Hi,
I live in a Houston TX suburb. We have very few freezing temperature
days in winter.

We have a sprinkler system put in place about three and half years
back by a contractor. I had to replace few heads due to wear and
tear, other than that no problems till now. Most of the parts used
are Watermaster(Orbit) and few big heads are Krain K8000 heads for
lawn. Timer controller is 57161 model from Watermaster which is good
for 6 stations. I have five stations with two for lawn and three for
flowerbeds. I have a Toro rain switch installed and attached to
Watermaster controller. We have a Watts back flow PVB valve
(http://www.wattsreg.com/default.htm?/es/800m4qt.htm) 800M4FR
installed before the zone controlling valve area. This spring when we
turned the sprinkler system on (timer) we noticed a problem. During
the sprinkling process the heads are going down every few minutes with
loud banging noise at the back flow valve and zone controlling valves
area. Both back flow valve and zone controlling valves are at the
same place. At the same time I noticed water leaking/gushing out of
back flow valve. I checked the timer to see if it is turning on and
off for some reason. It appears that timer is on as it is blinking
between showing time and zone information. I am not sure where to
look for troubleshooting. By reading news groups/use net I thought is
some way related to water hammer. But I am not sure how to check on
it.

Any help is appreciated.

Thank you,
Bharathi