Fluid control valves

Claim 1

A CONTROL VALVE FOR USE IN A FLUID CONDUIT COMPRISING: A TUBULAR BODY HAVING AN INTERMEDIATE VENTURI THROAT FORMING A VALVE SEAT, A VALVE STEM SUPPORTED AXIALLY OF THE TUBULAR BODY FOR SLIDABLE MOVEMENT AND EXTENDING THROUGH SAID THROAT, A PLUG CARRIED BY SAID STEM ON THE UPSTREAM SIDE OF SAID THROAT, A PISTON CARRIED BY SAID STEM ON THE DOWNSTREAM SIDE OF SAID THROAT, A CYLINDER FOR SAID PISTON PROVIDING FLUID PRESSURE CHAMBERS ON BOTH THE UPSTREAM AND DOWNSTREAM SIDES OF THE PISTON, MEANS SUPPORTING SAID CYLINDER IN THE BODY WHILE PERMITTING SUBSTANTIALLY STRAIGHT FLOW THROUGH THE BODY AROUND THE CYLINDER, PRESSURE SENSING MEANS BY TRANSMITTING UPSTREAM PRESSURE TO SAID FLUID PRESSURE CHAMBER OF THE CYLINDER ON THE DOWNSTREAM SIDE OF THE PISTON TO URGE THE PLUG AWAY FROM THE THROAT, MEANS AFFORDING COMMUNICATION BETWEEN A PORTION OF THE VALVE BODY DOWNSTREAM OF SAID PLUG AND SAID FLUID CHAMBER OF THE CYLINDER OF THE UPSTREAM SIDE OF THE PISTON FOR TRANSMITTING PRESSURE TO URGE THE PLUG TOWARD THE THROAT, A FLUID DISCHARGE LINE IN COMMUNICATION WITH SAID CYLINDER ON THE DOWNSTREAM SIDE OF SAID PISTON, A PILOT VALVE IN SAID DISCHARGE LINE HAVING A VALVE MEMBER CONTROLLING THE BLEEDING OF FLUID FROM SAID CYLINDER THROUGH SAID DISCHARGE LINE AND HAVING PRESSURE RESPONDIVE MEANS FOR MOVING SAID VALVE MEMBER, AND PRESSURE SENSING MEANS COMMUNICATING AT ONE END WITH SAID PRESSURE RESPONSIVE MEANS OF THE PILOT VALVE AND HAVING SPACED BRANCHES AT ITS OPPOSITE END, ONE OF WHICH CONNECTS WITH A RESTRICTE PORTION OF THE VENTURI THROAT DOWNSTREAM OF THE PLUG AND ADJACNET THERETO AND THE OTHER OF WHICH CONNECTS FARTHER DOWNSTREAM IN THE VALVE BODY BETWEEN THE PLUG AND SAID CYLINDER, AND A NEEDLE VALVE IN SAID LAST MENTIONED BRANCH, SAID NEEDLE VALVE BEING SO ADJUSTABLE AND THE POINTS OF CONNECTION OF SAID BRANCHES WITH THE VALVE BODY BEING SO LOCATED WITH RESPECT TO THE VENTURI THROAT AND WITH RESPECT TO EACH OTHER THAT THE DIFFERENCE IN PRESSURE AT THE TWO POINTS OF CONNECTION IS EQUAL TO THE FRICTION LOSS DOWNSTREAM OF THE VALVE, WHEREBY THE SENSED PRESSURE ACTING UPON THE PILOT VALVE IS SUBSTANTIALLY THE SAME AS THE PRESSURE WHICH IT IS DESIRED TO MAINTAIN THE FLUID CONDUIT A PREDETERMINED REMOTE DISTANCE DOWNSTREAM OF THE VALVE UNIT REGARDLESS OF THE AMOUNT OF FLOW.