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?
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
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
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
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?
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.
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