Water Hammer — Joukowsky

The pressure surge on valve closure, the wave speed, and the effect of closing time.

Unit system

Inputs

Pipe sizeSchedulePipe materialFlow velocity

The surge is DIRECTLY proportional to velocity. Halving the velocity halves the hammer.Line length up to the valve

Closing time (s)

The critical time is 2L/a. Closing faster than that gives the FULL surge; slowing it down is the one cheap fix.Water temperature

Line operating pressure (absolute)

Pressure surge

7.776bar a

Peak pressure (line + surge)

12.78bar a

Verdict	The peak is more than twice the operating pressure — check the line and its anchors against this load
Pressure wave speed	1,371 m/s
Critical closing time 2L/a (s)	0.2918
Surge if closed instantly	26.65 bar a
Peak ÷ operating pressure	2.56

The Joukowsky relation is for INSTANT closure and gives the UPPER BOUND. Beyond the critical time the surge is scaled down proportionally.
Single-phase WATER is assumed. With a steam pocket or flashing the behaviour changes completely and can be far more violent — steam-line hammer is outside this calculation.
Friction damping is neglected; on long lines the real peak is somewhat lower.

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Results are for engineering pre-assessment and are not a product selection commitment. Final responsibility rests with the user.