Rotary valve actuator with high-low-high torque linkage

In a rotary valve actuator for controlling fluid flow through a rotary shaft control valve, including an actuator linear movable member, a rotatable lever coupled to said rotary shaft, and actuator linkage coupling the actuator linear movable member to said rotatable lever and defining a torque lever arm for converting linear movement of said movable member to rotary movement of said rotatable lever for rotating said rotatable lever in one rotatable direction from an initial actuating lever position corresponding to an initial high torque requiring position of said rotary shaft control valve, continuing rotation in said one rotatable direction to a mid-travel actuating lever position corresponding to a mid-travel low torque requiring position of said rotary shaft control valve, and continuing rotation in said one rotatable direction to an ending actuating lever position corresponding to an ending high torque requiring position of said rotary shaft control valve, the improvement comprising:

• said actuator linkage including a link member pivotally connected at one end to said actuator linear movable member and pivotally connected at the other end to said rotatable lever;
• said actuator linkage at said initial actuating lever position and at said ending actuating lever position providing said torque lever arm longer than the torque lever arm at said mid-travel actuating lever position to enable a high-low-high actuating torque capability of said rotary valve actuator during rotating of said rotatable lever in said one rotatable direction thereby matching said high-low-high torque requiring positions of said rotary shaft control valve.