Hayward Power Vac vacuum cleaner head is designed for manual pool cleaning applications where a triangular vacuum head is needed for debris removal and center opening against the cartridge being removed before installation Use Darlly 50221 FC 3091 C 5621 PTL25 Filter Cartridge when replacing a worn or dirty cartridge in a compatible filter housing that matches the listed Darlly and equivalent part numbers