How to Install an Air Chamber Under the Sink to Eliminate Hammering

Turn the whole house water supply shutoff valve to the “off” position. The shutoff valve is often located between the outside water meter and the house

Open both sink faucets to relieve any water pressure in the plumbing and place a container beneath the shutoff valves under the sink to catch any remaining water leaking from the pipes.

Grip the cold water shutoff valve with a pair of channel pliers and undo the supply hose compression fitting with an adjustable wrench.

Remove the cold water shutoff valve from the water supply pipe by turning it counterclockwise with channel pliers.

Place a pipe cutter over the cold water supply pipe protruding from the wall. Slide the tool sideways until the cutting wheel lines up with the start of the threaded section on the pipe. Tighten the knurled handle on the pipe cutter progressively while rotating the tool clockwise around the pipe to cut off the end threaded section.

Remove any debris from an inch long section on the end of the pipe by scouring it with a strip of emery cloth. Mark the pipe an inch from the end with a felt pen and insert one of the parallel ends of a 1/2-inch push-fit T coupling onto the pipe with the T leg facing upward. Press the fitting inward until you feel it lock into place and the end of the coupling lines up with the mark on the pipe.

Measure the distance from the upward facing leg of the T to the underside of the countertop with a steel measuring tape. Subtract 1 1/2 inches and transfer the measurement to a section of 1/2-inch copper pipe. Cut the pipe to size with the pipe cutter; ensure that both ends of the pipe are perfectly square.

Mark a point an inch from both ends of the pipe. Place a push-fit end stop over one end and press it home until the edge of the end stop lines up with the mark and you feel the fitting click into place.

Insert the other end of the pipe into the upward facing leg of the push-fit T coupling and press it home as described above. Place a spirit level against the vertical pipe and twist the T coupling either way until the spirit level bubble is centered.

Cut off a 2 1/2-inch length of 1/2-inch copper pipe and mark a point an inch from both ends. Insert one end of the pipe into a 1/2-inch threaded male push-fit straight connector and the other end into the remaining parallel leg of the T coupling. Grasp the T coupling and push the end stop inward until you feel both the end stop and the T connector lock into place.

Thread the faucet supply hose compression fitting onto the push-fit straight connector. Snug the fitting down and tighten it another quarter turn with the adjustable wrench.

Open the cold water faucet slightly to release trapped air in the plumbing and open both the cold water faucet shutoff valve and the main household shutoff valve. Close the faucet when air stops hissing out and check the installation for leaks; tighten the faucet supply compression fitting another quarter turn if necessary.

Open the cold water faucet fully and shut it as quickly as you can. Do this several times and repeat the exercise with the hot water faucet. If you still detect some water hammer, install a second air chamber onto the hot water side of the under-sink plumbing as described in Steps 3 through 12.