Low flow rate meter

Claim 1

A FLOW METER FOR MEASURING THE FLOW OF GAS INTO A LOW PRESSURE REGION COMPRISING, MEANS FOR LEAKING A FLOW OF GAS INTO SAID LOW PRESSURE REGION, A GAS INLET CHAMBER OF VERY SMALL VOLUME HAVING GAS IMPERVIOUS WALLS AND A QUANTITY OF GAS CONTAINED THEREIN AT AN INITIAL PRESSURE CONNECTED TO SAID LEAK MEANS, MANS FOR SENSING CHANGES IN PRESSURE WITHIN SAID GAS INLET CHAMBER, SAID MEANS COMPRISING A DIFFERENTIAL PRESSURE METER INCLUDING A FIRST SMALL VOLUME, A SECOND CHAMBER AND A THIN GAS IMPERVIOUS FLEXIBLE MEMBRANE SENSITIVE TO SLIGHT CHANGES IN PRESSURE SEPARATING SAID FIRST AND SECOND CHAMBERS, SAID FIRST CHAMBER FORMING A PORTION OF SAID GAS INLET CHAMBER, SAID MEMBRANE FORMING A PORTION OF SAID GAS IMPERVIOUS WALLS, MEANS FOR ESTABLISHING AND MAINTAINING WITHIN SAID SECOND CHAMBER A PRESSURE IDENTICAL TO THE INITIAL PRESSURE WITHIN SAID GAS INLET CHAMBER, FIRST MEANS SUBJECTED TO THE PRESSURE WITHIN SAID GAS INLET CHAMBER FOR VARYING THE VOLUME OF SAID GAS INLET CHAMBER SO AS TO MAINTAIN CONSTANT PRESSURE WITHIN SAID GAS INLET CHAMBER, AND MEANS COOPERATING WITH SAID VOLUME VARYING MEANS FOR MEASURING THE CHANGES OF VOLUME OF SAID GAS INLET CHAMBER.