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How To Shield Irrigation Systems From Water Hammer

By David Olson on June 29, 2016 in Blog13 Comments

How To Shield Irrigation Systems From Water Hammer graphic

Water hammer. Surge. Dry line shock. These sound like spells cast by a wizard in a video game. But they’re actually names for a real event that can harm the irrigation systems you manage.

There is no silver bullet solution to totally prevent water hammer, but you can reduce the chances of it happening, and also mitigate its impact should water hammer appear in your system.

What is water hammer?
Water hammer can occur when you are opening or closing valves, or starting or stopping pumps. It’s the shock wave created by a surge of water, moving in empty pipes at a velocity of up to 5 feet per second, that stops abruptly inside the system. It’s like a bus driving at full speed into a wall.

The shock wave moves back through the system, rattling pipes as the energy in the water transfers to the pipes themselves, seeking relief. It will reach the valve with a loud bang or thump—hence the name water hammer.

Why worry about water hammer?
With the shock wave is an enormous spike in water pressure, or surge. This surge lasts less than a second, but it can do lasting harm to a system as each occurrence wears out pipe and loosens fittings. This will eventually cause leaks, and cost you time and money in repairs that could have been prevented.

What can you do about water hammer?
There is no magic cure for water hammer. But you can take steps to reduce its impact, and Ewing can help. Here’s how…

Clear the air to prevent water hammer from occurring
You can’t always stop air from entering the system. But you can carefully control how you expel the air from it to reduce dangerous velocities.

For example, when you turn on a system in the spring, first remove the furthest head on the line to allow air to bleed out. Then fill the pipes slowly with water from the main water valve to avoid trapping air.

Even the best-designed system can have air inside it. Air in the system can contribute to water hammer, as it can travel at a higher velocity than water. When the system is turned on, the water behind the air bubble will speed up, the air will run out of the system, and the result will be water hammer.

When a section valve is opened and the water travels unrestricted in the empty lateral pipes, it creates a shock. The air in the pipe will be quickly voided through the heads, causing those abnormal velocities that damage pipes, heads and component parts. This is called dry line (or dry pipe) shock.

Protect your system with air release valves. Air release valves open to release air when the system is turned off, and close up when water runs through the pipes. Install these valves on the high points of the system, where air collects, so air can bleed out through the valves and not blow out through the heads.

Air release valves are among the variety of specialty valves that your local Ewing store offers. Ask about options from Jain, Landscape Products and Christy’s.

Watts offers this water hammer arrestor.

A water hammer arrestor from Watts.

Cushion the blow when water hammer does occur
You have another option when it comes to diminishing the harmful effects of water hammer. Go to your local Ewing store and ask about the water hammer arrestor from Watts.

You can swiftly and easily install a water hammer arrestor in new or existing systems using a standard pipe tee. This device incorporates a pre-charged, permanent sealed air pocket to absorb potential shocks. Its piston is the only moving part, and it can recharge the air pocket.

If you’re not cautious about how you turn on a system, then the possibility of water hammer will still exist—the change in velocity happens too quickly for any prevention to start in time—but you can neutralize the shock with an arrestor.

Don’t get hammered
The surge in water pressure occurs in a matter of milliseconds, so it’s always too late to stop it once it’s begun. But by using caution when turning on a system, you can avoid a water hammer event. And by installing a water hammer arrestor and air release valves, you can defuse water hammer’s damaging effects and avoid costly (and preventable) repairs.

Your local Ewing store can share more maintenance solutions with you. Stop by today to learn more about how you can better protect and maintain your irrigation systems.

How To Shield Irrigation Systems From Water Hammer graphic
David Olson
Find your nearest Ewing location at EwingIrrigation.com/locations.

13 Responses to How To Shield Irrigation Systems From Water Hammer

  1. Stephanie Gieseler December 12, 2017 at 8:07 pm #

    Thanks for providing this information . No one in Hawaii seems to know how to cure the water hammer in our sprinkler system.

