AT series pneumatic actuator takes SR series pneumatic actuator as an example in the application of spring reset. The output torque is obtained in two different operation processes. According to the travel position, two different moment values are generated in each operation. The output moment of spring reset actuator is obtained by multiplying the force (air pressure or spring force) by the arm. The first condition is that the output moment is obtained when air pressure enters the compressed spring in the middle chamber, which is called "air stroke output moment". In this case, the air pressure forces the piston to change from 0 degree to 90 degree because of the spring pressure. Shrinkage produces reaction force and the maximum moment decreases gradually from the starting point to the second condition: the output moment is the spring restoring force acting on the piston when the middle chamber loses air, which is called "spring stroke output moment". In this case, the output moment decreases gradually from 90 degrees to 0 degrees due to the elongation of the spring, as mentioned above. The single-acting actuator is designed on the basis of producing a balancing moment under two conditions. As shown in Figure 11. In each case, by changing the relationship between the number of springs on each side and the pressure of the air source (e.g. two springs on each side and 5.5 bar gas source on each side or vice versa), it is possible to obtain unbalanced moments and obtain two conditions in spring reset application: degassing opening or degassing closing. Under normal working conditions, the recommended safety factor of spring reset actuator is 25-50%.