The Principle Operation of a Pressure Vacuum Breaker Backflow Prevention Device Assembly Check Valve and Air Inlet Valve Springs
The check valve is force loaded closed and the air inlet valve is forced loaded open. The air inlet valve is held closed by supply pressure and the air inlet spring is trying to keep it open. The air inlet valve is located downstream of the check valve and will open with the assistance of the air inlet spring when the pressure in the body of the PVB upstream of the air inlet valve is atmospheric. The air inlet valve when open will introduce atmospheric pressure to breaks the vacuum during a backsiphonage event. The spring loading of the check valve provides the ability to bite through small debris and still seal preventing a reversal of flow, a protection feature not prevalent in unloaded check valves. The check valve spring shall be force loaded to not less than 1.0 psi. The air inlet valve shall be force loaded to no less than 1.0 psi. Since the air inlet valve is force loaded to no less than 1.0 psi, it will open when the water pressure downstream of the check valve is equal to the tensile strength or loading of the air inlet spring. The maximum allowable pressure loss through the PVB is 10 psi.