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I opened up the wall to relocate my washer's water feeds and discovered an interesting double pipe arrangement. For each of the cold and hot feeds, there is an extra arm/appendix about 3feet long that dead-ends into an end cap. What's that for?

I'm guessing it's some sort of homemade water hammer arrestor? If so, why/how does it work (does it matter if it points up or down, or how far from the spout it is, etc.)?

double pipe

init_js
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1 Answers1

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Seems to be an arrestor.

They work by being pointed up so there is an air pocket at the top. the air pocket creates a cushion for the water when taps/faucets are turned off.

For the size you have, guess they had a couple of three foot lengths left over and did not want to cut the pipe again and had the room.

It might also have been added to add future plumbing to and seem like a good place.

crip659
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