The Pentair Diffuser Seal (355331Z) is the OEM replacement sealing O-ring for the diffuser assembly on the Pentair Challenger, SuperFlo VS/VST, and SuperMax VS pump lines. IMPORTANT: LUBRICATION REQUIRED — SOLD SEPARATELYAlways 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. IMPORTANT: MANUFACTURE DATE APPLIES TO SOME MODELSFor SuperFlo VS/VST and SuperMax VS pumps, this seal applies to units manufactured after 06/17/19. Verify your pump's manufacture date on the motor nameplate before ordering. This seal maintains the pressure differential across the diffuser within the pump wet end, keeping water directed efficiently through the impeller. A worn or damaged diffuser seal allows internal recirculation, which reduces flow rate and pump efficiency. Replacing this seal at the first sign of performance loss restores the pump's designed hydraulic output. Specifications Pentair Part Number 355331Z Part Type Diffuser Seal (O-Ring) Quantity Included Each (1) Fits Into Brand Equipment Line Model / Part Number Notes Pentair SuperFlo VS Variable Speed Pump — SuperFlo VS/VST Series SUPERFLO VS — Pentair SuperFlo VST Variable Speed Pump — SuperFlo VS/VST Series SUPERFLO VST — Pentair SuperFlo VS/VST Variable Speed Pump — SuperFlo Series SUPERFLO VS/VST Mfg. After 06/17/19 Pentair SuperFlo VS/VST Variable Speed Pump — SuperFlo Series SUPERFLO-VS-VST Mfg. After 06/17/19 Pentair SuperMax VS Variable Speed Pump — SuperMax Series SUPERMAX VS Mfg. After 06/17/19 Pentair SuperMax VS Variable Speed Pump — SuperMax Series SUPERMAX-VS Mfg. After 06/17/19 Pentair Challenger High Pressure Pump — Challenger Series CHALLENGER Diffuser O-ring Pentair Challenger High Pressure Pump — Challenger Series CHALLENGER HIGH PRESSURE PUMP Diffuser O-ring Pentair Challenger High Flow Pump — Challenger High Flow Series CFII-N1-5FE 5 HP only 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. Pro Tip Before seating this seal, clean the diffuser O-ring groove completely — any residue from the old seal will prevent a proper seating and cause the new seal to leak under pressure. Apply a thin, even coat of silicone-based lubricant — Pentair R172351 Lifeguard Silicone Lubricant is the OEM-matched option — before installation. Never use petroleum-based lubricants; they degrade elastomer O-rings and will cause premature seal failure.
