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Causes of Water Hammer and How to Fix It


Why water hammer happens in an irrigation system and details on how you can fix it. Read on for more information.

August 15, 2021

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Causes of Water Hammer and How to Fix It


Water hammer can be a very loud, persistent problem. It’s recommended to determine the source of the noise before starting any work.

Water hammer is caused by an increase in pressure within water systems. A form of hydraulic shock, energy transformed into surge pressure produces a shock wave from a sudden change or stop in flow that spreads through the system and creates pounding noises within the pipes. The larger the changes in velocity, the greater the pressure. This can be caused by valve operation, starting and stopping pumps, directional changes from pipe fittings, heavy mineral buildup and rust inside shut off valves, air in pipes, or too much water in an air chamber.

It’s imperative to catch water hammer quickly, as it can cause costly damage.


Probable Sources

There are many different causes of water hammer. If new work is completed, it could be caused by poorly secured pipework. Wear of certain valve types, such as ball and float valves, fast acting valves, and worn stop valves can potentially create issues as can design errors. Lastly, trapped air within a system can build up pressure, leading to water hammer also.


Potential Damage

Water hammer can inflict a wide range of problems, including damage to pumps, valves, instruments, and failure of joints. The integrity of pipe walls and welded joints can be compromised. Leaks are common with water hammer and can damage other equipment, increase in intensity, and are easily missed early. It can also rupture pipes and cause system failure if not fixed in a timely manner. External property damage is also something to be wary of with water hammer, as leaks and ruptured pipes can lead to washouts, property damage, or slip and fall accidents.


Methods to Fix Water Hammer

Because of the numerous system designs there is not a one-size-fits-all water hammer fix. Check your customer’s system to determine where the water hammer is occurring, then plan based on their system.

Reduce System Pressure
If they’re noticing water hammer in their irrigation system, try lowering the system pressure. This reduces water demand for the sprinklers, reducing velocity in the pipes and therefore reducing water hammer. While this will reduce the overall surge pressure, it doesn’t eliminate it. To do this, turn the main shut-off valve of the sprinkler system to 50%, then run the system. Close the valve incrementally until the water hammer goes away. Ensure the sprinklers are still running effectively and emitting water the proper distance. If the sprinklers are not running well or not spraying water far enough, you will need to try another solution.

However, if the irrigation system works, test and see if there are any other issues in your customer’s house due to the change in demand from the irrigation system. If all is well, install an adjustable pressure reducing valve after the shut-off valve you partially closed. Note that shut-off valves should not be left partially closed long-term, so be sure that you have all parts necessary for the job. Once done, open the shut-off valve fully and adjust the pressure reducing valve until the pressure works well for the irrigation system, but is low enough to prevent water hammer. This valve will compensate for the changes in water pressure.

If one valve zone of the sprinkler system creates water hammer, try incrementally closing the flow control stem on the irrigation control valve. If this stops the water hammer, you can leave this partially closed permanently.

Reduce Zone Run Order
With an automated irrigation system, try changing the order in which the valves run. Find the valve that uses the least amount of water (usually the one with the fewest sprinklers) and rewire the controller to run that valve last. Because water hammer is related to water flow, the valve with the least amount of flow is less likely to cause it when the valve closes.

Split Valve Zones
If an irrigation valve is causing the water hammer, split the valve zones. Reducing the number of sprinkler heads that the valve operates reduces the water velocity. Install a second valve and connect half of the sprinklers from the old valve to the new valve. Before trenching and installing pipe, be sure to run a check to see if this solution fits the system’s needs. Remove and cap off sprinkler heads and turn the valve off and on a few times to check for water hammer. Ideally, this should be done at the time water hammer is most prevalent in the system. If the water hammer disappears, ensure the second valve you install has the same number of sprinklers or fewer than the original.

If there is water hammer coming through multiple valves, you can split the valves with problems into two valve zones or you can install new, larger piping for the system. Check all piping from the water main to the valves to see if there is a section of pipe smaller than the rest. If found, replace that piping with a pipe double the original size to ensure lower velocity flow. If there’s not a section of smaller pipe, you may need to redo all the irrigation piping. Test install the new pipe before digging by running it aboveground first to see if the new pipe stops the water hammer.




Methods of Prevention

Replace or install piping with air chambers. Air chambers are a short pipe segment with an empty air chamber that serves as a shock absorber for water to expend after sudden directional changes.

Flush old systems. Stale, sitting water can have sediment sitting in it, especially if there is a lower flow. It takes very little debris to create a valve failure or stop up drip emitters, misters, and bubblers; sand is a major culprit of ruining new systems quickly. Ensure you’re flushing the system over a long enough period to wash out all the debris.

A pressure regulator and pressure reducer can be installed as well to reduce operating pressure.

Stay Alert. Prevention and quick action are key with water hammer issues. Keep an eye and ear out on the job to save your customers from costly damage. Visit SiteOne.com/irrigation today to find the tools and support you need for the job.