Using the subtract 10 method, what is the calculated pump discharge pressure for 300 ft of 2.5 inch hose with a nozzle pressure of 50 psi?

• A. 145 psi
• B. 74 psi
• C. 50 psi
• D. 80 psi

Answer: (D)

Friction losses in the hose add to the pressure you need at the pump to deliver the required nozzle pressure. The subtract 10 method uses a rough rate of 10 psi per 100 feet of 2.5 inch hose. For 300 feet, that’s 3 × 10 = 30 psi of friction loss. Add that to the nozzle pressure of 50 psi: 50 + 30 = 80 psi. So the pump discharge pressure is 80 psi. This is a quick rule-of-thumb calculation; actual friction depends on flow and hose conditions, but this aligns with the given method.