I remember hearing once that if the valve closed faster than the time it
would take a sound-pressure wave to travel the length of the pipe, they
would hammer. I don't know how much length of the pipe you'd consider since
really, its flowing all the way from the source.


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. I would guess the
details shouldn't be difficult to find and the equations were fairly
simple IIRC.