ONE FORMULA, ONE ANSWER
Joukowsky Water Hammer Pressure Change Calculator
Estimate the initial pressure wave generated at a downstream disturbance and travelling upstream after a rapid change in liquid speed. Choose input units and calculate one value within the stated conditions.
Inputs
Calculations run in this browser. Scientific notation such as 1.2e-3 is supported. Do not group thousands.
Result
Initial pressure change Δp
Enter values and select Calculate.
Δp = ρa(Vinitial − Vfinal)
Assumptions
Required: an initially liquid-filled uniform elastic pipe and a one-dimensional initial wave, with velocity-change duration no greater than round-trip time 2L/a. A positive initial-minus-final speed reduction gives a pressure rise. Excluded: reflections, branches, friction recovery, gas and vapor collapse. This result is not a guaranteed system-wide maximum pressure.
Displayed values are floating-point approximations. Design safety factors and unprovided error contributions are not calculated.
Formula references and credits
NaNa Lab created the code, descriptions, icons and preview images. Text, figures and code from the linked references have not been reproduced.
Physical constants: NIST / CODATA 2022. The values of μ₀ and ε₀ are measured recommendations, not exact defining constants. Values and precision notes are in the source record.
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