Pneumatic, electric, hydraulic actuator comparison, quick reference that
Comparison of pneumatic, electric and hydraulic actuators
The actuators used in the control valve are no more than pneumatic, electric and hydraulic (electro-hydraulic), and their performance has its own advantages and disadvantages, which are described below.
1. Pneumatic actuator: at present, most of the actuators used in industrial control occasions are pneumatic actuators. Compared with electric and hydraulic actuators, pneumatic actuators are more economical, simple and easy to master and maintain. From the point of view of maintenance, the pneumatic actuator is easier to operate and calibrate than other types of actuators, and can be easily interchanged in the field. Its great advantage is safety. When the locator is used, it is ideal for flammable and explosive environment. If the electric signal is not explosion-proof or intrinsically safe, there is a potential fire risk caused by ignition. Therefore, the application range of electric control valve is more and more wide. But in the field of chemical industry, pneumatic control valve still occupies the market advantage.
The main disadvantages of pneumatic actuator are: slow response, poor control accuracy, poor anti deviation ability, which is due to the compressibility of gas, especially when using large pneumatic actuator, it takes time for air to fill the cylinder and empty. But this should not be a problem, because many conditions do not require a high degree of control accuracy and extremely fast response and anti deviation ability.
2. Electric actuator: electric actuator is mainly used in power plant or nuclear power plant, because a smooth, stable and slow process is required in high-pressure water system. The main advantages of electric actuator are high stability and constant thrust that can be applied by users. The thrust generated by large actuator can be as high as 225000kgf. Only hydraulic actuator can achieve this thrust, but the cost of hydraulic actuator is much higher than that of electric actuator. The anti deviation ability of electric actuator is very good, and the output thrust or torque is basically constant, which can overcome the unbalanced force of medium and achieve the accurate control of process parameters, so the control accuracy is higher than that of pneumatic actuator. If equipped with a servo amplifier, it is easy to realize the exchange of positive and negative effects, and also can easily set the off signal valve position state (hold / full open / full close). When the fault occurs, it must stay in the original position, which is impossible for the pneumatic actuator. The pneumatic actuator must rely on a set of combined protection system to realize the position protection.
The main disadvantages of the electric actuator are: the structure is more complex, more prone to failure, and due to its complexity, the technical requirements for on-site maintenance personnel are relatively higher; the motor operation to generate heat, if the adjustment is too frequent, it is easy to cause motor overheating, thermal protection, but also increase the wear of the reduction gear; in addition, the operation is slow, from the regulator It takes a long time for the control valve to respond and move to the corresponding position, which is not as good as pneumatic and hydraulic actuators.
3. Hydraulic actuator: when we need abnormal anti deviation ability, high thrust and fast forming speed, we often choose hydraulic or electro-hydraulic actuator. Because of the incompressibility of the liquid, the advantage of using the hydraulic actuator is the better anti deviation ability, which is very important for the regulating condition, because when the regulating element is close to the valve seat, the flow condition is unstable. The greater the pressure difference is, the more severe the situation is. In addition, the hydraulic control mechanism is very fast and can realize high dynamic response. The electro-hydraulic actuator integrates the motor, oil pump and electro-hydraulic servo valve into one. As long as the power supply and control signal are connected, the hydraulic actuator can work. However, the hydraulic actuator is similar to the cylinder, but it can withstand higher pressure than the cylinder. Its work requires external hydraulic system. The factory needs to be equipped with hydraulic station and oil pipeline. In contrast, the electro-hydraulic actuator is more convenient.
The main disadvantages of hydraulic actuator are high cost, huge and bulky physical examination, especially complex and need special engineering, so most of them are used in some special occasions such as power plant and petrochemical industry.
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