Which statement correctly describes how nozzle pressure and friction loss relate to pump discharge pressure?

• A. PDP equals NP minus FL
• B. PDP equals NP
• C. PDP equals FL
• D. PDP equals NP plus FL

Answer: (D)

In hose line hydraulics, the pump discharge pressure is the total pressure the pump must produce to push water from the pump all the way to the nozzle while maintaining the required spray. The nozzle pressure is the pressure you need at the nozzle to achieve the desired flow and pattern, and friction loss is the pressure drop that occurs as water travels through the hose, fittings, and any appliances. To deliver the right pressure at the nozzle, you must overcome those losses and still provide the nozzle pressure, so you add them together. That makes the pump discharge pressure equal to nozzle pressure plus friction loss. For example, if you need 60 psi at the nozzle and the hose losses 40 psi along the way, the pump discharge pressure should be 100 psi. Subtracting friction would under-pressurize at the nozzle, and considering only friction would ignore the required nozzle pressure. In more complex setups you’d also account for elevation or appliance losses, but the core relationship remains PDP = NP + FL.