How to Install a Water Hammer Arrester

A water hammer arrester is a plumbing device that protects your pipes from the damaging effects of water hammer. Water hammer occurs when a valve in your plumbing system suddenly closes, causing a pressure wave that can result in loud banging noises in your pipes. Over time, this can lead to leaks, cracked fittings and other damage. Installing a water hammer arrester absorbs these pressure waves, preventing the damaging effects.

What is a Water Hammer?

Water hammer, also known as hydraulic shock, occurs when a valve in your plumbing system suddenly closes or opens. Common causes include turning off a faucet or appliance valve quickly, flushing a toilet, or a washing machine or dishwasher valve opening or closing.

When this happens, the water flowing through the pipes is brought to an abrupt stop. However, the water maintains its inertia and momentum, which causes a pressure wave to surge through the pipes. This manifests as a loud banging or hammering noise.

The intense pressure from the wave can eventually cause pipes, fittings, valves and even welded or soldered joints to crack and leak over time. Water hammer arresters prevent this by absorbing the shock wave.

Why Install a Water Hammer Arrester?

There are several benefits to proactively installing water hammer arresters:

  • Prevent damage – By absorbing pressure waves, arresters prevent cracks, leaks and damage to valves and fittings caused by water hammer. This avoids costly repairs down the road.
  • Reduce noise – The arrester eliminates or muffles the loud banging noises caused by water hammer. This is especially important if you have plumbing running through walls near bedrooms or other living spaces.
  • Improve longevity – By protecting the plumbing system from damage related to water hammer, arresters help extend the overall life of the system.
  • Prevent disruption – Damage from water hammer can lead to leaks and even flooding. Arresters prevent leaks and disruption from broken pipes or fittings.

For a relatively low upfront cost, installing arresters throughout a plumbing system provides long-term protection and prevents headaches from water hammer damage. It’s a smart preventative measure.

Where are Water Hammer Arresters Installed?

Water hammer arresters are installed in strategic locations throughout your plumbing system to protect valves and sections of pipe most prone to water hammer. Some key locations include:

  • Washing machine shut off valves – The frequent opening and closing of wash machine inlet valves makes them very prone to water hammer. Installing arresters here prevents damage.
  • Dishwasher shut offs – Just like washing machines, dishwashers cause water hammer at their shut off valves, making arresters here a must.
  • Toilet supplies – Quick closing toilet fill valves cause water hammer when they close after refilling the tank. Arresters at the toilet supply lines prevent damage.
  • Faucets and shower valves – Any frequently-used faucet or shower valve in the system should be equipped with a water hammer arrester to avoid damage.
  • Sprinkler valves – Much like supply valves, the valves that operate irrigation and sprinkler systems are prone to water hammer and should have arresters.
  • Long pipe runs – Any sections of pipe with long, uninterrupted runs should have an arrester installed partway down to protect the entire line.

Installing arresters at water hammer prone locations provides comprehensive protection for the entire plumbing system.

Types of Water Hammer Arresters

There are two main types of arresters used to absorb water hammer pressure waves:

Air Chamber Arresters

Air chamber arresters consist of a short section of vertical pipe capped at both ends. The pipe contains an air pocket that compresses when the pressure wave hits, providing a cushion. These are best suited for low-pressure residential plumbing systems.

Piston Arresters

Piston arresters contain a piston sealed inside a cylinder with a spring. The spring-loaded piston moves in response to water hammer, absorbing the shock. These are used for high-pressure commercial plumbing systems.

Within these two types are a variety of sizes, valve configurations and installation options. Make sure to get the right style and size recommended for your specific application and plumbing system.

How to Install a Water Hammer Arrester

Installing a water hammer arrester to protect against water hammer involves a few simple steps. Here is a step-by-step overview of how to install an air chamber style arrester:

Step 1: Shut Off Water

The first step is to turn off the main water shut off valve for the building so supply is cut off to the pipes. This allows the system to be drained down so the arrester can be installed on empty pipes.

Step 2: Cut Into Line

Determine the proper location on the line to install the arrester, ideally on the vertical section of pipe. Cut out a short section of the pipe with a tube cutter. Make sure the remaining pipe ends are straight and free of burrs or debris.

Step 3: Install Fittings

Install compression or threaded fittings on the cut pipe ends to match up with the arrester connection size and type. Apply thread sealant to threaded fittings if needed.

Step 4: Install Arrester

Place the arrester between the fittings and hand tighten the connections. Then use a pipe wrench to give an additional quarter turn past hand tight. Don’t over tighten. The arrester should be installed vertically to function properly.

Step 5: Reopen Water Supply

Once the arrester is securely installed with leak-free connections, slowly reopen the main water valve. Check for any leaks and tighten fittings as needed. Allow air to bleed out of the line.

