Hmm. Had no idea.
Seems to be a California thing:
Apparently a “flow through fire sprinkler system”.
Now THAT will be a surprise to the plumber who changes an angle stop, after having shut what-they-thought-was-the-main shutoff!
Aren’t shut off valves located at the water meter like typically around here? …which, your flow through design picture indicates would shut off the sprinkler water with the domestic water.
The domestic and sprinkler shutoffs are separate. Those systems branch.
So if you have a clean water flow through sprinkler, then shutting the main won’t turn off water to the toilets.
So, you don’t have main shutoffs at the water meter like most states, as indicted in the below picture?
Got another name for it “passive purge systems”. It avoids the need for backflow prevention to protect the public water system from stale sprinkler pipe water.
And, avoids the pressure drop of a backflow device.
