The Principle Operation of a Backflow Prevention Device for Beverage Dispensing Equipment – Normal Operation and Pressure Loss
When BPBDE is in a static state and pressurized, the first seats against the atmospheric diaphragm closing the atmospheric vent. Second check valves seals against the seat and closes tight.
When a flow is initiated downstream, the first check valve opens away from the atmospheric vent diaphragm. Supply pressure keeps the atmospheric vent closed. The second check valve opens to allow water to flow through the BPBDE.
A dual check valve alone without an atmospheric vent will not show any signs of failure. If there is a failure of the second check valve and backpressure conditions exists there would be no indication of the failure. With a dual check valve with an atmospheric vent, if the second check valve failed to close during a backpressure condition, the atmospheric vent will open and discharge water and/or carbon dioxide gas. This discharge is a visual indication that the second check valve has failed.
As water flows through the BPBDE there is a pressure loss that is created by the force loaded check valves and the atmospheric diaphragm. At 0 gpm, the pressure loss is about 5 psi depending on size and manufacture. At a flowrate of 1 gpm, the pressure loss is depending on size and manufacture, approximately 8 psi to 10 psi.