Step 6: Test Operation

Test the arrester by closing a valve downstream fast to simulate water hammer. The arrester should silence or muffle the noise if operating properly. Repeat for other locations as needed.

And that’s it! With a properly installed water hammer arrester in place, your plumbing system will be protected from damaging water hammer.

Recommended Water Hammer Arrester Sizes

Choosing the right size arrester for your application helps ensure optimal protection. Here are some general guidelines on sizing:

  • Washing machine supply lines – For washing machine shut offs, a 2-inch arrester is usually sufficient unless it’s a commercial machine.
  • Dishwasher supply lines – Dishwashers perform fine with a 2-inch arrester in most cases.
  • Toilet supply lines – Opt for a 2-inch arrester for a toilet water supply line.
  • Individual faucets – For bathroom or kitchen faucets choose a 0.5 to 1-inch mini arrester.
  • Full home protection – For whole house coverage, install 3/4″ to 1″ arresters on the hot and cold main lines.
  • Sprinkler valves – Size sprinkler system arresters based on the pipe diameter, matching the inner bore dimension.

Always refer to the manufacturer’s sizing recommendations based on flow rate and pipe diameter. Oversizing is better than undersizing arresters.

Installing Arresters on Washing Machine Hoses

Washing machines cause some of the most severe water hammer due to the solenoid valves. Installing arresters on the hot and cold supply hoses helps prevent damage. Here are the steps:

Turn Off Water Supply

Locate the hot and cold supply valves behind the washer and turn them off. Unscrew the supply hoses from the valves and washer inlet.

Install Arrester Fittings

Screw on a Y-valve or dual outlet fitting on each supply valve if not already present. Apply thread seal tape.

Attach Supply Hoses

Attach the hot and cold rubber supply hoses to the respective inlet ports on the Y-valve fittings. Use hose clamps for a tight, leak-free connection.

Install Arresters

Screw a 2-inch arrester into the open branch on each Y-valve. Position them vertically. Use thread sealant if needed.

Connect Hoses to Washer

Attach the supply hoses to the corresponding hot and cold inlet ports on the back of the washing machine.

Turn Water On

Slowly turn on both supply valves all the way. Check for leaks. The arresters are now installed and will protect the hoses.

With arresters installed on the washing machine supply lines, the system is protected from water hammer caused by the machine valves.

Installing an Arrester on a Toilet Supply Line

Toilets are another common source of water hammer. Installing an arrester on the toilet fill valve supply stops the slamming noise when the valve shuts off. Here is how to install one:

Shut Off Toilet Supply Valve

Locate the supply valve below the toilet tank and turn it off. Flush the toilet to empty the tank.

Disconnect Supply Line

Unscrew the supply line nut from the tank fill valve. Remove the supply line from the valve.

Install Y-Valve Fitting

Install a Y-valve on the toilet supply valve if one isn’t already present. Apply thread tape and tighten securely.

Connect Supply Line to Y-Valve

Attach the supply line to one side of the Y-valve fitting. Tighten the nut gently using pliers. Don’t over tighten.

Install Arrester on Y-Valve

Screw a 2-inch arrester into the open Y-valve port. Position it vertically. Snug it hand tight plus a quarter turn more.

Reconnect Supply Line

Reconnect the supply line to the fill valve in the toilet tank. Turn on the supply and test for leaks.

The arrester will now absorb the water hammer shock when the fill valve closes after refilling the tank. The toilet will refill more quietly.

Installing Arresters to an Entire Plumbing System

For full home protection, arresters can be installed on the main water supply lines. This protects against system-wide water hammer.

Shut Off Main Water Supply

Locate the main water shut off valve for the house, usually near the meter. Turn it off to depressurize the plumbing system.

Choose Install Locations

Select accessible locations on the vertical cold and hot water main lines to install the arresters, such as near laundry or utility areas.

Cut Into Each Line

Cut a short section out of each line using a tube cutter. Make clean, straight cuts on the existing pipes.

Install Threaded Fittings

Thread on union couplings, elbows, tees or other fittings that match the arrester connection size and type.

Install Arresters

Apply thread sealant if needed. Hand tighten the main line arresters into the fittings plus 1/4 turn. Position them vertically.

Turn Water Back On

Slowly turn the main valve back on once arresters are installed. Check for leaks and tighten if needed.

The entire system now has water hammer protection. Whole house arresters should be 3/4″ to 1″ sized models. Install one on both hot and cold lines.

Installing an Arrester for an Individual Faucet

For sinks prone to water hammer, mini arresters can be installed under the sink. Here is how:

Shut Off Water Under Sink

Locate the shut off valves for the faucet supply lines under the sink. Turn them both off before proceeding.

