Work out water hammer pressure instantly with clear inputs, formula shown and shareable results.
The Joukowsky equation gives the maximum surge for instantaneous closure as rho x wave speed x velocity change. Closure counts as rapid if it happens within the critical time 2L/a, the time for the pressure wave to travel to the reservoir and back. Slower closure reduces the surge roughly in proportion.
Joukowsky surge
Δp = rho x a x Δv
Critical time
Tc = 2L / a; slow closure surge = full surge x Tc / closure time
Preliminary estimate only. Surge analysis for pumping mains and long pipelines should be carried out with transient modelling by a qualified engineer.
Δp = rho x a x Δv. The Joukowsky equation gives the maximum surge for instantaneous closure as rho x wave speed x velocity change.
Slow the valve closure beyond the critical time, lower the operating velocity, shorten the pipe run, or install a surge vessel or air chamber to absorb the wave.
This calculator takes 4 inputs: Initial flow velocity, Pressure wave speed, Pipe length to the reservoir, Valve closure time. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.