What term describes the pressure difference between the pump discharge pressure and hydrant pressure?

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

Answer: (A)

The main idea here is the pressure a pump must add beyond what the hydrant already provides. Net pump discharge pressure is the difference between the pump’s discharge pressure and the hydrant pressure. It represents the actual pressure available to push water through hoses to the nozzle after accounting for the hydrant’s supply pressure.

For example, if the pump is delivering 150 psi at the discharge and the hydrant pressure is 70 psi, the net pump discharge pressure is 80 psi. This is the pressure that will drive the water through the hose and into the nozzle, overcoming friction losses and elevation where applicable.

Static pressure is the pressure present with no flow, which isn’t a difference between two pressures. Atmospheric pressure isn’t what’s being referenced in this context, and residual pressure refers to the pressure remaining in the system while water is flowing, not the difference between pump discharge and hydrant pressure.