How to Install a Water Hammer Arrestor to Stop Banging Pipes

The first step is to confirm the source of the water hammer. Operate fixtures one at a time, such as flushing toilets, running the dishwasher, and starting the washing machine. Listen for the distinct banging or knocking sound that occurs when the water flow is abruptly shut off by a valve. In our assumed scenario, the washing machine's fast-acting solenoid valves are the culprits. You will need to install an arrestor on both the hot and cold water supply lines leading to the machine for the best results.

Before starting any work, shut off the water to the entire house. Locate your main water shutoff valve, which is typically found in a basement, crawl space, or utility room near where the water service enters the house. Turn the valve handle clockwise until it is fully closed. Next, relieve the pressure in the pipes by opening a faucet at the highest point of your house (like a second-floor shower) and the lowest point (like a basement utility sink). Let the water drain out until it stops. Place a bucket and have some towels ready under the section of pipe you will be working on to catch any residual water.

To install the T-fitting, you must remove a small section of the existing pipe. Take your push-to-connect T-fitting and measure its length from end to end. Precisely mark this measurement on the 1/2 inch copper pipe near the washing machine's shutoff valve. Attach a tubing cutter to one of your marks, tighten the knob until the cutting wheel makes contact, and rotate it around the pipe. With each full rotation, tighten the knob slightly. Continue this process until the pipe is cleanly severed. Repeat for the second mark. A clean, square cut is crucial for a leak-proof seal.

After cutting, the pipe ends will have sharp edges and small burrs. These must be removed to prevent them from slicing the O-ring inside the push-to-connect fitting, which would cause a leak. Use a deburring tool to ream the inside edge and smooth the outside edge of both cut ends of the copper pipe. Once smooth, use a clean cloth to thoroughly wipe the ends of the pipes, removing any copper filings, dust, or oils.

First, prepare the arrestor assembly. Wrap the male threads of the water hammer arrestor with 3-4 layers of Teflon tape, wrapping in the same clockwise direction that you will tighten it. Screw the arrestor into the threaded port of the push-to-connect T-fitting and hand-tighten. Use an adjustable wrench to give it a final quarter-turn to snug it up. Now, take the entire T-fitting assembly and push one end firmly onto one of the cleaned copper pipes until it bottoms out. You may hear or feel a 'click'. Then, align and push the other end of the T-fitting onto the other pipe end. Ensure both sides are pushed on completely. Repeat this entire process for the second water line (e.g., the hot water line for the washing machine).

With the installation complete, it's time to test your work. First, ensure all the faucets you opened to drain the system are now closed. Go back to the main water shutoff valve. Turn the handle counter-clockwise VERY SLOWLY. You should hear the pipes filling with water. Opening the valve slowly prevents a sudden pressure surge that could damage your plumbing. Once the valve is fully open, return to your work area. Carefully inspect the new fittings on all sides for any signs of dripping or moisture. Use a dry paper towel to wipe the connections and see if any wetness appears, which would indicate a very slow leak.

The final step is to confirm the problem is solved. Go to the appliance that was causing the issue—in this case, the washing machine. Start a wash cycle that uses both hot and cold water. Pay close attention during the fill cycle when the water valves will snap shut. The loud, sharp banging noise should be eliminated or significantly reduced to a very quiet thud. If the arrestors have worked, the hydraulic shock is now being absorbed by the air cushion within them. Your pipes are now protected from the damaging effects of water hammer.