Speaking of valve actuators, we are currently in contact with electric actuators, pneumatic actuators, hydraulic actuators, electro-hydraulic actuators. What is the difference between the various actuators and what are the advantages and disadvantages of each actuators? That is what we are going to talk today:
Advantages of electric actuator:
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 advantages of electric actuators are high stability and constant thrust that can be applied by users. Electric actuators have great anti-deviation ability, constant output thrust or torque, which can well overcome the unbalanced force of the medium and achieve accurate control of the process parameters, so the control accuracy of electric actuator is higher than that of the pneumatic actuator. If it is equipped with a servo amplifier, it is easy to realize the exchange of positive and negative effects, it is also easy to set the state of the off-signal valve position(in fully open or fully closed), in the event of a fault, it must stay in the original position. That is what the pneumatic actuator can not do, the pneumatic actuator can only stay in the original position with the help of a combined protection system.
Disadvantages of electric actuators:
The main disadvantages of electric actuators are: its structure is more complex and more prone to failure, and because of its complexity, the technical requirements for on-site maintenance personnel are relatively higher, and the operation of the motor will generate heat, if the adjustment is too frequent, it is easy to cause the overheat of the motor, resulting in thermal protection, and at the same time, it will increase the wear of the reduction gear. The other disadvantages of electric actuator is that its operation is low, it takes a long time from the regulator to output a signal to the response of the control valve to move to the corresponding position. This is where the electric actuator is inferior to pneumatic and hydraulic actuators.
Advantages of pneumatic actuator:
Most of the actuators used in control applications are pneumatic actuators, which are more economical than electric and hydraulic actuators, because the pneumatic actuator is using the air as the power source, and it has a simple structure,is easy to operate and maintain. Considering from the view of the maintenance, pneumatic actuators are easier to operate and calibrate than other types of actuators, and they can also be easily interchanged on the spot. The advantages of pneumatic actuator is safety. When using a positioner, it is ideal for flammable and explosive environments, and electric signals have the potential to cause fire hazards due to ignition, if they are not explosion proof or intrinsically safe. Therefore, although the scope of application of electric actuator is becoming wider and wider, in the field of chemical industry, pneumatic actuators still occupy a great advantage.
Disadvantages of pneumatic actuator:
The main disadvantages of pneumatic actuators are: slow response, poor controlling accuracy, and poor anti-deviation ability, which is due to the compressibility of the air, especially when a large pneumatic actuator is used, the time needed for air to fill the cylinder and expelled out is long, but that should not be a problem, because many operating conditions do not require a high degree of control accuracy and extremely fast response, as well as anti-deviation ability.
Advantages of hydraulic actuators:
Hydraulic actuators are usually used on hydraulically controlled butterfly valves and hydraulically controlled ball valves, when great deflection resistance ability, high thrust and fast operating speed are required, hydraulic actuator or electro-hydraulic actuators are often chosen. The thrust generated by the hydraulic actuator can be as high as 225000KGF. Only hydraulic actuators can generate such a large thrust. But the cost of hydraulic actuators is much higher than that of the electric actuators. Because of the incompressibility of liquids, the advantages of hydraulic actuators is better resistance to deflection, which is very important for regulating working conditions, because when the regulating element is close to the valve seat, the throttling condition is unstable. The higher the pressure difference is, the worse the situation is. In addition, the hydraulic actuator can operate very smoothly and respond quickly, so it can achieve high precision control.
Disadvantages of hydraulic actuators:
The main disadvantages of hydraulic actuators is that they are highly expensive, large in size and heavy in weight, and its particularly complicated, and requires specific engineer to take care of. Hydraulic actuators are usually used in some special occasions such as power plants and petrochemicals and relevant technicians should follow up its working conditions.
Summary of electric, pneumatic and hydraulic actuators:
With the development of the industry, electro-hydraulic actuators have also appeared in recent years, that is, the motor, oil pump and electro-hydraulic servo valve are integrated into one, it can work directly as long as the power supply and control signals are connected. The working principle of hydraulic actuator is similar to that of the cylinder, the difference is that the hydraulic actuator can withstand higher pressure than the cylinder. The operating of hydraulic actuator requires an external hydraulic system to support, and the factory needs to be equipped with a hydraulic station and oil pipelines. In contrast, the electro-hydraulic actuator is more convenient.
The advantages and disadvantages of electric actuators, pneumatic actuators and hydraulic actuators are only for reference to customers, when you are select which actuators should be used for your valves. For more details and specific technical parameters, please communicates with our engineer, we can give you a professional and proper advice.