How to choose proper pneumatic actuator for a butterfly valve?

Pneumatic actuators are often installed on butterfly valves as actuators to greatly improve their working efficiency. So how can we make the correct choose of pneumatic actuators?
A. Air source pressure or power supply voltage of the actuator;
B. The operating torque of the butterfly valve plus the safety factor recommended by the manufacturer (according to the operating conditions);
C. The type of pneumatic actuator, double-acting or single-acting (spring return) and the output torque under a certain air source or the output torque under the rated voltage;
D. Its steering and failure mode (fault on or fault off) is very important to correctly choose an actuator. If the actuator is too large, the valve stem may be overstressed. On the contrary, if the actuator is too small, the side cannot generate enough torque to fully operate the valve. The torque required to operate the valve comes from the friction between the metal parts of the valve and the seal. According to the valve application occasion, operating temperature, operating frequency, pipeline and pressure difference, flowing medium (lubrication, drying, mud), many factors affect the operating torque.