The law requires NYC backflow preventer testing after installation because backflow prevents serious risks. If a backflow prevention device fails, then pollution or other kind of contamination can compromise potable water. Preventers can vary in design, but most generally fall into one of three core classes: vacuum breakers, double-check valves and reduced-pressure valves.
There are two main types of vacuum breakers: atmospheric and pressure. An atmospheric vacuum breaker or AVB is among the simplest, most efficient and most cost-effective solutions, but it prevents only against backsiphonage and not back pressure. The pressure vacuum breaker or PVB is an advanced form of the AVB that can be tested due to the test cocks included. It also is only applicable to situations where backsiphonage is the concern.
The double-check valve or DCV features two independent check valves as well as stop valves, shut-off valves and test cocks. Innovated in the 19th century, this approach is still used today will little refinement to the original design. It’s among the most widely used preventers and suitable for protecting against both backsiphonage and back pressure.
A reduced-pressure principle backflow preventer or RP meet all AWWA standards and has been sanctioned by the Conference of State Sanitary Engineers. This was first introduced in the 1940s as a safer alternative to the double-check valve. Since these devices discharge to the atmosphere, they can often be used where regulations require an air gap, which isn’t possible with the double-check approach.
Air-gap separation, often abbreviated AG, is among the oldest methods of backflow prevention. It’s specifically used when there are cross connections, such as a T connection, where backsiphonage or back pressure may cause backflow. Although not included in the three core classes mentioned in the opener, it’s often the only method approved for this particular risk in certain scenarios.