More often than not, major water hammer problems are caused by a system component, like a sudden valve closure. However, due to the high wave speeds, water hammer surge waves will travel through the system at very high speeds which means that surge issues will exist well beyond the original source.
Due to the ’cause and effect’ nature of water hammer, it is best practice to tackle mitigation using a system approach and focus on the entire piping network. Focusing solely on your components will never reveal the interactions across multiple parts of your system.
Water hammer is rarely ever going to be JUST a check valve that’s causing an issue.
If you’re seeing a water hammer phenomenon, and maybe it’s a check valve slamming issue, look for what’s going on in the rest of the system. Because even though it may be a problem that’s happening here in one area, the pressure waves pass through the rest of the system very, very quickly. The moral of the story is when you’re doing a water hammer analysis, don’t just do a component approach.
It is very important to take a system approach to see what’s going on throughout the entire piping network. There is a cause and effect happening within your system where an event happens in a particular device that causes other potential failures in other areas as well. Don’t simply focus on the result, find the root cause.
Start with the valve closure you know about and then try other things.
If you have check valves, try seeing if you can allow the check valves to chatter a little bit less than instantaneously. Then, try a scenario where you change the way a valve closes; so in an emergency failure operation, you don’t want that particular valve to close fast or linearly. Maybe try to close the valve a different way to help dampen the surge. Just a warning, it’s not good to allow your pumps to deadhead against closed valves, so you might consider doing a pump trip as well.
Last but not least, if you need to try other surge mitigation methods using additional surge equipment such as relief valves, vacuum breaker valves, gas accumulators, surge tanks, etc. Each of those has a different function depending on the scenario you’re trying to model, and you can simply continue stepping your way through the analysis piece by piece. It’s very important that you use analysis copies (called child scenarios), and not apply all the changes all at once.
Make one change, review your graph animations to see what the effect is, and then try the next thing, and the next thing, and the next thing… It’s a slow step change through the process to analyze what’s going on in the entire system so you can prevent failure.
Mitigate Surge in Piping Systems Using a System Approach
The below webinar uses a cooling water example. Watch this surge analysis demonstration and see the potential failure areas beyond the initial cause of surge. Apply the technique to your analysis.Watch the Video
About AFT Impulse
Using AFT Impulse™, and its’ animation capabilities, engineers can address the source of surge and see test results side by side.
See graph results such as:
• Output data such as plot flows, pressures, velocities, and more vs. time
• Both instantaneous flow and integrated flow plots
• Custom graph formats
• Animated graphs dynamically display results for one or multiple flow paths