Pentair - UltraFlow Plus diffuser 0.55–1.10 kW - R39005500

Pentair UltraFlow Plus diffuser 0.55–1.10 kW

This is the genuine OEM diffuser (part R39005500) for Pentair UltraFlow and UltraFlow Plus pool pumps rated between 0.55 kW and 1.10 kW (0.75 HP to 1.5 HP). Positioned between the impeller and the pump body, the diffuser converts the rotational velocity of the impeller into usable pressure, directing water efficiently towards the pump outlet. Without a serviceable diffuser, the pump loses hydraulic efficiency and flow rate drops noticeably.

What this diffuser does in the UltraFlow Plus

The diffuser sits directly behind the impeller inside the pump’s wet end. As the impeller spins, it accelerates water outward; the diffuser’s shaped channels decelerate that flow and convert kinetic energy into pressure head. A cracked, warped, or eroded diffuser breaks this energy transfer — output pressure falls, priming becomes sluggish, and the motor runs harder than it should. Replacing it restores the pump to its rated hydraulic curve.

Which UltraFlow Plus models it fits

R39005500 is the correct diffuser for UltraFlow Plus 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 — covering the 0.55 kW to 1.10 kW power band. It does not fit the 1.50 kW or 2.20 kW variants; those use part R39015500. Cross-check your pump’s model plate before ordering.

Signs it needs replacing

A failing diffuser typically presents as reduced flow at the return jets despite a clean basket and filter, difficulty priming — especially after a shutdown — or audible cavitation noise from the pump wet end. Visible cracks, chips around the diffuser vanes, or heat distortion are immediate grounds for replacement. Left unaddressed, a damaged diffuser accelerates wear on the impeller and mechanical seal.

How to install it

Isolate and drain the pump, then remove the stainless-steel band clamp to separate the power end from the wet end. Unscrew the impeller lock screw (R39009900), lift out the impeller, and the diffuser lifts straight out of its recess. Fit the new diffuser, ensuring the locating tab seats correctly, then reassemble in reverse order. The full procedure takes around 20 minutes with basic hand tools and does not require specialist equipment.