What is the net pump discharge pressure (NPDP) when pumping at 170 psi with 50 psi incoming from a hydrant?

Answer: B — 120 psi

To determine the net pump discharge pressure (NPDP), you subtract the incoming pressure, often referred to as the intake pressure or static pressure, from the discharge pressure of the pump. In this scenario, the pump is discharging water at a pressure of 170 psi, and the incoming pressure from the hydrant is 50 psi. The calculation for NPDP is straightforward: NPDP = Pump Discharge Pressure - Incoming Pressure Using the numbers provided: NPDP = 170 psi - 50 psi NPDP = 120 psi Thus, with the calculated NPDP being 120 psi, this answer reflects the actual pressure available for fighting fires or supplying water after accounting for the incoming pressure from the hydrant. Understanding how to calculate NPDP accurately is crucial for drivers/operators to assess the effective pressure their pump can deliver for firefighting operations.