When using three unequal lengths of hose to supply a monitor, how is gallons per minute (GPM) calculated?

When supplying a monitor with three unequal lengths of hose, calculating the gallons per minute (GPM) effectively requires an understanding of how friction loss affects water flow. The approach of using the higher pressure for friction loss is correct because the friction loss increases with the length and diameter of the hose and is further influenced by the amount of pressure in the system.

In scenarios where you have multiple hoses with varying lengths, the pressure at the end of the longest hose will dictate the flow rate due to the highest friction loss it experiences. By using the higher pressure for friction loss calculations, you ensure that you account for the worst-case scenario in terms of pressure drop, which is crucial for accurately determining GPM. This method provides a conservative estimate that helps guarantee adequate flow to the monitor under all conditions, especially when dealing with uneven hose lengths that may cause variable friction losses.

In contrast, averaging pressures or using the lower pressure without consideration of the actual operating conditions could lead to underestimating the friction loss, which could jeopardize the effectiveness of the water supply to the monitor. The calculation of GPM is not simply a function of total hose length divided by time; it's a more complex interaction of pressures influenced by the specific conditions of your setup.