Before specifying pneumatic actuators or electric actuators for valve automation, it is important to consider several key characteristics of each.
Electric actuators are most commonly capable of using a 25% motor duty cycle. This means that the motor must be shut down frequently to prevent overheating at high duty cycles. Since 95% of the operating time of most automatic opening and closing valves is not used, the duty cycle is generally not a problem. Electric motors with suitable motors and capacities are upgraded to 100% duty cycle.
Pneumatic actuators can be stopped indefinitely without overheating. The electric actuator shall not be stopped. Stalling the electric actuator can cause the motor to generate heat and cause excessive current, which can lead to damage. To protect the device, a torque switch or a thermal sensor and a current sensor are installed in the electric actuator.
The ability to control pneumatic actuator speed is an important benefit of the design. The simplest way to control the speed is to install a variable orifice (needle valve) in the actuator at the air pilot exhaust.