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Why Does My Washing Machine Shake My Plumbing?

Q: Why is my washing machine shaking my plumbing?

A: A washing machine usually offers years of trouble-free service. Now and then, however problems can arise. In most cases, the trouble with a washing machine is mechanical and isn’t related to the plumbing at all. However, the washing machine does tie into your home’s plumbing, and a few plumbing problems can occur.

You may notice that your washing machine rattles your plumbing, especially when it closes its valves. This noise can be loud, and is often referred to as “water hammer.” You can experience water hammer when you close a regular tap, but most often, you’ll hear water hammer from a washing machine or dishwasher.

A device called a solenoid controls washing machine valves. The solenoid acts like a mechanical “finger” and its job is to push a button or mechanically activate a device. In the case of your washing machine, the solenoid’s job is to shut the washing machine’s valves down as fast as possible, once the correct water level has been reached.

The valve has to move in opposition to the water pressure in your pipes. The pipe that feeds your washer may have over 80 pounds of water flowing in it, and the solenoid needs to stop that water in a hurry! Getting a good, clean shutoff takes some effort to overcome the fast-flowing water. The solenoid, which is an electromechanical device, slams the valve shut to prevent overflow. The sheer weight of the water in the pipe coming to an abrupt halt shakes your pipes; the momentum of the water has to be absorbed somewhere, and your pipes take the hit, sometimes making a great deal of noise in the process.

As you can imagine, over time the stress of water hammer can cause damage to your pipes. The solution is to put a relief somewhere in your pipes, close to the washing machine valve. This relief, called a permanent air chamber (or a water hammer arrestor), can be added to your pipes in the form of a sealed vertical copper tube filled with air. When the washing machine valve slams shut, the flowing water doesn’t have to slam against the closed valve; it now has another place to go.

The water fills the vertical pipe, and compresses the air in the otherwise empty tube. The air in the tube resists the flow of water and slows the water to a gentler stop, eliminating water hammer in the process. When the valve opens again, the water in the relief tube drains back into the supply pipe for your washer, and the tube is once again ready for the next sudden stop.

Over time, air in the permanent air chamber may be absorbed and the device will lose its effectiveness as a water hammer relief. Completely draining all of the pipes in your home by shutting off your main valve and opening all of your taps may allow the permanent air chamber to drain completely. Once the chamber is empty, the permanent air chamber will begin to relieve water hammer again.

As an alternative, a water hammer arrestor performs the same function but includes a rubber bladder that prevents air in the chamber from being absorbed into the water.

You may need help installing a relief in your plumbing to prevent water hammer. Boston Standard Plumbing can help you install a permanent air chamber or water hammer arrestor for your washing machine or dishwasher. Please call us at (617) 288-2911 to arrange a consultation.