The selection of a certain actuator type depends on the application requirements and restrictions and on cost constraints of the system. The type of actuators compared are hydraulic, pneaumatic and electrical.
In this qualitative comparison not the maximum achievable performances, but rather the standard widely available ones are compared.
The hydraulic actuators are best suited for high forces and torques, followed by the electric actuators.
An important characteristic property of an actuator is the force density (force/volume or force/weight). The highest force density is inherent in the hydraulic actuators. However, if the volume(weight) of the motor, the pump and other necessary components are taken into consideration, electric actuators offer almost the same or even higher force density. In applications where number of actuators are required, hydraulic system with a central pump station is frequently more economical solution. Electric actuators have the highest energy efficiency. Hydraulic and pneumatic systems frequently need continuously running pumps or compressors, even though the actuator is not performing any motion.
Due to the compressibility of the gas or fluid and because of the less exact control characteristics of the hydraulic and pneumatic valves, the positioning accuracy of the hydraulic and pneumatic actuators is lower than the electric systems. Some servo hydraulic or servo pneumatic systems can reach a fairly high positioning accuracy and good repeatability but cannot reach the performance of pure electric or electromechanical systems. The costs of servo hydraulic system are usually considerably higher than the costs for a same performance electric actuator. There is practically no environmental hazard associated with electric actuators; on the other hand, the hydraulic systems constitute a constant danger due to the possible leakage of hydraulic fluid. The electric actuators feature the most balanced overall performance. The increased performance, reliability and affordability of state of the art motors and electronic motion controls gives a strong boost for the electric actuators. In countless automation applicatlons, where about a decade ago only hydraulic or pneumatic actuators were used, electric actuators are taking over the field. There are still a number of high force density requiring applications where the hydraulic actuator is a better choice.The developments in the servo hydraulic and servo pneumatic field helped to improve the positioning accuracy and control capability of these types of actuators. Despite this, the utilization of electric actuators is growing more rapidly and this tendency will most likely continue or even accelerate.