This document discusses water hammer, which occurs when flowing water stops or starts quickly in pipes, causing pressure surges. It can cause pipe breaks, valve and pump damage, and contamination. Locations where water hammer often occurs include pump stations, control valves, isolation valves, hydrants during large demand changes, and air release valves. The document recommends using computer analysis to determine if a system has water hammer issues and recommends preventative measures like proper valve operation and selection of air valves and check valves to control pressure surges.

1. Understanding Water Hammer Ohio AWWA State Conference Presentation September 17, 2004 Dan Barr, PE

2. What Is Water Hammer?

3. What Is Water Hammer?

4. What Is Water Hammer? Webster says “ A concussion or sound of concussion of moving water against the sides of a containing pipe or vessel.” Also known as Surge Events or Fluid Transients

5. Valve Closure

6. System Dynamics of Valve Closure

7. Pump Start

8. Why Should I Care About Water Hammer?

9. Why Should I Care About Water Hammer? Service breaks Main breaks and flexible pipes versus rigid Plastic pipe has lower pressure rises but could fatigue and potentially fail at pressures under their rated capacity over time. Steel, Concrete, and Ductile Iron don’t expand as easily generating higher pressure rises, but lower fatigue problems. Contamination potential from negative pressures in mains Instrumentation and Gauge failures from extreme high or low pressures Control and Alarm issues – PRVs, Pressure based pump controls, etc.

10. Where and When Should I Be Concerned About Water Hammer? Anywhere flow stops or starts quickly Pump stations Control valves and isolation valves Hydrants Rapid and large demand changes Air release valves Column separation Longer Mains and higher velocities Networked mains less likely to have problems

11. Air Valve Caused Surge Air pocket

12. Air Valve Caused Surge Air is quickly expelled out of valve.

13. Air Valve Caused Surge Water hits valve and is immediately stopped.

14. Air Valve Caused Surge Secondary transient starts

15. Water Column Separation High point in main

16. Water Column Separation Low pressure wave arrives causing potential vacuum conditions

17. Water Column Separation High pressure wave arrives later and forces vacuum pocket closed

18. Water Column Separation Secondary transient wave started

19. Do I Have Problems with Water Hammer? How Can I Tell? Banging Noises and Vibration – Where term water hammer comes from Pressure waves bouncing off piping Check valve slamming Frequent pipe breaks in the same places especially near pump stations, etc or low or high points in the system. System measurements – normally transients are too fast for SCADA systems Potentially minimal symptoms due to infrequent occurrence or no monitoring

20. What Do I Do About It? Competent computer analysis to fully determine cause of problem or confirm no problem. Will also establish proper selection of any required corrective measures including locations, timing, and sizing. Preventive measures Valve operation including timing Pump starts/stops including delays, interlocking, and timing Proper check valve selection to prevent slamming Air valves

21. Air Valves: Controlled Column Rejoining a lot of air Low pressure wave hits and valve lets air in quickly to prevent vacuum.

22. Air Valves: Controlled Column Rejoining a little air High pressure wave arrives and tries to push out air. Small orifice prevents this and cushions the pressure wave.

23. Air Valves: Controlled Column Rejoining Water comes to a stop with no transient

24. What Do I Do About It? Control measures Surge control valves like pressure relief valves Surge and air tanks Pump bypasses Stronger system design

25. Questions and Answers