Water hammer, also known as hydraulic shock or hydraulic surge, is a result of uneven or steady flow of water through pipes. It is best characterized as the clunking, thumping and banging sounds of a pipeline system once the piping system is turned off. If not handled properly or addressed, water hammer can be catastrophic and dangerous enough to rupture a pipe or damage adjoining flow control equipment over time. Many factors play a role in determining the severity of water hammer including the calculation of water hammer potential, application maintenance, and the correct selection of a check valve model for the appropriate application.
By Laura Jensen, Marketing and Communications Specialist, and contributing author Brian Allen, Engineering Manager – Flomatic Valves
How Does Water Hammer Occur?
When the flow of fluid is sharply stopped, a pressure wave is produced that travels through pipe systems. When fluid flows in a certain direction it creates momentum. When that momentum is suddenly obstructed, the fluid will rapidly try to return to its normal condition, causing the fluid to travel back through the pipe creating a shock wave. These pressure spikes, known as water hammer or hydraulic shock, are common among household plumbing and large industrial treatment plants; they can create enormous damage in a very short period of time.
The Effects of Water Hammer
The long-term impact of water hammer in a pipeline varies. The loud banging sound associated with water hammer is pressurized water slamming into a closed valve, plumbing joint, or other blockages, like a fluid pump. This repeated abuse from water pressure on valves and joints can seriously damage the pipeline system. Long-term effects of water hammer can also cause leaks on joint gaskets, pressure gauges, flow meters, and any other components associated with the pipeline system.
Cracked pipe walls and warped piping supports also result in costly repairs. Water hammer is also a safety concern. The extreme pressure can instantly blow out gaskets and explode pipes resulting in immediate danger to any person near the burst.
Water Hammer Calculations
Water Hammer Damage Prevention
Addressing water hammer issues starts with proper training and preparation when designing a pumping system. The first step is ensuring operators know the importance of slowly opening and closing shut-off valves. Engineers must also ensure that valves are placed in the correct locations of a pipeline system to reduce the potential of operator error. Pressure tanks and surge chambers can all be used to absorb hydraulic shock. Surge relief valves should also be considered.
Water Hammer Damage Prevention
Addressing water hammer issues starts with proper training and preparation when designing a pumping system. The first step is ensuring operators know the importance of slowly opening and closing shut-off valves. Engineers must also ensure that valves are placed in the correct locations of a pipeline system to reduce the potential of operator error. Pressure tanks and surge chambers can all be used to absorb hydraulic shock. Surge relief valves should also be considered.
Comprehensive Solution
Many factors play a role in determining the severity of a pressure surge within a pipeline system. Special consideration should be made to valve system applications with booster pump systems and water system plants that feature several manifold pumps, including long transmission lines, water well applications, or hot water closed systems. Doing this will help prevent the common issues that arise with water hammer.
To calculate water hammer, it is important to determine an approximate value using the simple formula: for every 1 foot/second flow of velocity change in a steel pipe, 54 PSI of pressure surge above the standard system pressure in the pipeline is generated. A more accurate calculation would be effective in systems with larger pump applications. Figure 1 reflects how surge pressure waves are generated based on the closing speed of a valve based on an example using 1,000 feet of transmission pipeline. When closing the valve in 1/2 second, 1,450 PSI is generated compared to closing the valve in 10 seconds when only a 120 PSI surge is produced.
It Is All About The Valves
Any check valve that relies on backflow to completely close is at higher risk for hydraulic shock.
When discs are pushed back onto the seat with too much force, it can damage the seal or change the alignment of the disc in the seat, causing leaking and failure.
Water hammer can be among the common issues of check valve failure due to the higher flow velocity. In addition, check valves such as swing check valves and double door check valves that close very slowly without any assistance can create hydraulic shock if not installed correctly or not properly selected.
Valves to Prevent Water Hammer
It is important to keep in mind that a properly engineered valve with the correct spring tension in place significantly reduces the chances of water hammer in any application. Check valves must close very fast when pumping fluid into a tank over a short distance. In these situations, it is important to use the equation noted in Figure 2 to determine the maximum surge pressure generated for the appropriate size and style of the valve.
Conclusion
The most common cause of water hammer occurs when there is a rapid change in water flow. As a result, these rapid fluctuations in water flow are often associated with the opening and closing of valves and the valves used in a piping system. As noted previously, solutions are available to stop hydraulic shock within a piping system, and it is never too early to prepare or prevent water hammer. Operators and engineers should always consider the fundamentals noted above in the design phase and commonly used styles to reduce water hammer in the long term for operators.
