KEVOS® MAKEOS · Hydraulics
Water Hammer Pressure Surge
How big a pressure surge will closing this valve cause?
Pressure wave speed in a pipe, the Joukowsky surge for a fast valve closure, the critical closure time, and the reduced surge for slower closure.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Velocity change | m/s | Change in flow velocity caused by the valve (the full velocity for a complete closure). |
| Pipe length to the reservoir or open end | m | Length of pipe between the valve and the nearest reservoir, tank or open end. |
| Valve closing time | s | Time the valve takes to close. |
| Pipe inside diameter | mm | Inside diameter of the pipe. |
| Pipe wall thickness | mm | Pipe wall thickness. |
| Pipe elastic modulus | GPa | Elastic modulus of the pipe material (steel 200 GPa, PVC about 3 GPa). |
| Fluid bulk modulus | GPa | Bulk modulus of the liquid (water 2.2 GPa, hydraulic oil about 1.5 GPa). |
| Fluid density | kg/m³ | Liquid density. |
Method and formulas
- Wave speed a = √((K/ρ) ÷ (1 + K D ÷ (E t))).
- Fast closure (tc ≤ 2L/a): Δp = ρ a Δv.
- Slow closure: Δp ≈ ρ a Δv × (2L/a) ÷ tc.
- Example: stopping 2 m/s of water in a 100 mm steel pipe gives up to 26.245 bar.
Limitations
- Simple estimate; valve characteristics, column separation and branches need a transient analysis.
- Add the surge to the steady operating pressure.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check pipework for surge when a valve shuts
- Choose a valve closing time
- Decide whether surge protection is needed
Who it is for
- Process engineers
- Maintenance engineers
- Design engineers
What you get
- Wave speed
- Critical closure time
- Joukowsky surge
- Estimated surge for the actual closing time
Interpreting the result
- If the surge plus working pressure exceeds the pipe or component rating, slow the closure or add surge protection.
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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