[Shop-talk] [Bulk] Re: Seasonal water hammer?

[David Scheidt]

> On Nov 5, 2014, at 14:52, "Karl Vacek" <KVacek at Ameritech.net> wrote:
>
> I'm not a plumber though I do all my own work.
>
> Ideally, every water outlet should have a hammer trap - one for cold, one
> for hot.  Most simply, a hammer trap is teed into the supply line as close
> as possible to the outlet.  A trap includes at least a foot of pipe of the
> same size as the run (or even better a size or two larger), oriented
> vertically up from the tee, with a cap at the top.
>
> If you don't have hammer traps you will likely get water hammer.  Hammer
> traps do tend to fill up with water as the air entrapped in them gradually
> becomes absorbed into the water.

If you have hammer traps, and you don't have water hammer, you
wouldn't have water hammer if you didn't have them.

Air chamber hammer traps simply don't work. They're full of water, and
not air, in a few days to a few weeks, depending on the usage, the
water pressure, and pipe sizes.  Once they're full of water, their
only purpose is to grow bacteria.  Even when they're newly drained,
they're invariably too small.

Water hammer is prevented by using proper pipe design to keep flow
rates below about 5 feet per second, and by keeping branches as short
as possible.  If you meed an arrestor, use a mechanical one sized for
the job.