System for precise position control

A system for precise control of flow through a rotary pipeline valve comprising:

• a rotary valve positioned in a pipeline;
• a double acting hydraulic cylinder including a piston adapted to drive said rotary valve in opposite directions through a quarter turn between full open and closed positions;
• a source of pressure fluid;
• a low pressure exhaust zone;
• pressure conduit means connected from said pressure source;
• exhaust conduit means connected to said exhaust zone;
• first and second duct means, connected to said cylinder on first and second sides of said piston respectively;
• signal actuated direction control switch valve means in each of said first and second duct means, operable in a first position to enable flow from said pressure conduit means and to block flow to said exhaust conduit means and in a second position to block flow from said pressure conduit means and enable flow to said exhaust conduit means;
• said cylinder being conditioned to turn said valve toward closed position when said first duct means is connected to said pressure conduit means and said second duct means is connected to said exhaust conduit means;
• both of said direction control switch valve means being normally in said first position;
• a one-way valve on the inlet side of each of said switch valve means preventing reverse flow through said pressure conduit means;
• signal actuated rate control means including three flow lines connected in parallel in said exhaust conduit means, and an on-off binary valve in each of said flow lines, the flow capacity of each of said binary valves being a multiple of the flow capacity of the next smaller binary valve;
• said direction control switch valve means and said rate control binary valves being electrical signal-actuated from a normal position;
• means biasing one of said binary valves into a normally open position and means biasing the other binary valves into a normally closed position;
• a pressure transmitter connected to said pipeline and operative to transmit signals to said controller representative of a pipeline flow characteristic;
• and
• a controller operable to transmit electrical signals, when signals from said transmitter indicate a deviation of said flow characteristic from a selected value, a direction signal to that one of said direction control switch valve means for correction of flow characteristic and, when the needed rate of correction exceeds the capacity of said one binary valve, a rate signal to selected ones of said other binary valves.