Pentair - UltraFlow Plus prefilter hydraulic connection gasket - R39501200

Pentair UltraFlow Plus prefilter hydraulic connection gasket

This is the OEM flat gasket that seals the joint between the prefilter pot and the pump volute on the Pentair UltraFlow Plus. It sits at the hydraulic interface where water passes from the prefilter housing into the pump body, and a failed seal at this point causes air ingestion, loss of prime, and visible weeping around the pot-to-volute joint.

What this gasket does in the UltraFlow Plus

The gasket creates a watertight barrier at the hydraulic connection between the prefilter basket housing and the volute. Without a sound seal here, the pump draws air instead of water, prime is lost repeatedly, and flow rate drops. Because the prefilter housing on the UltraFlow Plus requires weekly inspection and cleaning, this gasket endures frequent removal and reseating cycles — exactly the conditions that accelerate compression set and cracking.

Which UltraFlow Plus models it fits

This gasket is confirmed for the Pentair UltraFlow Plus pump family across single-phase and three-phase variants. Verify your pump’s model reference against the part number R39501200 before ordering if you are working on an older UltraFlow (non-Plus) unit, as housing geometries differ between generations.

Signs it needs replacing

Look for a persistent water weep or mineral staining around the prefilter pot joint — this is the first visible sign. If the pump loses prime shortly after start-up despite a full basket and no blockage in the suction line, suspect this gasket before condemning the shaft seal or impeller. A gasket that has gone hard, brittle, or shows surface cracking will not re-compress correctly no matter how firmly you lock the Cam & Ramp lid.

How to install it

Isolate the pump from supply, vent pressure via the drain plugs, and remove the prefilter lid. Lift out the basket and pull the old gasket from its seat in the pot-to-volute groove — no adhesive is needed or recommended. Seat the new gasket flat into the channel, refit the basket, and lock the Cam & Ramp lid to its stop. Restart the pump and confirm the joint is dry under pressure before returning the system to service. No tools beyond a flathead screwdriver for the drain plugs are required.

Why genuine Pentair matters

The OEM gasket is sized to the exact groove depth and width of the UltraFlow Plus housing. Undersized aftermarket substitutes sit proud of the groove and fail to compress uniformly when the lid locks, leaving a partial air path that no amount of retightening will cure. Specify R39501200 to guarantee the correct cross-section and durometer for this application.