Pentair WhisperFlo® 075254 Power End Sub Assembly for WF-6, WF-28 1 HP Full Rated 1-1 per 5 HP Up Rated High Performance Pump - The Pentair Energy Efficient Power End Sub Assembly works with the first and only single-speed pump models to use NEMA Premium® Efficient motors for pool applications. Meaning you get balanced flow and greater efficiency in your single-speed, single-phase, Permanent Split Capacitor motor, greatly reducing operating costs.