In the Road Acceptance Test braking calculation, PDP equals NP plus which term?

• A. Total Pressure Loss
• B. Hydraulic Pressure Lapse
• C. Pressure Drop
• D. Friction Loss

Answer: (A)

In this braking calculation, you must cover the pressure needed at the nozzle plus all the losses the water encounters on the way from the pump to the nozzle. The pump discharge pressure (PDP) is what the pump must produce to overcome those drops, so it equals the nozzle pressure (the pressure you want at the nozzle) plus the total pressure losses along the line.

Total Pressure Loss represents every drop in pressure from pump discharge to nozzle: friction losses in hoses, losses through fittings, valves, adapters, and any elevation changes. It’s the complete sum of resistance the fluid faces as it travels through the system.

If the nozzle pressure you need is, say, 100 psi and the total pressure loss is 25 psi, then the pump discharge pressure must be 125 psi to deliver the desired nozzle pressure.

Other terms don’t capture the full picture: friction loss is only one part of the losses, while the calculation here uses the total of all losses, which is why the correct term is Total Pressure Loss.