The Principle Operation of a Pressure Vacuum Breaker Backflow Prevention Device Assembly – Installation Considerations

The PVB is not designed or approved to be installed where backpressure would be an issue, such as on a water service line to a building. The PVB is designed to withstand continuous pressure therefore, shut-off valves can be installed downstream of the PVB. Because of the design limitations, the PVB shall be installed at least 12 inches above the highest existing outlet measured from the opening of the check valve. The PVB can be tested in-line to evaluate the operation of the check valve to close drip tight and the air inlet to open to the atmosphere. The PVB can also be repaired in-line as well. (In-line means not having to physically remove the device from its present position). Unlike the RPZ, the PVB will not visually indicate check value failures. The PVB is designed for continuous pressure conditions however; continuous pressure for long periods could prevent the air inlet valve from opening because it could adhere to the air inlet valve seat due to high temperatures and water quality conditions. Continuous pressure has been defined to mean in use continuously for not more than twelve hours. Because of these issues, a certified tester should test the PVB at least annually. Testing of the PVB is required, since the only time it is know that the PVB is working properly is when it is tested. The SRPVB shall not be installed where toxic fumes may enter the air inlet valve during a backsiphonage event.