PipeSageWhen to use this calculator
The Joukowsky equation gives the peak pressure surge from an instantaneous change in flow velocity — a valve slamming shut, a pump tripping offline. Wave speed (a) depends on fluid compressibility and pipe stiffness; roughly 1200–1400 m/s for water in steel pipe, lower in plastic pipe. If actual valve closure time is longer than the critical closure time (2L/a), the surge is reduced below the full Joukowsky value — closing slower than this threshold meaningfully cuts the surge.