If residual drops 11%-15%, what multiplier applies to main flow?

• A. 3X more
• B. 2X more
• C. 1X more
• D. 0

Answer: (B)

When you’re setting pump discharge, residual pressure readings show how much pressure is left after water is moving through the hose line. A residual in the 11–15% range means there’s a notable loss of pressure due to friction and elevation along the line. To compensate and still deliver sufficient nozzle pressure and flow, the practical rule of thumb is to apply a twofold multiplier to the main flow. In other words, you estimate that the main flow needs to be about twice the flow you’d infer from a higher-residual scenario to overcome those line losses and reach the target nozzle performance. Using a larger multiplier would overestimate the needed flow for this residual range, while a smaller (or zero) multiplier wouldn’t overcome the friction losses. So, twofold is the appropriate multiplier for residuals in this 11–15% range.