Blank pressure is defined as the difference between the pump discharge pressure and the incoming pressure from the hydrant. What is this pressure commonly called?

• A. Net pump discharge
• B. Net hydrant pressure
• C. Static pressure
• D. Residual pressure

Answer: (A)

The main idea is to understand what the pump is actually contributing to the water pressure. The difference between what the pump is discharging and what the hydrant is delivering as it enters the pump is called the net pump discharge pressure. This value shows the effective pressure the pump adds to push water through the hose to the nozzle, accounting for the hydrant supply.

For example, if the pump discharge gauge reads 140 psi and the hydrant supply brings in 60 psi, the net pump discharge pressure is 80 psi. This net pressure is what you rely on to overcome friction losses in the hose and to achieve the required nozzle pressure.

The other terms don’t fit because static pressure describes pressure without flow, residual pressure refers to the pressure remaining in the system at a point while water is flowing (not the pump’s added pressure), and net hydrant pressure would refer to the hydrant’s supply alone without considering the pump’s contribution.