The Principle Operation of a Pressure Vacuum Breaker Backflow Prevention Device Assembly – Flowing or Dynamic State
As water flows through a PVB with a demand downstream and the upstream and downstream shut-off valves open, the water pressure will force the spring-loaded check valve to open. Since the check valve spring is forcing the check valve to close, the water pressure will have to overcome the force of the check valve spring. This action decreases the water pressure to the amount equal to the tensile strength of the check valve spring. According to industry standards, the check valve spring shall have a minimum force loading of 1.0 psi. Once the check valve is open, the water pressure closes the spring loaded air inlet valve. The air inlet spring is forcing the air inlet valve to open. According to industry standards, the air inlet valve spring shall have a minimum force loading of 1.0 psi. The check valve will close as the inlet rate of flow decreased to a static state. If the check valve is operating properly, it will stay closed when the inlet pressure drops to sub-atmospheric preventing water downstream of the check valve from entering the potable water system. The air inlet valve will stay closed in this situation.