In calculating pump discharge pressure, friction loss is added to which value?

• A. Nozzle pressure
• B. Friction loss
• C. Total pump discharge pressure
• D. Atmospheric pressure

Answer: (A)

The main idea is that you must deliver a specific pressure at the nozzle, and friction in the hose reduces the pressure as water moves toward the nozzle. The nozzle pressure is the target pressure at the end of the hose, so to make sure that pressure actually reaches the nozzle, you must compensate for the pressure lost due to friction. That means you add the friction loss to the nozzle pressure to get the pump discharge pressure. For example, if you need 50 psi at the nozzle and the hose causes 20 psi of friction loss, you set the pump discharge pressure to 70 psi. Atmospheric pressure isn’t used in this gauge-based calculation, and the pump discharge pressure is the result, not the value you add friction loss to. The friction loss specifically increases the nozzle pressure to determine the pump discharge pressure.