Which of the following primarily affects the capacity of a fire pump?

The capacity of a fire pump is fundamentally determined by its design and specifications, which are outlined by the manufacturer's ratings for flow rate (gallons per minute or GPM) and pressure (pounds per square inch or PSI). When considering pump capacity, it’s important to realize that this value indicates the maximum amount of water the pump can deliver under optimal conditions.

Factors like hose length, water temperature, and pump drive type can influence overall performance and efficiency, but they do not change the inherent capacity of the pump itself as defined by its mechanical capabilities. For instance, while longer hoses may create friction loss that can affect the effective flow at the end of the hose, the pump's rated capacity remains the same. Similarly, water temperature can affect viscosity, but it does not alter the design or maximum output of the pump. The type of drive mechanism—whether it's direct drive or gear-driven—may influence operational efficiency, but does not change the designated capacity.

Thus, the primary factor that dictates the capability of a fire pump remains its pumping capacity, making that choice the most accurate in addressing the original question regarding what primarily influences a fire pump's capacity.