Rack and pinion actuator is the most commonly used pneumatic actuator. The middle of the cylinder is connected with the rack and pinion. Rack and pinion type can be divided into double acting type and single acting type. At present, the inner diameter of the rack and pinion actuator cylinder can be 400 mm, the double acting output torque is 8 knm (the air pressure is calculated as 0.55 MPa, the same below), and the single acting output torque is 5 knm.
The structure of double acting rack and pinion pneumatic actuator is shown in Figure 1. When the air source pressure enters the middle cavity between the two pistons of the cylinder from the air port a, the piston 2 moves towards the end 2 of the cylinder, and the air in the air cavity at the end 2 is discharged through the air port B. at the same time, the rack of the piston 2 drives the output shaft (gear) to rotate synchronously. On the contrary, when the air source pressure enters the air chamber at the end 2 of the cylinder from the air hole B, the piston 2 moves towards the middle of the cylinder, and the air in the middle air chamber is discharged through the air port A. at the same time, the rack of the piston 2 synchronously drives the output shaft (gear) to rotate in the opposite direction to realize the opening and closing of the ball valve. The output torque of double acting cylinder is linear (Fig. 2).
The structure of single acting rack and pinion pneumatic actuator is shown in Figure 3. When the air supply pressure enters the middle cavity between the pistons of cylinder 2 from the air port a, the piston 2 moves towards the end of cylinder 2, forcing the spring at the end of cylinder 2 to compress, at the same time, the rack of piston 2 drives the output shaft (gear) to rotate synchronously. When the air source pressure is shifted backward through the solenoid valve, the air in the middle air chamber is discharged from the air port a, and the 2 piston of the cylinder moves to the middle direction under the action of the spring force, so that the 2 piston rack synchronously drives the output shaft (gear) to rotate in the opposite direction, so as to realize the opening and closing of the ball valve. The output torque of single acting cylinder is linear (Fig. 4).
(b) spring return working stroke table