If you are supplying Reserve Truck 14 through 100' of 5" hose with a hydrant pressure of 75 psi, how do you calculate friction loss if the GPM is unknown?

The correct approach to calculate friction loss in this scenario involves understanding that friction loss is influenced by several factors, including the flow rate (GPM) of water passing through the hose, the length of the hose, and the diameter of the hose. Even without a specific GPM value, one can still make certain assumptions and perform calculations based on the available pressure.

When calculating friction loss, using the available pressure allows you to assess how much pressure is lost due to friction as the water moves through the hose. Depending on the type of hose and its diameter, there are standard formulas and charts available that correlate typical flow rates with friction loss over certain distances and sizes of hoses. By using the given hydrant pressure and assuming reasonable flow rates typically associated with a 5" hose, you can estimate the friction loss.

This method enables you to maintain a safe and effective operation when supplying water, ensuring that the pressure at the end of your hose is adequate for firefighting or other needs. Therefore, calculating based on available pressure is a practical and effective means of determining friction loss when the specific GPM is not known.