4. Calculation of total friction torque The friction torque of the valve is calculated according to the following formula: MF=MQZ+MFT+MFC (N-M) (4), where: friction torque of MQ ball in the valve seat; Friction torque between MFT packing and valve rod; Friction torque analysis of MFC valve stem head The force generated by pneumatic ball valve shows that under the action of medium, the floating ball moves towards the outlet end, and the force generated is all borne by the valve seat seal ring at the outlet. The valve seat seal ring in front of the ball does not bear the force and does not affect the friction torque.

4. The pneumatic control valve of the boiler uses single-phase AC pneumatic actuator as servo pneumatic actuator. There are two weaknesses of single-phase AC pneumatic actuator. 1. Single motor is started in capacitive split phase mode. The starting torque is relatively small, but the starting current of 2 single machine pneumatic motors with speed regulation function is very large. Frequent operation of nearly 7 times of rated current will make the motor always in the working state of high current, which will lead to motor burning when the motor heats seriously. Measures taken for pneumatic control valve