A reduced pressure assembly is the highest level of backflow protection available, and it is the one required wherever the consequence of a failure is somebody getting sick rather than somebody being annoyed.
It is two independent check valves like a double check assembly, with one thing added between them: a relief valve, and a chamber held at a pressure lower than the supply. That is the "reduced pressure" in the name, and it is the entire design.
Because the middle chamber is always at lower pressure than the supply line, water cannot move backward through it — pressure will not flow uphill. And if the first check starts to leak, the relief valve opens and dumps that water on the ground rather than letting it reach the chamber.
The part that surprises people
An RP that is failing discharges water. That is not a malfunction; it is the assembly doing exactly what it was built to do, choosing to waste water rather than risk the supply.
It also means an RP cannot be installed in a pit or a vault where a discharge has nowhere to go, and it needs an air gap drain sized for a full relief discharge. On a large assembly that is a real volume of water, and it is the reason the location of an RP is decided carefully rather than conveniently.
Where you find one
Anywhere the hazard is classified as a health hazard, anywhere backpressure is possible, and nearly always where both are true: chemical injection and fertigation, cooling towers, treated boiler loops, medical, dental and laboratory connections, industrial process water, commercial kitchens and livestock and agricultural supply.
Testing and freezing
Testable, certified once a year by a certified technician, report filed directly to your provider. An RP has more to verify than any other assembly — both checks, the relief valve opening point, and the margin between them — and it is the assembly most likely to need a rebuild rather than pass clean, because there is simply more rubber in it.
It also has to sit above ground with a drain under it, which puts it directly in the weather. A freeze splits the body, and the replacement costs several times what a blowout does.
Where one sits inside the building, we test and repair it but do not replace it — that line is explained here.
Schedule a backflow test or call 970-835-9661