It's important to understand what water hammer is.

When a column of water is moving through a pipe and then the water is stopped very quickly, the inertia of the water has considerable force behind it. Since water can't compress, there's nothing to cushion the impact other than flexing the walls of the pipes, etc.

Water hammer arresters work by providing an air cushion, near the "point of impact" such as the valve that is suddenly closing. An expansion tank elsewhere in the system won't do much good. The item that you are looking at should help considerably.

I would start with one on each of the washing machine lines. They do sell something similar for the dishwasher.

Something to look for is if the air chamber is sealed from the water. If not, the air cushion eventually dissipates. Since the product you are looking at will work upside-down, it suggests a sealed chamber.

BTW: The LG washing machines are cool. Part of what it is doing is determining how much water to add. It is adding water a little at a time and then checking the resistance to turning the tub.

Thanks for the detailed info. I picked up two of these to put on my washer, as a start. I may have seen the one that would work for the dishwasher, but it was meant to be sweat onto the line. Thanks for helping clear up the difference effectiveness between these and the expansion tank.

As for the LG's, yes, they do that fill - pause - fill routine, but the part that jolts the water lines is the very start of the cycle. (The first 10 ~ 15 seconds.) Other than that, I love them! A little overkill, but there's nothing they can't clean!

Contrary to the common opinion, water velocity has very little to do with water hammer.

Water hammer occurs because while the flow is occurring the internal pressure in the line drops to Dynamic head pressure, which is static head pressure minus Friction head loss and vertical static head loss. The moment that the flow stops the entire piping system immediately jumps back up to static head pressure which results in water hammer. This explains why water hammer often occurs on long lines at a fairly good distance away from the offending valve.

I installed the units you linked to.. they work GREAT.

It's always good to hear positive feedback on something you buy. Whew!

My pipes bang in the opposite corner of the kitchen from where my faucet is installed - typically while running the water. I get a consistent low level hammer. Where should the arrester be installed? At the faucet, or at the nearest valve where the banging is occurring?

Here is a link that might be useful: Diy crib

Ideally, it is best to have an anti-hammer device at every faucet/valve. If you have hammering, it is likely the result of a lousy plumber. Many like to skip the expansion tube at each location because it saves them $2 per location. Some install 1 larger expansion tube at the highest level, but it does not work as well as every location having its own.

The products offered at the big box stores should work fine, as a fix for shoddy plumbing practices. BTW, the absence of expansion tubes is not a code violation in most jurisdictions (even though it should be) and technically will not cause problems other than the noise.

Talk about threads that refuse to die. This issue was raised, solved and buried in 2007,resurrected 4 years later,buried and forgotten again for 4 years and true to form it's back.

Oh well,were it not for plumbing noise at my house I couldn't tell when kids skiped their showers and went straight to bed. (;

If you have hammering, it is likely the result of a lousy plumber. Many like to skip the expansion tube at each location because it saves them $2 per location.

Get a clue.

They are called water hammer arrestors and they are about $15 each. So all fixtures except toilets would be an extra $30. Plumbers would add the cost to their quote and the homeowner would choose the cheaper guy. If you request water hammer arrestors to be installed, the plumber will happily do it if you will pay for the upgrade. It has nothing to do with plumber laziness.