Pump Discharge Pressure

PDP is the number the operator is really chasing at the panel. Start from the pressure the nozzle is built around, then add back everything the water gives up on the way there: friction loss in the hose, any appliance in the lay, and the pressure gained or lost from elevation. Set the throttle so the discharge gauge reads that total and the tip ends up where it should be.

Because friction loss grows with the square of the flow, PDP is not a single fixed number for a given line — it climbs steeply as you move more water. That is why a longer stretch or a bigger nozzle can demand a much higher pump pressure even though the tip pressure target never changed.