The system is on an Orbit Control Panel, there are 12 zones 4 valves.From the best I can figure from past control valve failure, there are 3 zones on one valve, I can not figure that one out, but it was so. The system was put in 10 years ago. I cannot locate anything other than the 4 control valves, I took the suspect valve down and located that zone 4 also shares the control valve for 10 and 12. I located a break on zone 12 at a head and also noted that there was muddy water in a head on zone 4 can the back wash in zone 12 have clogged zone 4 as only one head has muddy water, all the others are dry.