I have never been around a backflow device in underground sprinklers before and now its my job to winterize same. Thats the easy part.
The hard part is its down in a terrible crawl space on other end of house from access hole. Question is can you blow air into the supply line AFTER the backflow device? Thinking it should hold the air pressure in just like keeping water from backing up.
I have access to the supply line without crawling. It is after the bf and before the zone valves
The next issue is valve is leaking anyway,,,thinking of adding an electric valve that turns the whole system on and off. And would need another valve on the electric shutoff on drain side so no crawling required fall and spring
How do you put electric solenoids in and control them from other end access,,,how do you control them???
thinking more---if I am relying on elec valves to supply and stay closed to keep crawl space dry,,,what happens in a power failure when valves lose juice and city water is still on?? Does the crawl space fill with water?
You need to blow out the back flow as well. Is there an shutoff or accessible section of pipe before the back flow? You could install a connection point to blow out the system. If the back flow is leaking, it might not protect your internal water supply. Depends upon the leak.
Valves use low voltage power to open them. If you had a power outage, the valves would be closed. Some irrigation controllers have a master pump relay. You could use it to open your main valve.