Pentair 8 1/2" Quad Closure Top O-Ring

The Pentair 8-1/2" Quad Closure Top O-Ring (part number 178543Z) is a precision-molded sealing gasket engineered specifically for heavy-duty Pentair filtration systems, including Quad D.E. (diatomaceous earth) and Clean & Clear Plus cartridge filters. Fabricated from a robust, chemical-resistant synthetic rubber (EPDM) compound, this large circular gasket sits directly in the sealing channel where the upper filter lid meets the lower tank body. Its primary functional role is to provide a comprehensive airtight and watertight seal when the metal tension clamp is torqued down, allowing the system to safely handle intense internal hydraulic pressures without leaking. Designed to maintain its structural elasticity despite prolonged contact with chlorine, acid, and fluctuating water temperatures, this specialized O-ring ensures consistent sealing integrity across seasons. Due to its large 8.5-inch nominal diameter and thick cross-sectional profile, this durable rubber component has a product and shipping weight of approximately 0.25 pounds (about 4 ounces), offering a substantial yet easily manageable replacement piece for routine filter maintenance.