The actuators mainly include electric actuators, pneumatic actuators and hydraulic actuators:
1. Electric Actuators: Electric actuators are mainly used in power plants or nuclear power plants because a smooth, stable and slow process is required in high pressure water systems. The main advantage of the electric actuator is the high stability and the constant thrust that the user can apply. The anti-deviation ability of the electric actuator is very good, and the thrust or torque of the output is basically constant, which can well overcome the medium. Balanced force, accurate control of process parameters, so control accuracy is higher than pneumatic actuators. If a servo amplifier is used, it is easy to achieve the exchange of positive and negative effects, and it is also easy to set the state of the off-signal valve position (hold/full-open/full-off), and when it is faulty, it must stay in place, this is Pneumatic actuators do not, pneumatic actuators must be secured by means of a combined protection system.The shortcomings of electric actuators are: the structure is more complicated, it is more prone to failure, and because of its complexity, the technical requirements for on-site maintenance personnel are relatively higher; the motor runs to generate heat, if the adjustment is too frequent, it is easy to cause The motor overheats, generates thermal protection, and also increases the wear on the reduction gear; in addition, it runs slower, and it takes a long time to output a signal from the regulator to move to the corresponding position in response to the valve response. It is not as good as pneumatic and hydraulic actuators.
2. Pneumatic Actuator: Most of the actuators used in today's industrial control are pneumatic actuators. Because of the power of the air source, it is economical and economical compared to electric and hydraulic, and the structure is simple and easy to grasp and maintain. From a maintenance point of view, the pneumatic actuator is easier to operate and calibrate than other types of actuators, and it is also easy to achieve positive and negative interchanges in the field. Its greatest advantage is safety. When using a positioner, it is ideal for flammable and explosive environments, and if the electrical signal is not explosion-proof or intrinsically safe, there is a potential risk of fire due to fire. Therefore, the application range of electric control valves is now wider and wider. However, in the chemical industry, pneumatic control valves still occupy an absolute market advantage.The main disadvantages of pneumatic actuators are: slow response, poor control accuracy, and poor resistance to deviation, due to the compressibility of the gas, especially when using large pneumatic actuators,air filling cylinders and emptying time. But this should not be a problem, as high levels of control accuracy and extremely fast response and resistance to deviation are not required in many operating conditions.
3. hydraulic actuator: When the need for abnormal anti-deviation ability and high thrust and rapid formation speed, we often choose hydraulic or electro-hydraulic actuators. Because of the incompressibility of the liquid, the advantage of using a hydraulic actuator is the superior resistance to deflection, which is important for adjusting the operating conditions, because the throttling condition is unstable when the adjusting element is close to the valve seat, the more The pressure difference is large, and the situation is more severe. In addition, the hydraulic actuator operates very smoothly and responds quickly, so high-precision control can be achieved. The electro-hydraulic actuator integrates the motor, oil pump and electro-hydraulic servo valve. It can work by connecting the power supply and control signals. The hydraulic actuator is similar to the cylinder, but it can withstand higher pressure than the cylinder. The work requires an external hydraulic system, and the plant needs to be equipped with a hydraulic station and a delivery line. In contrast, an electro-hydraulic actuator is more convenient.
The main disadvantages of hydraulic actuators are the high cost, the bulky and bulky physical examination, the special complexity and the need for special engineering, so most of them are used in some special occasions such as power plants and petrochemicals.