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

Or when the valve is opened too quickly, presumably, anything that causes a
pressure spike ..



This may be offf use http://www.plastomatic.com/water-hammer.html

Good site, not very technical, he and I looked it over together.

GWE


Grant Erwin wrote:

I just ran into my old boss. He is now retired, and an avid gardener.
He put in a 12-zone automated watering system, and there is a problem
in it which is driving him bonkers. I'm posting this because you guys
know everything worth knowing.

His water system starts at the meter, then it runs to a tee, and off
of one leg goes his entire outside watering network. The other leg of
the tee goes to his house. Where the water enters his house, he has a
pressure reducing valve. On the outside watering leg, there is a
backflow prevention valve to ensure that even in the event of negative
city water pressure his gardening water can never wind up in his
neighbor's water glass.

At 4AM his watering system turns on. When the first zone valve cuts
on, the water pipes *in his house* begin hammering loudly. Eventually
it dies down and then the first zone valve cuts off and the second one
cuts on, no more problems. But the water hammering wakes him and his
family up every morning, and they worry about it damaging their house
piping because it sounds so violently loud.

They have had the water department guys out to check his pressure
reducing valve, his backflow prevention valve, and the water pressure
everywhere, and they say everything checks out OK. He has had two
different irrigation consultants come out and other than suggesting
things like reprogramming to try a different zone valve to come on
first (didn't help) they were similarly unable to come at the root
cause of the problem, nor could they suggest a workaround.

I don't really understand the phenomenon of water hammering, but I do
understand that it is a pressure oscillation which is characteristic
of an underdamped mechanical system. I suggested that he try adding
resistance (some kind of flow reducer, maybe a gate valve) or
capacitance (one of those bulb thingys) but he is on fire to find the
actual root cause and solve it, not just find a workaround. I
suggested he try shutting the gate valve, the main water shutoff valve
to his house, about 95% tonight to see if the added resistance might
do the trick.

Anyone got any bright ideas? This guy is no dummy; he was an
engineering manager and has a EE degree from Rensellaer Polytechnic ..

Grant Erwin
Kirkland, Washington