  2. Install auto drains or king drains on the mainline. If the water hammer is occurring in the lateral line install a SAM head at the lowest point in the zone. But most importantly turn the system on slow and if pressure is high, above 80psi install a PRV on the main line.

    • Mike March 11, 2019 at 10:29 pm #

      What do you mean by turning the system on slow? We have automatic valves that are controlled by three clock.

      • Laura Ory March 26, 2019 at 10:29 am #

        Hi Mike, this step applies if you winterized your system and closed the systems main water valve. This valve should be opened slowly to allow pipes to fill with water gradually. If they are opened too quickly, a pressure surge could cause uncontrolled flow, water hammer and damage.

  3. You can also install an outdoor hydrant and purge the system at start up in main line. If water hammer is consistent with the lateral line loop the line to control velocity of water.

  4. Linda May 13, 2020 at 10:50 am #

    If I hire a plumber to add the arrestor and the POV pressure reducing valve, what should I expect to pay.

    • Robyn Hazen August 4, 2020 at 9:30 am #

      Hi Linda – the cost is likely to vary depending on where you’re located. Your best bet is to visit your local Ewing branch who may know more. Here’s a link to our Locations page if that helps you find the branch closest to you: https://bit.ly/33oXjjN

  5. Joel January 1, 2021 at 10:13 am #

    i have just started to get this with my lawn sprinklers. could it be caused by the cold weather? temperature in the 30s? it has worked fine all through the summer and previous winters here in Phoenix? what do you think?

    • Robyn Hazen January 15, 2021 at 8:45 am #

      Hi Joel – Typically, cold weather by itself will not cause an irrigation system to be affected by water hammer. But if the system was winterized and all the water was purged with an air compressor prior to freezing conditions, and then it was not restarted properly by a process of systematically opening various valves and purging the air slowly until the water flows out of the sprinklers, then air trapped in the lines will cause the piping to rattle until enough air is evacuated from the waterlines. If there was no winterization performed, an intrusion of air from a water-break on the water line that is then not purged completely from the line, can also cause the water hammer/dry shock effect on a pvc water line. I hope that helps!

  6. Bob August 27, 2021 at 7:45 am #

    Hi. Where should the hammer arrestor be installed? After the back flow? On the mainline into the house?

    Thanks.

    • Robyn Hazen August 31, 2021 at 9:45 am #

      Hi Bob – I spoke with our team, and they explained that the device has to be installed on the mainline 3 or 4 feet before the irrigation valve that is producing the water hammer issues (noise or breaks). As the Water Hammer Arrestor is connected to the mainline and installed with a metal pipe, 2 feet above ground, it has to be protected from impacts that can break the connection to the mainline. If the water hammer effect is detected in other sections of the mainline, you can install another Water Hammer Arrestor; but keep in mind that the very first step to eliminate water hammer issues is to identify what is causing the problem. Sometimes you have water hammer issues after installing a booster pump in the irrigation system. Depending on the topography and mainline installation trajectory, you may have to install air relief valves (double effect valves) to eliminate the air from the mainlines. The air relief valves have to be installed at the highest points of the mainline.

  7. Tom Hudson November 23, 2021 at 10:59 am #

    I live in the Phoenix are and our sprinkling system is never turned off.
    We’ve experienced water hammer twice now, and both times it came from a broken off sprinkler head.

    The sound comes from inside a shed where a hose attaches.
    When it happened, I could turn the hose on and it would stop, but it returned when that sprinkler circuit came back on. I changed the broken riser and head and it stopped.

    Would it help if I installed an arrestor in the shed by the hose pipe?

    • Robyn Hazen November 30, 2021 at 8:03 am #

      Hi Tom – I spoke with our team, and they explained that there are several reasons for water hammer to occur. It’s often an easy problem to fix, but we need to know some details of the installation to identify what part or condition of the system is the origin of the issue. A member of our team will contact you at the email address you provided here. Thanks for reaching out!

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