That is where a one way check valve will help you.
using anti-siphon valves
- Thread starter mzimmers
- Start date
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Here’s an example from our water provider on how they install backflow protection for an irrigation meter. 
mzimmers
Active Member
Not to beat this to death, but...if the valve should be above the sprinkler heads, then why is it considered a good idea to bury them in plastic boxes?
Sprinkler heads and most of the pvc is buried underground, therefore the valves buried in a box essentially are at curb level.
