Description
The 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.
IMPORTANT: LUBRICATION REQUIRED SOLD SEPARATELY
Always lubricate this O-ring with a silicone-based lubricant before installation. We carry the Pentair R172351 Lifeguard Silicone Lubricant the OEM-matched product for Pentair equipment.
This 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.
Specifications
| Pentair Part Number | WC9-3 |
| Part Type | O-Ring |
| Color | Black |
| Quantity Included | Each |
| Also Known As / Legacy Brand | Pentair (formerly Sta-Rite) |
Fits Into
| Brand | Equipment Line | Model / Part Number | Notes |
| Pentair (formerly Sta-Rite) | Posi-Flo II Cartridge Filter | PTM50, PTM70, PTM100 | |
| Pentair (formerly Sta-Rite) | Posi-Flo II Cartridge Filter | PTM135 Series | Verify fitment before ordering |
| Pentair (formerly Sta-Rite) | Pool and Spa Filter Separation Tank | Verify fitment before ordering |
Compatibility 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.
Poolaroo Pro Tip
Before 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 Pentair R172351 Lifeguard Silicone Lubricant before seating the O-ring. Do not use petroleum-based lubricants; they will degrade the O-ring material and shorten its service life.
