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What equation does HAMMER use to compute the Darcy-Weisbach friction factor (f) for a pipe with zero initial flow and the Darcy Weisbach friction method (or when the initial flow below the "Flow Tolerance" calculation option).
It uses the Von Karman equation, based on the Roughness height and diameter:DW f = (1.0 / (2.0 * Log10(Diameter / roughness height) + 1.14)^2
Unexpected results seen in pipes with zero initial flow