Wasser hammer — Druck surge in pipes

Overview

Water hammer (hydraulic shock) is a pressure surge caused by sudden changes in fluid velocity in a pipe system. It occurs when:

• Valves close rapidly
• Pumps start or stop suddenly
• Check valves slam shut

Joukowsky Equation

The maximum pressure rise from instantaneous valve closure:

$\Delta p = \rho \cdot c \cdot \Delta v$

where:

• $\Delta p$ = pressure surge (Pa)
• $\rho$ = fluid density (kg/m³)
• $c$ = speed of sound in the pipe-fluid system (m/s)
• $\Delta v$ = change in velocity (m/s)

The wave speed in an elastic pipe:

$c = \sqrt{\frac{K/\rho}{1 + (K \cdot D)/(E \cdot t)}}$

where $K$ = fluid bulk modulus, $E$ = pipe elastic modulus, $D$ = pipe diameter, $t$ = wall thickness.

Typical Wave Speeds

Prevention Methods