How to install a water hammer on existing toilet plumbing

Written by emily patterson
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How to install a water hammer on existing toilet plumbing
Water hammer can occur from a rapid change in pressure when flushing a toilet. (red bathroom image by Jeffrey Sinnock from

Water hammer occurs when there is a rapid, large change in water pressure in the plumbing system. When a toilet is flushed, after the tank fills, the water valve closes very quickly and the pressure change in the pipes causes a loud banging noise in the plumbing. A special plumbing fixture, called a “water hammer arrester” contains a baffle of air that absorbs the shock of the water in the pipes and eliminates the water hammer sound caused by the change in pressure when the toilet valve closes quickly.

Skill level:

Things you need

  • Push-type water arrester fitting
  • Marker
  • Pipe cutter or hacksaw
  • Bucket
  • Old towels
  • Emery cloth

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  1. 1

    Turn off the water supply from the main water source.

  2. 2

    Locate the water line for the toilet closest to the supply line.

  3. 3

    Lay old towels on the floor to catch water that will leak from the pipe.

  4. 4

    Find a location on the water line where the water hammer arrester will fit with clearance for the baffle. Hold the water hammer arrester next to the section of pipe with adequate clearance. Use a marker to make a cutting mark on the water line that corresponds with the base of the fitting connections. Do not include the area where the pipes will seat into the fitting.

  5. 5

    Place a bucket on the floor under the section of pipe that will be cut. Cut the pipe on each mark with a pipe cutter or hacksaw. Raise the bucket after the first cut to catch the water as it drains out of the water line.

  6. 6

    Smooth any rough edges on the cut pipes with emery cloth.

  7. 7

    Align the water hammer arrester between the two sides of the water line. Press the pipes into the water hammer arrester fitting connections. Press firmly so the end of the pipe is as far as it can go into the fitting connection.

  8. 8

    Turn the water supply back on. Flush the toilet and listen for the banging noise. If it is gone, the project is complete. In some cases, a second water hammer arrester will need to be installed on the main water line.

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