A rotary cylinder is an actuator that uses compressed air as a power source, and its core function is to achieve a specific rotation angle or continuous rotation motion. Its internal structural design enables the air pressure energy to be efficiently converted into a mechanical output in the form of rotation, generating a controllable rotation torque. The essence of this device is to provide a pneumatically driven rotational power solution, which is suitable for occasions that require precise angle positioning or continuous rotation drive but do not require a large range of circular motion. It plays a key role in the automation process, converting the instructions of the pneumatic control system into reliable rotational motion output, and is one of the basic driving force units to achieve a specific action sequence or drive a rotating component. Its value lies in providing a relatively compact and responsive way to achieve pneumatic rotation motion.