Backflow / vent not shutting
I just started up my sprinkler and water is shooting out of my vent. I have a water shutoff on the outside and a shutoff to my sprinker. When I turn on the water it shoots out the bottom/vent. When I slowly open the sprinkler part it still shoots out the bottom. If I run a zone the water stops coming out the bottom and flows to the sprinklers but when it stops it shoots out the bottom again. Why is the vent/backflow not shutting? Can I fix this with out replacing the whole device?
Scott