At the same GPM, which statement about nozzle pressures is true?

At the same GPM, which statement about nozzle pressures is true?

• A. Fog nozzles require the same nozzle pressure as smooth bore.
• B. Smooth bore nozzles use higher nozzle pressure than fog nozzles.
• C. Nozzle pressure depends on nozzle type but not on GPM.
• D. Fog nozzles typically operate at higher nozzle pressures than smooth bore nozzles for the same flow.

Answer: (D)

At a given flow rate, the pressure at the nozzle depends on how the nozzle produces the spray. Fog nozzles atomize water into a fine mist by forcing it through restrictive passages and shear processes, which adds resistance and requires more energy. Smooth-bore nozzles deliver water as a relatively coherent jet with fewer internal losses, so the same volume can exit at a lower pressure. Therefore, for the same GPM, fog nozzles operate at higher nozzle pressures than smooth-bore nozzles.

At a given flow rate, the pressure at the nozzle depends on how the nozzle produces the spray. Fog nozzles atomize water into a fine mist by forcing it through restrictive passages and shear processes, which adds resistance and requires more energy. Smooth-bore nozzles deliver water as a relatively coherent jet with fewer internal losses, so the same volume can exit at a lower pressure. Therefore, for the same GPM, fog nozzles operate at higher nozzle pressures than smooth-bore nozzles.