Which equation correctly defines pump discharge pressure (PDP)?

• A. PDP = Nozzle Pressure + Total pressure loss
• B. PDP = Nozzle Pressure - Total pressure loss
• C. PDP = Total pressure loss + Friction loss
• D. PDP = Nozzle Pressure + Pressure drop

Answer: (A)

To get the nozzle to the required pressure, you must compensate for what is lost along the hose from pump to nozzle. The nozzle pressure is the pressure you want at the tip, and there are losses everywhere along the path — friction from the hose, fittings, valves, and any elevation changes. To ensure the nozzle sees the intended pressure, you add all those losses to the nozzle pressure. So the pump discharge pressure equals the nozzle pressure plus the total pressure loss. For example, if you need 100 psi at the nozzle and the line losses total 40 psi, the pump discharge pressure should be 140 psi. Subtracting the losses would yield too little pressure at the nozzle, and focusing only on friction loss or using a vague term like "pressure drop" can miss some losses, leading to an incorrect PDP.