Reduced pressure zone device

Lastly, an air gap or barometric loop are methods to prevent backflow from taking place.

[5] They are considered suitable because they prevent both back pressure and back-siphonage, because of a redundant design (even with two check valves broken the device still provides protection), and because they are testable to verify correct operation.

The device consists of two independent check valves, plumbed in series, with a pressure monitored chamber between (also known as the zone).

Four test cocks are installed to allow an inspector to verify proper operation of the valve with a differential pressure meter.

Some normal water use conditions may cause short episodes of discharge (this is why check one has a minimum passing value of relief +3.

An example of where backflow would harm the water supply is the use of well washing devices inside underground sewerage pumping stations.

In the UK,[6] Illinois, New York,[7] Texas,[8] and Missouri(RsMO 10c60-11), the RPZD valve must be tested at least every 12 months by an accredited tester.