Why Do My Pipes Start Knocking When The Sprinklers Come On?

Your sprinklers come on, spraying water droplets over your lawn. They come on routinely, ensuring your yard remains a luscious, green expanse. However, each time the sprinklers cycle on to do their job, your pipes begin making noise. They start knocking, creating a racket that disturbs your home.

Key Points:

  • Pipes may start making a racket when sprinklers cycle on and off due to water hammer.
  • Symptoms of water hammer include noises from valves, pumps, and repetitive knocks or thumps.
  • Possible fixes include removing air from the system or increasing water velocity.

Since this impromptu concert isn’t particularly wanted, you’ll need to get to the root of the problem before fixing it. So, what causes your pipes to start knocking when your sprinklers come on? While unveiling the culprit usually reveals water hammer, it can result from other issues. This article explains the potential causes and how to fix them, so stick around to learn more!

What Causes Knocking Pipes When The Sprinklers Come On?

Water hammer is the most common culprit behind a knocking noise from your pipes when the sprinklers come on. While the problem can result from other issues, like high water pressure, issues with the sprinkler head, or air in the system, water hammer is a common culprit with sprinkler systems.

The issue often lies with the valve controlling water flow to the irrigation system. If you have an automatic valve on your irrigation system, you might notice a knocking sound when the sprinklers cycle on and off. This can happen due to the sprinkler valve opening or closing too fast, causing the water to suddenly change direction and speed, resulting in a knocking sound.

What Is Water Hammer?

Water hammer is a phenomenon that plagues countless piping systems. This issue can occur in any piping system that utilizes valves to regulate the movement of liquids or steam through the system, including your irrigation system.

The phenomenon, also known as hydraulic shock, occurs when the valve on a high-pressure system abruptly closes. When the shut-off valve shuts, it abruptly halts the momentum of the liquid flowing throw the pipe. This causes a pressure wave that resonates through the fluid inside the system, causing it to undergo substantial force.

The once-moving water suddenly changes speed, resulting in a shockwave. The hydraulic shock travels throughout the pipeline, causing the noisy knocking sound you hear.

How Do I Know If Water Hammer Is Causing The Issue?

When water hammer is the culprit behind the knocking sound, you’ll notice a few key signs. These signs often include:

  • Noises when the valve opens or closes
  • Noises when the pump starts
  • Loud, repetitive knocks or thumps followed by silence

However, many folks often write off noises from their pipes as water hammer, even if the noise doesn’t match signs of it. Multiple factors can cause noise from your water system, including an undersized water meter supplying your system, water pressure higher than 60 PSI, or valve issues.

So, if the noises emanating from the pipes don’t match the signs of water hammer, it’s time to start considering other potential culprits.

How Do I Stop My Sprinkler System From Water Hammering?

If the pipes in your home start knocking when your sprinkler system comes on, there are a few things you can do. The correct fix depends on the root cause, so work your way through the following methods. Sometimes, the issue may present itself as water hammer but stem from something else, so an alternative approach might be necessary.

Remove Air From The System

In some cases, pockets of air in your plumbing system can aggravate the symptoms of water hammer, making it seem even worse. In most cases, the plumbing system in residential homes is equipped with a vertical pipe among the lateral pipes near the water valve. This pipe is full of air and functions as a cushion to absorb the hydraulic shock when the valve closes.

However, if the valve becomes waterlogged, it can’t do its job correctly, resulting in the water hammer issue. So, to correct the problem, you need to drain your system to allow air into the chamber. Alternatively, you can increase the water velocity to correct the issue, but you may find it easier to drain the system.

Do this by turning off the water at the main shut-off valve, then open all of the faucets in your home, starting with the highest faucet (on a second floor, if applicable). Continue opening the faucets in your home, moving down to the lowest floor (basement or first floor).

Once you drain the entire system and water stops flowing from the faucets, the air chamber should refill with air instead of water. So, after the taps stop flowing, turn the water back on at the main shut-off valve.

Install A Water Hammer Arrestor

Removing air from the system might not always do the trick, so the next step is to install a water hammer arrestor. These devices utilize air-filled cylinders that aid in water hammer prevention by absorbing the shockwave from sudden water pressure increases when the valve turns off.

Most of these devices feature a generic design and are easy to install with screw-type connectors that easily thread onto the supply line and shut off valve. While the installation process is relatively simple, you’ll need to choose the right location for the device.

Check with a plumber if you’re unsure of the best placement to prevent water hammer due to your irrigation system. They can handle the installation for you, ensuring it’s installed correctly at the proper place.

Check The Water Pressure

Excessively high water pressure can contribute to water hammer symptoms, so if you install a water hammer arrestor and the problem persists, check the water pressure. You can easily check the water pressure in your home with a simple pressure gauge, which you can buy at home improvement stores.

Some homes feature dedicated pressure gauges, so if your home has one, use it instead of a pressure gauge. Ideally, you should use the water source closest to where the main supply line enters your home. This will ensure the most accurate reading, so select the faucet or fixture closest to this area. Choose an outdoor spigot or an indoor faucet that sits near the entry point. Simply attach the gauge to the hose bib or faucet and turn on the tap for a reading.

When you test the water pressure, ensure there aren’t any other fixtures in your home consuming water. This includes washing machines, showers, toilets, refrigerators with ice makers, sprinklers, and dishwashers. If any other fixtures are actively pulling water, it could result in a false low reading.

For the most part, residential water pressure ranges between 40 and 50 PSI. Many standard pressure regulators feature a maximum adjustment of 75 PSI, but most residential water systems shouldn’t exceed 60 PSI. If they do, the excessive water pressure could be causing the water hammer issue.

If your home has an abnormally high reading, check with a plumber. You will likely need to install a pressure regulator to avoid damage to the system if you don’t already have one.

Stabilize Loose Pipes

Sometimes, loose pipes throughout your home can cause the knocking sound often associated with water hammer. The abrupt changes in the speed and direction of water flowing in your home can jostle the pipes, causing them to bump against your home’s framing and other structures, like drywall, floor joists, and ceilings.

So, if you’ve checked everything else and it appears fine, ensure loose pipes aren’t the problem. You’ll need to isolate where the knocking noise is coming from. For example, if you notice the knocking sound under your sink when the sprinklers come on, start there.

Check the pipes and ensure the mounting straps are adequately secured, as this will prevent them from jostling around when water moves through them.

Call A Plumber

If you have tried everything you can think of, but the pipes in your home continue to make noise when the sprinklers come on, it might be time to seek professional help. They can help you troubleshoot the problem and isolate the culprit to ensure the pipes in your home don’t make a racket every time your sprinkler system turns on.

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