What Is a Water Hammer Arrester?

Written by keith allen
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Water hammer is defined as the thumping sound made by water pipes when the flow of water is stopped. Think of it as the sound of the flowing water running into a closed valve. The force generated by the rapid stop of the water can cause pipes to shift while the sound reverberates through the house by the vibrations of the pipes. An arrester controls the violation and sound generated under these conditions.


A water hammer arrester is designed to absorb the energy of the moving water as it comes to a stop when the valve closes. Smaller arresters are designed for single- family homes while larger units would be used in commercial buildings or apartment complexes.


A water hammer arrester is made up of an air bladder and a spring. The device works similarly to an automotive shock absorber with the waterproof air bladder and spring absorbing the pressure spike.

Water Hammer Arrestors in Short Water Lines

Plumbing Supply.com suggests water hammer arresters should be installed near the end of a branch water line of less than 20 feet.

Water Hammer Arrestors in Long Water Lines

Branch lines longer than 20 feet require two arresters. Place one between the last two fixtures on the water line and another near the midpoint of the waterline.

Installing the Water Hammer Arrestors

Water hammer arresters are installed at a right angle to the branch water line. Depending on design and manufacturer the arrester may require solder installation. Follow manufacturer’s instructions for installation. There are also arresters designed to be attached to water lines by threaded couplers. These are often used in water lines in laundry rooms.

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