Method of controlling the exhaust of gases from a metal refining bath

Claim 1

IN A METHOD OF COLLECTING A GAS FROM AN OPEN CONTAINER SUBSTANTIALLY WITHOUT DILUTION BY THE AMBIENT ATMOSPHERE, THE STEPS OF: (A) DISCHARGING A STREAM OF SAID GAS FROM SAID CONTAINER IN A PREDETERMINED DIRECTION; (B) RECEIVING THE DISCHARGED STREAM IN THE ORIFICE OF A HOOD, SAID ORIFICE BEING SPACED FROM SAID CONTAINER IN SAID DIRECTION; (C) PASSING THE RECEIVED STREAM THROUGH SAID HOOD FROM SAID ORIFICE THROUGH AN OUTLET OF SAID HOOD TO AN EXHAUST CONDUIT CONNECTED TO SAID OUTLET; (D) MEASURING THE DIFFERENCE BETWEEN THE PRESSURE OF SAID AMBIENT ATMOSPHERE AND THE PRESSURE OF SAID GAS AT A POINT BETWEEN SAID ORIFICE AND SAID OUTLET IN SAID HOOD, SAID POINT BEING SPACED FROM SAID ORIFICE; (E) MEASURING THE VOLUMETRIC RATE OF FLOW OF SAID GAS PASSING THROUGH SAID HOOD; (F) PRODUCING A CONTROL SIGNAL IN RESPONSE TO THE MEASURED PRESSURE DIFFERENCE AND TO THE MEASURED RATE OF FLOW; AND (G) APPLYING SUCTION TO SAID STREAM OF GAS IN SAID EXHAUST CONDUIT IN RESPONSE TO SAID CONTROL SIGNAL IN SUCH A MANNER THAT THE DIFFERENCE IN THE PRESSURES OF SAID STREAM OF GAS AT SAID ORIFICE AND OF SAID ATMOSPHERE REMAINS SUBSTANTIALLY ZERO.