What is backflow preventerin construction?

An RPZ (reduced pressure zone) assembly has two check valves with a monitored pressure zone between them and a relief valve that discharges water if either check leaks, so it protects against high hazard cross connections, the ones that could make people sick. A double check valve assembly has the two checks but no relief port, so it is limited to low hazard connections. Because an RPZ can dump water when it operates, it must drain to an air-gapped receptor, which a double check does not need.

In most US jurisdictions, yes. Cross-connection control programs run by the water purveyor typically require testing at installation, after any repair, and annually thereafter, performed by a certified backflow tester who files results with the purveyor. It is a recurring owner cost that scales with the device count, so a campus with dozens of assemblies carries a meaningful annual testing line. Include initial certification in the bid and flag the annual obligation to the owner.

It splits by service. The plumbing contractor typically furnishes and installs the assemblies on the domestic and irrigation lines, while the fire protection subcontractor handles the detector assembly on the fire service. A site utility contractor may set an exterior assembly in a vault or enclosure. At bid time, check each sub's scope letter, because the fire line device is a classic gap where two subs each assume the other carried it.