zone back two independent check valves all cross-connections subject to main ... supply lines with intermediate relief valve backpressure or back siphonage ... hazzard cross connections supplied with shut-offvalves where there is a high potential ... pressure detector assy high hazzard rpz valve backflow preventers with a water meter ... in by pass line fire protection system supply main detects leaks and unauthorized use ... -connections subject to double check valve assembly two independent check valves ... testing continuous pressure tions main supply lines food cookers tanks vats lawn ... pools fire sprinkler lines res supply lines at the meter residential fire ... in by pass low hazzard line dual check valve backflow preventer for low hazard cross ... app laboratory faucet dual check valve with intermediate vacuum breaker in ...