Minnesota adopted a new plumbing code in January of this year and, of course, that brought many new plumbing code requirements. I blogged about the new Minnesota plumbing code earlier this year, but there was one change I never mentioned: a new requirement for water hammer arresters. The old Minnesota plumbing code required "protective devices or approved mechanical shock absorbers" to be installed when noises were created due to water hammer (4715.1750). But the new plumbing code doesn't give any wiggle room, specifying exactly how this must be done.

The new plumbing code says the following:

In other words, water hammer arresters are now required -- they are no longer a mere suggestion. You'll most commonly find "quick-acting valves" on dishwashers and clothes washing machines. Also, the standard referenced in Table 1401.1 is ASSE 1010-2004, Water Hammer Arresters.

More on water hammer

Water hammer occurs when a bunch of flowing water is suddenly stopped, causing a shockwave as shown in the diagram below:

While water hammer is worst with the aforementioned quick-acting valves, it can really happen anywhere. I had a small problem in my own kitchen sink after replacing my 1/2" water line with a 3/8" water line to get hot water to my sink faster. All it took to fix the issue was to secure the water line, but the "before" video was quite dramatic. All that I'm doing in the video below to get the pipe to bang is turning my hot water on and off at the kitchen faucet.

The most common water hammer arresters that I find in homes are made by Sioux Chief. There is some excellent information about water hammer arresters on the Sioux Chief website, along with some good video clips showing how water hammer arresters operate:

These products are available at home improvement stores and plumbing supply stores. The most common place for water hammer is at washing machine hoses. If you experience water hammer at your own washing machine connections, the quick and easy solution is to purchase a set of water hammer arresters made specifically for washing machines. These have a standard 3/4" hose thread and are about as much work to install as connecting a garden hose to a faucet.

Author: Reuben Saltzman, Structure Tech Home Inspections