Water Hammer Calculator

Calculate pressure surge from instantaneous valve closure using the Joukowsky equation.

Pipe Networks · Transient

Fluid Presets

Inputs

Initial flow velocity V (m/s)

Acoustic wavespeed a (m/s)

Fluid density ρ (kg/m³)

Theory

Joukowsky Equation:

ΔP = ρ × a × ΔV

Where:

ρ = fluid density [kg/m³]
a = acoustic (pressure wave) speed in the pipe [m/s]
ΔV = change in flow velocity (= V for full instantaneous closure) [m/s]

Typical wavespeed values (water-filled pipes):

Pipe material	a (m/s)	a (ft/s)
Steel	1000–1400	3280–4590
Cast iron	900–1300	2950–4260
Concrete	1000–1300	3280–4260
PVC	300–500	980–1640
HDPE	200–400	660–1310

Water hammer is a transient pressure surge caused by rapid valve closure. The Joukowsky equation gives the maximum surge for instantaneous closure. Slow closure over more than 2L/a seconds (the pipe period) reduces the surge proportionally.