Backflow prevention device with improved pressure sensing means

Claim 1

A BACKFLOW PREVENTION UNIT ADAPTED TO BE CONNECTED BETWEEN A WATER SUPPLY MAIN AND A SERVICE PIPE, COMPRISING: A FIRST CHECK VALVE AND A SECOND CHECK VALVE, SAID CHECK VALVES BEING ARRANGED IN SERIES, SAID FIRST CHECK VALVE HAVING AN INLET TO BE SUBJECTED TO THE PRESSURE IN SAID SUPPLY MAIN AND ALSO HAVING A SENSING PORT IN COMMUNICATION WITH SAID INLET, AND SAID SECOND CHECK VALVE HAVING AN OUTLET TO BE SUBJECTED TO THE PRESSUREEIN SAID SERVICE PIPE; A FLOW CONTROL ELEMENT IN SAID FIRST CHECK VALVE ARRANGED TO PREVENT REVERSE FLOW THROUGH THE INLET OF SAID FIRST CHECK VALVE; A RELIEF VALVE HAVING PRESSURE DIFFERENTIAL RESPONSIVE MEANS CONTROLLING FLOW THERETHROUGH, SAID RELIEF VALVE HAVING AN INLET COMMUNICATING WITH A ZONE BETWEEN THE OUTLET OF THE FIRST CHECK VALVE AND THE INLET OF THE SECOND CHECK VALVE FOR EFFECTING DRAINING OF SAID ZONE WHEN A PREDETERMINED PRESSURE DIFFERENTIAL IS EFFECTIVE UPON SAID PRESSURE RESPONSIVE MEANS OF SAID RELIEF VALVE; MEANS CONNECTING SAID PRESSURE RESPONSIVE MEANS OF SAID RELIEF VALVE WITH SAID SENSING PORT AND WITH SAID ZONE, RESPECTIVELY, FOR APPLYING THE PRESSURE AT SAID SENSING PORT AND SAID ZONE TO SAID MEANS; AND MEANS IN THE INLET OF SAID FIRST CHECK VALVE FOR DIVERTING AND ENTRAPPING A PORTION OF THE INCOMING WATER TO ASSURE RAPID TRANSMISSION OF THE PRESSURE OF SAID INCOMING WATER OF SAID PRESSURE RESPONSIVE MEANS.