Which method is commonly used to calculate the flow rate through a nozzle?

The 29.7 formula is commonly used to calculate the flow rate through a nozzle in firefighting applications. This formula is derived from empirical data and provides a straightforward method for estimating the flow in gallons per minute (GPM) based on the diameter of the nozzle and the pressure at which water is being delivered. Specifically, the formula states that the flow rate in GPM can be approximated by multiplying the square root of the nozzle pressure (in pounds per square inch) by 29.7, giving responders a quick and effective way to assess water delivery capabilities when deploying hose lines.

Other methods, while relevant in fluid mechanics, are not specifically tailored for the practical needs of fire operations in the same accessible manner. For example, Bernoulli's theorem relates to the principles of energy conservation in fluid flow but is more suited for theoretical applications. The Venturi effect illustrates how fluid velocity increases as it passes through a constricted section, which is useful in certain contexts but not typically employed for direct flow rate calculations in firefighting. Pascal's principle deals with fluid pressure transmission in confined spaces and does not provide a means to calculate flow rates through nozzles. Thus, the 29.7 formula stands out as the practical choice for driver operators