When flow is suddenly stopped, flow inertia causes a pressure surge at the valve, with a shockwave propagating through the pipeline. This is also known as Water Hammer and can cause considerable damage. Engineers need to know the maximum pressure surge to correctly design the pipe, valve andother fittings.

Water hammer is a common phenomenon. For example, the audible creaking when taps are shut off in kitchens or bathrooms results from the Water Hammer effect

These are the equations implemented in the spreadsheet.

where

- K is the bulk modulus of the liquid (Pa)
- ρ is the liquid density (kg m
^{-3}) - D is the pipe diameter (m)
- t is the pipe wall thickness (m)
- E is the Young's Modulus of the pipe (Pa)
- c is the speed of sound in the pipe (m s
^{-1}) - Δv is the velocity of the liquid before the valve is shut (m s
^{-1}) - ΔP is the maximum pressure (at the valve) generated by the valve closure(Pa)

Δv can be easily calculated by the Darcy-Weisbach equation. ΔP is also known as the Joukowsky Pressure.

These equations do not predict the pressure surge arising from column separation (which may be higher than the Joukowsky Pressure). Column separation references the breaking of liquid columns in filled pipes.

Download Excel Spreadsheet for Water Hammer