{"product_id":"pentair-black-o-ring-select-sta-rite-pool-spa-cartridge-filters-wc9-3","title":"Pentair Black O-Ring | Sta-Rite Posi-Flo II Cartridge Filters | WC9-3","description":"\u003cp\u003eThe Pentair WC9-3 is the OEM replacement black O-ring for Sta-Rite Posi-Flo II pool and spa cartridge filters, keeping the filter housing sealed and operating at full efficiency.\u003c\/p\u003e\n\n\u003cp style=\"background-color: #fff3cd; border: 2px solid #FFEAA7; padding: 15px; border-radius: 5px; margin: 15px 0; color: #856404;\"\u003e\u003cstrong\u003eIMPORTANT: LUBRICATION REQUIRED — SOLD SEPARATELY\u003c\/strong\u003e\u003cbr\u003eAlways lubricate this O-ring with a silicone-based lubricant before installation. We carry the \u003ca href=\"https:\/\/poolaroo.com\/products\/pentairwaterpoolandspainc_r172351\" alt=\"Pentair R172351 Lifeguard Silicone Lubricant\"\u003ePentair R172351 Lifeguard Silicone Lubricant\u003c\/a\u003e — the OEM-matched product for Pentair equipment.\u003c\/p\u003e\n\n\u003cp\u003eThis O-ring maintains the pressure seal on Sta-Rite Posi-Flo II cartridge filter housings. A worn or cracked O-ring allows air into the system and water to bypass the filter element, resulting in pressure loss and reduced filtration performance. Replacing this O-ring restores a proper housing seal.\u003c\/p\u003e\n\n\u003ch3\u003eSpecifications\u003c\/h3\u003e\n\u003ctable style=\"width: 100%; border-collapse: collapse; margin: 20px 0; border: 1px solid #ccc;\"\u003e\n\u003ctr style=\"background-color: #f8f9fa;\"\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e\u003cstrong\u003ePentair Part Number\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003eWC9-3\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #ffffff;\"\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e\u003cstrong\u003ePart Type\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003eO-Ring\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #f8f9fa;\"\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e\u003cstrong\u003eColor\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003eBlack\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #ffffff;\"\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e\u003cstrong\u003eQuantity Included\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003eEach\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #f8f9fa;\"\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e\u003cstrong\u003eAlso Known As \/ Legacy Brand\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003ePentair (formerly Sta-Rite)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/table\u003e\n\n\u003ch3\u003eFits Into\u003c\/h3\u003e\n\u003ctable style=\"width: 100%; border-collapse: collapse; margin: 20px 0; border: 1px solid #ccc;\"\u003e\n\u003ctr style=\"background-color: #f8f9fa;\"\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e\u003cstrong\u003eBrand\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e\u003cstrong\u003eEquipment Line\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e\u003cstrong\u003eModel \/ Part Number\u003c\/strong\u003e\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e\u003cstrong\u003eNotes\u003c\/strong\u003e\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #ffffff;\"\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003ePentair (formerly Sta-Rite)\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003ePosi-Flo II Cartridge Filter\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003ePTM50, PTM70, PTM100\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e—\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #f8f9fa;\"\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003ePentair (formerly Sta-Rite)\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003ePosi-Flo II Cartridge Filter\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003ePTM135 Series\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003eVerify fitment before ordering\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr style=\"background-color: #ffffff;\"\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003ePentair (formerly Sta-Rite)\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003ePool and Spa Filter Separation Tank\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003e—\u003c\/td\u003e\n\u003ctd style=\"border: 1px solid #ccc; padding: 10px;\"\u003eVerify fitment before ordering\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/table\u003e\n\u003cp\u003e\u003cem\u003eCompatibility is based on Pentair parts documentation and available OEM records. This is not an exhaustive list. For certainty, verify the part number in your equipment's manual or on the original part itself before ordering.\u003c\/em\u003e\u003c\/p\u003e\n\n\u003ch3\u003ePoolaroo Pro Tip\u003c\/h3\u003e\n\u003cp\u003eBefore installing this O-ring, clean the groove in the filter housing to remove any debris or residue from the old O-ring. Apply a thin, even coat of silicone-based lubricant — we recommend the \u003ca href=\"https:\/\/poolaroo.com\/products\/pentairwaterpoolandspainc_r172351\" alt=\"Pentair R172351 Lifeguard Silicone Lubricant\"\u003ePentair R172351 Lifeguard Silicone Lubricant\u003c\/a\u003e — before seating the O-ring. Do not use petroleum-based lubricants; they will degrade the O-ring material and shorten its service life.\u003c\/p\u003e\n\n\u003c!-- wft:processed:manual:2026-05-01 --\u003e","brand":"Pentair","offers":[{"title":"Default Title","offer_id":52772586291475,"sku":"WC9-3","price":39.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0920\/0687\/5411\/files\/pentair-black-o-ring-sta-rite-cartridge-filter-wc9-3.webp?v=1766190462","url":"https:\/\/poolaroo.com\/products\/pentair-black-o-ring-select-sta-rite-pool-spa-cartridge-filters-wc9-3","provider":"Poolaroo","version":"1.0","type":"link"}