JIBC Exterior Practice Exam

The main idea is that friction loss in a hose depends on how fast the water has to move through the hose, which is set by the hose’s diameter for a given flow. A larger diameter hose lets water flow more slowly for the same discharge, so the friction loss per length is reduced. With less friction loss, the pump doesn’t have to work as hard to push water to the nozzle, so you can either maintain the same nozzle pressure with less pump pressure or achieve higher flow while keeping the nozzle pressure lower.

Conversely, a smaller diameter hose forces water to move faster for the same flow, which increases friction losses along the hose. That means more pump pressure is needed to keep the nozzle at the desired pressure, or the available flow is reduced if pump pressure is fixed.

So, larger diameter hoses reduce friction loss and allow higher flows with lower nozzle pressures; smaller hoses have higher friction loss and require more pressure to maintain nozzle pressure.