Your valve’s diaphragm requires cleaning. If you are skilled in taking small components apart it’s not complicated. Shut off water to irrigation system and turn on a zone to release pressure. Open valve box and remove screws from the top of the problem valve (take photo of solenoid position on valve to make reassembly easier). Please note some water will fill into valve box once valve is taken apart, so plan for this. There is a spring on top of the diaphragm, so take care not to lose it. Lift off assembly and clean diaphragm and seat with non abrasive cleaner, check for rips in diaphragm, if ripped replace diaphragm and seat, see link below for image: Hunter 332100 Diaphragm Assembly Kit for PGV, SRV, ASV Valves - 1" Valves - EvergreenSprinklers.com
