I recently replaced some old metal pipe that ran from the water supply to two sprinkler valves for my lawn with PVC. I also replaced the valves with two new ones and wired them to the existing automatic timer/controller. Everything worked fine for a couple of days, then one of the valves stopped turning on. I was in the middle of a project and didn't have time to investigate, so I just ran that one manually for a few days. Then they all (6) stopped working. I measured the voltage coming from the transformer that powers the system and found that there was none, where there should have been 24 V. I replaced the transformer with a new one. Again everything worked fine for a couple of days and then the new transformer went dead. Can anyone tell me what they believe is causing these transformers to fry?