KEVOS® MAKEOS · Hydraulics
Valve Closure Surge (Water Hammer against Pipe Rating)
How big a pressure surge does closing this valve cause, does working pressure plus surge stay within the pipe rating, and how slowly must the valve close to keep it there?
Water-hammer check of a pipeline: pressure wave speed from the liquid bulk modulus and the pipe diameter, wall and modulus, the critical closure time 2L ÷ a, the Joukowsky surge for fast closure and the reduced surge for the closing time used (as the water hammer tool), working pressure plus surge against the pipe or component rating, and the slowest-needed closing time that keeps the total within the rating.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Change in flow velocity | m/s | Velocity change when the valve closes (the full flow velocity for a full closure). |
| Pipe length to the reflection point | m | Length of pipe from the valve to the tank or reservoir where the wave reflects. |
| Valve closing time | s | Time the valve takes to close. |
| Pipe inside diameter | mm | Inside diameter of the pipe. |
| Pipe wall thickness | mm | Wall thickness of the pipe. |
| Pipe elastic modulus | GPa | Elastic modulus of the pipe (about 200 steel, 1–3 plastics). |
| Liquid bulk modulus | GPa | Bulk modulus of the liquid (2.2 for water). |
| Liquid density | kg/m³ | Density of the liquid. |
| Working pressure | bar | Steady working pressure at the valve. |
| Pipe or component pressure rating | bar | Pressure rating of the weakest pipe, fitting or instrument. |
Method and formulas
- Wave speed a = √[(K ÷ ρ) ÷ (1 + K D ÷ (E t))].
- Critical time 2L ÷ a; Joukowsky surge Δp = ρ a Δv for closure within it; slower closure reduces it roughly in proportion, Δp × (2L ÷ a) ÷ t_c (as the water hammer tool).
- Closing time needed so working + surge ≤ rating: t = (2L ÷ a) × Δp_J ÷ (rating − working).
- Example: the wave travels at 1,314.9 m/s; closing in 1 s gives 7.984 bar surge, 13.984 bar in total against 16 bar.
Limitations
- Simple rigid-column estimate for a single pipe; networks and column separation need a transient analysis.
- Linear valve closure assumed; most valves cut flow mainly at the end of their stroke.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a pipeline for a fast-closing valve
- Set an actuator closing time
- Decide whether a surge vessel is needed
Who it is for
- Hydraulic engineers
- Plant engineers
- Maintenance engineers
What you get
- Wave speed and critical closure time
- Surge for fast and actual closure
- Total pressure against the rating and the closing time needed
Interpreting the result
- Slowing the last part of the valve stroke does most of the good: the flow changes fastest near closure.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 3024–3027. Topic reference; no source tables or recommended settings are reproduced.
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Open the Valve Closure Surge (Water Hammer against Pipe Rating) calculator
