Which factor most directly affects the discharge pressure when the engine speed is constant?

Which factor most directly affects the discharge pressure when the engine speed is constant?

• A. Water temperature in the line.
• B. Ambient weather conditions.
• C. Length of the hose from pump to nozzle.
• D. Friction losses along the lines.

Answer: (D)

Discharge pressure is driven by the resistance the water meets as it travels from pump to nozzle. When the engine speed is held constant, the pump tends to push a steady flow, so the pressure it must generate mainly balances the friction losses along the lines. These losses increase with hose length (and with the amount of flow through the line and the number of fittings), so a longer hose means greater friction losses and thus higher discharge pressure to maintain the same flow. Water temperature and ambient weather have only small, indirect effects—mostly minor changes in water viscosity or slight environmental influences—so they don’t directly dictate discharge pressure the way friction losses along the lines do.

Discharge pressure is driven by the resistance the water meets as it travels from pump to nozzle. When the engine speed is held constant, the pump tends to push a steady flow, so the pressure it must generate mainly balances the friction losses along the lines. These losses increase with hose length (and with the amount of flow through the line and the number of fittings), so a longer hose means greater friction losses and thus higher discharge pressure to maintain the same flow. Water temperature and ambient weather have only small, indirect effects—mostly minor changes in water viscosity or slight environmental influences—so they don’t directly dictate discharge pressure the way friction losses along the lines do.