Which statement best describes the effect of nozzle design on pressure for a given flow?

• A. Nozzle design determines the precise pressure required to deliver a given flow.
• B. Nozzle design has no impact on required pressure.
• C. Nozzle pressure is always the same regardless of design.
• D. Nozzle pressure cannot be predicted.

Answer: (A)

The main idea is that nozzle characteristics set the pressure needed to push a given amount of water through the nozzle. The nozzle acts as a restriction in the flow path, and how easily water can pass through it depends on its size and shape (the exit area and how the flow coefficient behaves). For a fixed flow rate, a smaller or more restrictive nozzle requires a larger pressure difference to overcome the resistance and drive the water through; a larger or less restrictive nozzle needs less pressure. In firefighting terms, the pump discharge pressure must supply the nozzle pressure plus any losses in the hose and fittings, so changing the nozzle design changes the pressure you need to achieve the same flow. Since nozzle design directly governs this relationship, it determines the pressure required for a given flow.