Anti-Hammer Water Arrester Question

braytonakSeptember 26, 2007

My water line does not have an expansion tank on it. My LG washer loves to diddle around with the water when it first starts. (My guess is that it's sampling the water temperature, or it's trying to fill the soap cups without foaming over.) It turns off and on repeatedly at least six or seven times...per line. My dishwasher is even worse. It sounds like I'm banging my hand on the wall when it turns off.

I found this item on the Lowe's web site (it may ask you for your Zip code...put in 99517 to see what I see):

Is this kind of item pointless because of its small size? Due to the amount of stress this causes on my pipes, I was even thinking of putting one on each end of the washing machine hoses. Although an expansion tank is the best thing, I won't be able to get that installed until next year. (Sometimes when you just don't have much money left, you just don't have much money left!) One thing that's annoying is seeing that this item is $6 cheaper in the Seattle area. Hmpf.

Are these ever sold to go on dishwasher lines, too?

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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.

    Bookmark   September 27, 2007 at 9:18AM
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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!

    Bookmark   September 27, 2007 at 11:52PM
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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.

    Bookmark   September 28, 2007 at 1:50AM
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I installed the units you linked to.. they work GREAT.

    Bookmark   September 28, 2007 at 8:32AM
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It's always good to hear positive feedback on something you buy. Whew!

    Bookmark   September 28, 2007 at 10:47PM
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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

    Bookmark   June 2, 2011 at 5:08PM
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