I just flushed out a zone for the second time in two weeks. The first time I was checking it the client turned on the zone and all the sprinklers were clogged so I told him to shut it off and removed the nozzle on the 570z. I thought the system was off since nothing came out, I was looking straight down the sprinkler when all of a sudden I got a face full of sand. I mean sand in my eyes, hair, ears, and even up my nose. After I hosed some of the sand off I went through and flushed every head out, the nozzles weren't clogged just the screens. Today I was called out again for the same problem on the same zone. Can anyone tell me how this one zone is getting full of sand? This zone has about 6 Toro 570z's and a 1" Hardie inline valve. The property doesn't have a well and none of the other zones are affected. Also there is plenty of pressure on this zone. Any ideas?