NFPA 1002 Pump Operations Practice Test

How does hose diameter affect friction loss and discharge pressure for a given nozzle flow?

A larger diameter increases friction loss and requires higher discharge pressure. A larger diameter has no effect on friction loss or discharge pressure. A larger diameter reduces friction loss and lowers the discharge pressure needed to achieve the same nozzle pressure. A larger diameter increases nozzle pressure requirements for the same flow.

Correct Answer:

A larger diameter reduces friction loss and lowers the discharge pressure needed to achieve the same nozzle pressure.

Explanation:

When you push the same amount of water through a hose, the friction the water experiences along the hose depends on how fast it’s moving inside that hose. A larger diameter means the water velocity for the same flow is lower, which reduces the friction interaction with the hose walls. With less friction loss, the pump doesn’t have to work as hard to push the water to the nozzle. So, for a fixed nozzle flow, a larger hose diameter lowers the SAMPLEfriction loss and, consequently, lowers the discharge pressure the pump must supply to maintain the same nozzle pressure. The idea that larger diameter would increase friction loss or do nothing to friction loss isn’t supported by how flow and wall friction relate to diameter.

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