Sta-Rite Diffuser O-Ring for PLBC Booster Pump, U9-199

The Sta-Rite U9-199 is the diffuser o-ring for the PLBC booster pump, model PLBC-178L. It is the genuine Sta-Rite replacement for that position.

What it seals

A booster pump exists to give a pressure side cleaner more head than the filter pump can supply. The impeller does that work, and the diffuser directs the flow it produces. The o-ring between the diffuser and the housing is what stops pressurized water from circling back inside the pump. When it hardens or takes a set, the pump still runs and still sounds normal, but the cleaner gets less pressure than it should and starts to crawl.

Fitting

The diffuser is exposed as soon as the pump is opened, so this o-ring is worth changing during any PLBC service, particularly a shaft seal replacement. Seat it clean and dry into its groove and check the diffuser for cracks before you put the pump back together.