If nozzle pressure is 60 psi and there is a friction loss of 20 psi along the attack line plus an elevation head of 10 psi, what discharge pressure should the pump be set to?

• A. 60 psi only.
• B. 60 + 20 + 10 = 90 psi.
• C. 60 + 20 = 80 psi.
• D. 60 + 10 = 70 psi.

Answer: (B)

To deliver the required depth at the nozzle, you must overcome all system losses and still maintain the nozzle pressure. The nozzle needs 60 psi, and there are two additional losses to overcome along the attack line: friction loss of 20 psi and an elevation head of 10 psi. The pump discharge pressure must equal the sum of the nozzle pressure and these losses: 60 + 20 + 10 = 90 psi. So, set the pump discharge to 90 psi to ensure the nozzle ends up at 60 psi.