What Are Water Hammer Arrestors?

Does your plumbing bang and clang like a truckload of scrap metal? If so, your pipes may be suffering from “water hammer.” The cure for this condition is a water hammer arrestor, an inexpensive device that can often be installed in a single afternoon.

I spoke with a trio of licensed plumbers to learn what causes water hammering, why it’s a serious issue, and how water hammer arrestors can solve the problem.

What Is Water Hammer?

Water moves through your pipes fast. Turn your kitchen faucet on full blast to get a feel for just how fast it moves. When it’s flowing and then is abruptly shut off, the water’s momentum slams into the end of the pipe, causing it to hammer against the hangers and wooden framing it touches.

The result can be a shocking level of rattling and banging, explains master plumber Aaron Adams. “Water hammering is very loud and causes pipes to shake violently. Other times homeowners may hear loud intermittent bangs when they turn water on and off in certain parts of the home.”

What Are Water Hammer Arrestors and How Do They Work?

TMB STUDIO

A water hammer arrestor provides an off-ramp for the water’s momentum, like the emergency off-ramps on mountain highways, where trucks can safely divert if they get too much speed on a steep downward slope.

Arrestors have a piston or diaphragm separating the water line from an air-filled chamber. When the water’s momentum is high enough, the piston becomes the path of least resistance. The water pressure pushes the piston into the air on the other side, which compresses, absorbing and dispersing the water’s momentum.

This current design is an upgrade over old-school “air chambers” found in older homes. Air chambers were essentially arrestors without the piston. Over time, however, they filled up with water, making them ineffective.

Shaylin King, a licensed plumber with Mr. Rooter, compares water hammer arrestors to shock absorbers for your plumbing. “While not always necessary,” says King, “especially if your plumbing is properly sized and secured, they’re a smart preventative measure in many homes to protect against sudden pressure surges and potential pipe bursts.”

Why Are Water Hammer Arrestors Important?

Depending on the volume, water hammering can be mildly annoying or highly alarming. But the noise is only the symptom. The real issue is that the forces involved can damage the pipes, potentially resulting in breaks and leaks.

The most obvious issue that arrestors solve is that annoying water hammer rattle. But that noisy rattle is the side effect of the real problem: water slamming at full speed into the pipe junction. Over time that force can shake pipes loose from hangers, making the noise even worse, or even shake fitting loose can cause leaks.

“Plumbing pipes are not designed to withstand shaking or movement,” explains Adams. And that shaking, over time, can cause connections to come apart, or even wear holes through the pipes.

What Appliances Need Water Hammer Arrestors?

Before you install a water hammer arrestor, determine which faucets or valves in your house cause the noise. Washing machines and dishwashers are prime suspects because their automatic valves close fast.

Of course, not every appliance needs a water hammer arrestor. If the appliance cuts off water gradually enough, the change in momentum is minimal. If you’re not suffering from water hammer, then you don’t need to worry about it.

How Much Does It Cost to Install Water Hammer Arrestors?

A water hammer arrestor costs from $15 to $50. They’re available online, at home centers, and in hardware stores. Most of the cost of a water hammer arrestor installation is in the labor.

Calling in a pro will typically run $250 – $500. Shaylin King explains that the price largely depends on the placement within your plumbing system, since an arrestor install sometimes requires opening walls to access the end of pipe runs. In cases like that, where the plumbing is difficult to access or will require drywall removal and repair, the cost can balloon up as high as $1,000.

Clearly, this is an area where a DIY installation can save a great deal of money. But it’s important to do things right. As Aaron Adams points out, “cutting corners to save dollars in plumbing can lead to nightmares for homeowners.”

How to Install Water Hammer Arrestors Yourself

Arrestors are available for every type of pipe. The exact tools you’ll need will depend on what type of pipe you’re working with, and where you’re installing the arrestor. You may need to cut into the pipe, or you may be able to install a threaded connection. They’re typically installed at the end of a water line near the plumbing fixture that’s causing the hammering. If that’s not enough to eliminate the water hammering, Shalyn King suggests installing them at any 90-degree turns.

Once you pick a location, there’s a great deal of latitude about how the arrestor is installed.

“Generally, there is no ‘upside-down’ for a water hammer arrestor,” says Adams. “Arrestors are effective when installed vertically (in either direction), horizontally or at an angle.” But that’s not true of all models, so always check the manufacturer’s instructions.

You may want to coordinate a water hammer arrestor install with other work. Destry Thompson, of John Stevenson Plumbing, suggests installing them “in conjunction with a thermal expansion tank for your water heater to relieve excess pressure in the plumbing system.”

Personally, when installing an arrestor on older washing machines I like to take a moment to evaluate the shut-off valve itself. If the valve needs to be replaced soon, I’ll upgrade to new valves with integrated arrestors.

King had one more tip: give some thought to what access you’ll need down the road and install arrestors in areas you’ll be able to access when it’s time for a replacement. And that brings us to our next topic: replacing older arrestors.

How Often to Replace Water Hammer Arrestors

Luckily, water hammer arrestors don’t need to be replaced all that often. “Their lifespan is fairly long considering the forces they encounter,” says Adams. That said, every plumber I spoke to agreed that water hammer arrestors have a limited lifespan.

“Similar to a car’s shock absorbers, water hammer arrestors do wear out and eventually need replacing,” says King,

Where the pros disagreed was on how long they typically last. I heard estimates ranging from 5 to 25 years. Why so much variety? Because arrestor lifespan depends on a number of factors.

“Hammer arrestors can wear out depending on water quality, age, and pressure of the plumbing system,” says Thompson.

Another factor is how frequently the arrestors are used. If your arrestor is on a washing machine supply line, for example, there’s a dramatic difference in wear and tear if you wash a load of laundry every other day compared to once a week.

You’ll know it’s time to replace the arrestor if it shows signs of leaking or if the water hammering noises return.

FAQs

Do water hammer arrestors wear out?

Water hammer arrestors do wear out over time. Aaron Adams suggests occasionally checking arrestors for leaks at their connections to stay ahead of any problems caused by aging.

Can water hammer arrestors be installed upside down?

This depends on the specific arrestor. Most – but not all! – can be installed in any direction. It’s important to check your specific model’s instructions for the manufacturer’s guidance.

About the Experts

Aaron Adams is a Master Plumber and CEO of Aaron Services: Plumbing, Heating, Cooling, a family-owned company serving the Atlanta Metro area since 1978.

Shaylin King is a licensed plumber with Mr. Rooter Plumbing of Tri-Cities, Yakima, and Hermiston, Oregon.

Destry Thompson has been in the plumbing industry for nearly 9 years, and is currently the General Manager of John Stevenson Plumbing.