Disconnect Supply Lines

Unscrew the nuts connecting the supply lines to the faucet tailpieces (one hot and one cold).

Install Supply Tube Fittings

Thread a T-fitting onto each supply valve if not already present. Apply thread tape and tighten.

Reconnect Supply Lines

Reattach the supply lines to the ends of the T-fittings. Tighten gently with pliers.

Install Arresters

Screw a 0.5 or 0.75 inch mini arrester vertically into the remaining T-fitting ports.

Turn Water Back On

Open the shut off valves slowly. Check for leaks and tighten fittings as needed before testing operation.

The small arresters installed on the supply lines will help quiet water hammer caused by the faucet. Mini arresters may also be installed using push-fit connections instead of threaded if desired.

Troubleshooting Water Hammer Arresters

Water hammer arresters are generally reliable and don’t require maintenance. But here are some steps to take if yours stops working:

  • Inspect for leaks – Tighten any leaking fittings on the arrester. Leaks indicate it is not properly absorbing water hammer.
  • Check flow direction – The arrester must be installed vertically to function. Water should flow in and out the bottom.
  • Ensure full closure – Valves the arrester is connected to must close fully to create water hammer. Adjust if needed.
  • Replace worn gaskets – Worn or dried out internal gaskets prevent the arrester from sealing properly to absorb shock waves. Install new o-rings or gaskets.
  • Flush debris – Debris, sand or scale inside the arrester can impair operation. Disconnect and flush clean with water.
  • Drain air chambers – Arresters may need bled if water displaces air over time. Disconnect and allow to refill with air.

If problems persist, the entire arrester may need replacement if worn out or improperly sized.

Professional Installation

While installing basic water hammer arresters is a project a knowledgeable DIYer can tackle, you may want to consider hiring a professional plumber for larger jobs or complex systems.

The benefits of professional arrester installation include:

  • Proper sizing – They will spec arresters of the right size based on pipe diameter and water demands.
  • Code compliance – A licensed pro will ensure all work complies with plumbing codes. Permits may be required.
  • Whole home protection – They can install multiple arresters throughout your plumbing system for comprehensive protection.
  • Fixing leaks or damage – Any leaks or damage from existing water hammer can be repaired.
  • Adjusting water pressure – Excessive water pressure makes water hammer worse. A plumber can regulate pressure.

While a bigger investment upfront, hiring a qualified plumber ensures your system is protected from water hammer by properly installed and sized arresters.


Installing water hammer arresters is an important preventative measure to protect your plumbing from damage and nuisance water hammer noise. By absorbing pressure shock waves, arresters prevent leaks, cracks and broken pipes or fittings. They are simple devices that install on water lines prone to water hammer issues. Sizing the arresters properly and installing them in the right locations provides comprehensive protection for your plumbing system and fixtures. With arresters in place, you can rest easy knowing your plumbing system is shielded from the destructive effects of water hammer.

How to Install a Water Hammer Arrester: FAQ

Installing water hammer arresters is an effective way to prevent damage and noise from hydraulic shock in your plumbing system. Here are answers to some frequently asked questions about installing these helpful devices:

How do I know if I need a water hammer arrester?

If you hear loud banging noises when turning water off or on rapidly, it is a sign you need arresters. Damage like leaks or cracks from water hammer also indicate arresters should be installed.

Where should water hammer arresters be installed?

Arresters should be installed near quick-closing valves and appliances like washing machines, dishwashers and toilets. They can also be installed on long pipe runs. Putting them near the source of the water hammer is most effective.

What size arrester should I use?

The arrester must be sized appropriately for the pipe diameter it is installed on. Check manufacturer specifications based on the pipe size. Standard residential sizes are often 3/4″ or 1″ models.

How do I install an arrester on a washing machine?

Use Y-valves with the supply hoses to allow installation of arresters on both hot and cold lines. This protects from machine solenoid valve water hammer.

Can I install arresters myself?

In many cases, DIYers can install arresters on accessible water lines. Whole home installation or work on complex plumbing may require a professional plumber.

How can I tell if my arrester is working properly?

Check for leaks around the arrester fittings. The absence of water hammer noises when valves close rapidly also indicates proper operation.

What should I do if my arrester starts leaking?

Tighten any loose fittings. If leaks persist, internal gaskets may need replacing. In some cases, the entire arrester requires replacement if worn out.

Where can I buy water hammer arresters?

Plumbing supply stores and major hardware stores typically carry a selection of water hammer arresters in different styles and sizes.

Do arresters require regular maintenance?

Water hammer arresters are generally maintenance-free. Occasionally air chambers may need drained and refilled if water seeps in over time.

Installing water hammer arresters is an easy, cost-effective way to protect your plumbing and eliminate annoying pipe noises. Positioning them strategically can provide whole-system protection.