NORMAL WORKING UNDER PRESSURE

A BA backflow preventer protects the drinking water network by interrupting the continuity of the supply to the user, emptying and evacuating to waste in case of danger of water being turned back into the main pipeline.

IN FLOW
The two check valves are open ; the discharge valve is held closed by the dominant upstream pressure pushing the membrane from above. The downstream installation is served.

FLOW INTERRUPTED: STATIC PRESSURE

The two check valves are closed and the discharge valve is closed by the positive differential pressure pushing down on the membrane.
The downstream installation is no longer served.

IN CASE OF INCIDENT : HOW THE SAFETY MECHANISM WORKS

No reversal or indeed balance of pressure is permitted between the middle chamber of the backflow preventer and upstream. The design of the device ensures that upstream pressure must always be 140 mbar higher than pressure in the middle chamber. This differential pressure controls the opening of the discharge valve and emptying of the backflow preventer.

A controllable backflow preventer activated by reduced pressure protects itself against its own possible malfunctions.

The safety mechanism of the device comes into play when the pressure is static. In this case the discharge valve evacuates. This occurs in the following cases.