Pentair - UltraFlow Plus diffuser O-ring seal - R39006600

Pentair UltraFlow Plus diffuser O-ring seal

This is the genuine Pentair O-ring that seals the diffuser to the pump body on UltraFlow Plus circulation pumps. Listed as item 8 in the official UltraFlow Plus parts diagram, it sits between the diffuser and the pump casing and is essential for maintaining internal hydraulic pressure.

What this O-ring does in the UltraFlow Plus

The diffuser O-ring creates an airtight, watertight seal at the interface between the diffuser and the pump volute. Without an intact seal here, the pump loses prime, develops air ingestion, and fails to deliver rated flow. Replacing this O-ring restores full hydraulic efficiency and stops the internal bypass that causes cavitation noise.

Which UltraFlow Plus models it fits

R39006600 is confirmed to fit the full UltraFlow Plus range across all power variants: models P-UFL-071, P-UFL-073, P-UFL-101, P-UFL-103, P-UFL-151, P-UFL-153, P-UFL-201, P-UFL-203, P-UFL-301, and P-UFL-303. It is also compatible with the Pentair IntelliFlo UltraFlow VSD and the Sta-Rite Ultra-Glas S5P3R pump. Always cross-reference your pump’s model label before ordering.

Signs it needs replacing

A flattened, cracked, or chemically degraded diffuser O-ring typically shows up as a loss of prime that recurs after manual repriming, persistent low-flow alarms on variable-speed controllers, or a faint hissing from inside the pump body at speed. If you disassemble the diffuser and find the O-ring has taken a permanent set — no longer circular in cross-section — replace it before reassembling.

How to install it

Isolate and de-energise the pump, then release system pressure before opening the pump body. Remove the diffuser screws, lift the diffuser clear, and roll out the old O-ring. Clean the groove of any residue, seat the new O-ring dry to check fit, then apply a thin film of silicone-based pool lubricant before final seating. Ensure the O-ring lies flat in its groove with no twist before refitting the diffuser — a pinched O-ring will leak immediately on restart.