_____ is the pressure remaining at the source while water is flowing.

• A. Residual Pressure
• B. Dynamic Pressure
• C. Atmospheric Pressure
• D. Flow Pressure

Answer: (A)

Residual pressure is the pressure that remains at the pump/source once water has started flowing. When water moves through hoses and fittings, friction and other losses reduce the pressure from the static value. The pressure you still have at the source while the flow is ongoing is the residual pressure. This concept helps firefighters gauge how much pressure is being lost in the line and ensures there’s enough pressure at the nozzle to reach the target.

Atmospheric pressure is simply the surrounding air pressure and isn’t about the hydraulic pressure in the system. Dynamic pressure is related to the water’s velocity rather than the pressure remaining at the source during flow. Flow pressure is a term some use for pressure during flow at the discharge or nozzle, but the specific notion described here is the remaining source pressure—residual pressure.