installing laundry outlet--water hammer plumbing

I'm installing a laundry box outlet with hot/cold copper supply lines. I plan to put inverted "T"s close to the outlets with a capped end on a short piece of vertical pipe. Probably will be using 1/2" copper pipe. My question is how long should these capped vertical pipes be? Is 12" about right?
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Capped pipes are worthless. They'll be filled with water within 3 months. Plumb in the box and just screw on Sioux Chief pneumatic water hammer arresters. They're only about $12
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Well they've worked for decades in the houses i've been in. Just where the hell do you think that air is going to go in 3 months???
s

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Sorry dude, they don't work--never did. Plus, they're not code. That's why you won't find the air chambers on any newer homes. They all have the pneumatic type. The air gets absorbed into the water. Plus, the air chamber can be a breeding ground for disease. Do an internet search on water hammer.
Here's the code:
604.Water harnmer. Thc flow velocity of thc water distribution system shall be controlled to reduce the possibility of'water hammer. A water-hammer arrestor shall be inslalled where quick-closing valves are utilized. Water-hamer arrestors shall be installed in accordance with the manufacturer's specifications. Water-hammer arrestors shall conform to ASSE 1010.
Notice it doesn't say "air chamber"
Here's a really good article from http://www.builderswebsource.com
Traditional Solution to Water Hammer
Traditionally, the solution to water hammer has been to install pipe risers inside the wall at each faucet or valve junction. Sometimes these risers would be as high as 24" or more, depending on the pipe diameter. In theory, the risers would trap air as the plumbing system is first activated. The column of air acts as a natural damper, compressing as it absorbs residual shock waves from a sudden change in the supply flow.
Many, if not most older homes today have such systems and some plumbers continue to install air risers because "that's the way they've always done it." However, what is not readily understood is that these risers eventually fail due to water logging. Over time, the trapped air in the risers dissolves into the water supply itself and the water level gradually rises until the air chamber is completely void of air at all. For this reason, some people who have never experienced the sound of water hammer may suddenly start complaining of "strange noises inside the walls."
The only real solution is to completely drain the home's water supply system at the lowest point and gradually re-pressurize it. However, this solution is temporary at best, since the air chambers will eventually become waterlogged once again, thereby eliminating their effectiveness.
What's more, further studies have also found possible health problems associated with air risers, such as an accumulation of rancid water, bacteria, minerals, and other muck that festers in the dark, dead-end chambers. If left unchecked and untreated, this could eventually contaminate the entire household water supply causing unexplained illness.
Therefore, modern practice and, indeed, many plumbing codes, now prohibit air chambers in new construction. In any case, if you are remodeling or building a new home, DO NOT use air chambers to mitigate water hammer problems. Rather, design the system right from the start and you'll never have to worry about it again. A combination of proper pipe sizing and water hammer arresters are all that's necessary in most situations.
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bullshit. mine still work after 25 years and the systems Never been turned off or drained.
you must own stock in the arrestor scam products. probably got a K$N filter on your truck also. LMAO!!
s

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How do you know they're still filled with air?
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On Sat, 18 Oct 2008 21:28:55 -0500, Rick-Meister
<snip>

For a 1/2" copper pipe how long should the capped vertical pipe be? Is 24" about right?
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wrote:

You're wasting your time. As noted in other posts, it's only a matter of time before the air becomes entrained ( absorbed) into the water and then it's all gone. Why do you think accumulators (or expansion tanks) have a diaphragm separating the water from the air? MLD
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Phisherman-
In spite of Steve's insistence that "air chambers" (capped vertical pipes) work....they can "appear" to work if the plumbing system & system pressure might present conditions where water hammer is naturally minimized.....they don't really work.
Rick-Meister's posts on the subjects have been "spot on".
Air chambers might work but only "temporarily".......the air in the capped pipe will be dissolve into the water in short order (months) , rendering the air chamber useless.
Design & installation of water hammer arrestors are based on established hydraulic engineering principles. Water hammer arrestors are needed to safely & quietly dissipate the kinetic energy contained in flowing water when fast acting valves are present.
Thinking water hammer arrestors are "a scam" makes as much sense as calling automobile shock absorbers a scam.
I recently "cheaped out" ......by not installing a water hammer arrestor on an upstairs toilet plumbed with PEX. I had assumed the natural compliance of PEX (when compared to copper) would provide water hammer prevention. No such luck, I still had water hammer. Adding a water hammer arrestor eliminated the problem.
cheers Bob
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