What does the "P" mean on the 230 Micro Pump adjustment knob?

The “P” indicates the preferred priming position. All 230 Micro Pumps are self-priming and capable of drawing a vacuum, but the adjustment knob must be turned with the “P” aligned to the mark on the pump body to confirm it is set to the priming position.

For normal operation, it is recommended to keep the pump in the priming position unless the required output cannot be reached by lowering the cycle rate. Keeping the pump in this position helps ensure that any air bubbles are pushed through the system if the reservoir runs out of fluid.