Firefighter Practice Exam

Which calculation can be used to determine the amount of pressure loss due to hose length, when friction is constant?

1. Direct addition of psi values

2. Proportionate scaling of lengths

3. Multiplication of pressure values

4. Thermal conversion

The correct answer is: Proportionate scaling of lengths

To determine the amount of pressure loss due to hose length while keeping friction constant, the most appropriate method involves proportionate scaling of lengths. This approach takes into account that pressure loss in a hose is influenced by both the length of the hose and the flow characteristics through it. When hose length increases, the frictional loss also increases, leading to a reduction in pressure at the end of the hose. By understanding the relationship between the length of the hose and the accompanying pressure loss, firefighters can estimate how much pressure will be lost over a given length. This method utilizes a ratio to determine the pressure loss based on the length of hose in comparison to a known or baseline measurement, thus allowing for accurate pressure calculations while ensuring that other variables, like friction, are maintained constant. Other methods mentioned do not effectively isolate the variables affecting pressure loss in a hose. For instance, direct addition of psi values does not account for the complexities of flow and length. Multiplication of pressure values lacks a context of how hose characteristics interact with the length, and thermal conversion is unrelated to pressure loss in hose lines. Therefore, proportionate scaling provides the necessary framework to accurately determine pressure loss due to hose length under constant friction conditions.