"Eric R Snow" wrote in message
...
On 26 Apr 2006 20:48:00 GMT, Dave Hinz wrote:

On Wed, 26 Apr 2006 21:38:24 +0100, David Billington
wrote:
I can't remember the specific equations now that show when water hammer
will occur but water hammer is caused when the valve controlling flow is
shut down too rapidly causing a pressure pulse in the system. Is there
any way to slow the closure of the control valve.

It can also happen when opening a valve too rapidly. Think pulse-jet,
it's probably the same mechanism. But the fix is to, as someone else
said, puta vertical air-filled column to the pipe in question, to
absorb the impulses and smooth them out so they can damp down to zero.

You can buy fancy spring-loaded space age water hammer arrestors, or you
can make 'em out of 18" of 3/4" pipe and a cap. The latter works great
for my house.
When installing new shower valves and new washing machine valves in
my house I made up my own water hammer prevention devices. I just used
lengths of copper pipe and caps like everyone else does. I told a
plumber friend about this cheap fix compared to the ones at the store
and he said that the ones I made will eventually become waterlogged
and the only fix would be to drain them. In his years being a plumber
he had seen this many times. However, the ones I made stopped the
water hammer and lasted at least 6 years before I moved. And the ones
in my shop have been working for 7 or 8 years so I'm not sure it
always happens.
ERS

A solution to this problem is to put a tire valve on the top to allow air to
be pumped back in.

Steve.