valve-electric,-pneumatic,-hydraulic,-electro-hydraulic-drive-mode-analysis-and-comparison

 In the fields of environmental protection, water conservancy, petrochemical, metallurgy, papermaking, electric power, aerospace, pipeline, industrial equipment, industrial processing and other fields, a large number of valves are needed to control fluid movement. The drive device that controls the opening, closing or partial switch of the valve is usually called a valve actuator or a valve driver. As the terminal actuator of valve control, the reliability, controllability and function of the actuator will directly affect the success or failure of adjustment and control results and the safety of equipment, and restrict the improvement of the overall level of automation.

Traditional actuators are divided into three types: electric, pneumatic and hydraulic, and the derived gas-liquid combination and electro-hydraulic combined drive. Each type of drive has its own advantages and disadvantages. This article briefly explains the advantages and disadvantages of electric, pneumatic and hydraulic drives for everyone to quickly understand.

1.Electric actuator

Electric actuators, as the name implies, are powered by electricity, using single-phase or three-phase motors to drive gears or worm gears to output linear or rotary motion. The electric actuator can output a relatively constant driving force, has strong anti-deviation ability, and has higher control accuracy than the pneumatic actuator, and can automatically maintain its position without the aid of other auxiliary systems. Electric actuators have the characteristics of simple operation and easy remote control. However, their structure is complex, and they are prone to failure due to load. There are often low positioning accuracy, over-opening and closing, motor burnout, gear box wear, etc., and the maintenance cost is high. Too frequent adjustment will cause the motor to heat up, and the reduction gear will be easily worn. In addition, the electric actuator runs slowly, it is difficult to achieve a large driving force, and there are problems such as difficulty in realizing over-protection and poor position.

2.Pneumatic actuator

The pneumatic actuator is powered by compressed air and has the characteristics of simple structure and convenient maintenance, but it is large in size and requires an air source and an air purification device; the actuator and adjustment mechanism of the pneumatic actuator are a unified whole, and its actuator has a thin film Type, piston type, fork type and rack and pinion type. Using gas as the power medium has the advantages of high safety and low requirements for the use environment. However, due to the compressibility of gas, pneumatic actuators with relatively low stiffness have slow response, poor resolution, low control accuracy, and weak anti-deviation ability. Undesirable vibration of the device. In addition, the power-to-weight ratio is poor, the power density is low, and the pneumatic actuator with a large driving force is extremely complex, heavy and expensive.

3.Hydraulic actuator

Ordinary hydraulic actuators are powered by high-pressure oil and have the characteristics of large load capacity and high adjustment accuracy, but they need to be equipped with huge independent oil supply equipment, and the maintenance workload is relatively large. Rack type, screw type actuator. All three have advantages and disadvantages. The vane type structure has a small bearing capacity and a lot of oil leakage; the rack and pinion type has a large bearing capacity, a simple structure, a large volume, accurate screw positioning, and high processing difficulty. The figure below shows the rack and pinion actuator mounted on the valve. Existing hydraulic actuators usually need to be matched with a hydraulic station, resulting in large volume, long hydraulic pipelines, large throttling losses, and inconvenient maintenance.

4.Electro-hydraulic actuator

As a power device derived from hydraulic actuators, electro-hydraulic actuators integrate hydraulic, control, electromechanical, computer, communication and other technologies, and can accurately control the position of the controlled object quickly and stably, and are used in various valves. Drive and control. The electro-hydraulic actuator integrates the hydraulic power module and the control module. The electro-hydraulic actuator integrates the simple electric operation, fast hydraulic power, and reliable electric control board, and has the advantages of fast response speed, high control precision, large output power, and compact structure; at the same time, the electro-hydraulic actuator overcomes the pneumatic actuator. The control accuracy is low, the controllability of the electric actuator is poor and so on. Electro-hydraulic actuators can be roughly divided into two types: one is the servo valve control type, that is, the traditional electro-hydraulic servo actuator, which adopts an open hydraulic system, and adjusts the flow direction and flow rate of hydraulic oil by controlling the servo valve, so as to realize the control of the hydraulic oil. The adjustment of the controlled object; one is the motor control type, which adopts a closed hydraulic system to control the output direction and flow of the pressure oil of the two-way pump by adjusting the steering and speed of the stepper motor or servo motor. Precise control of the controlled object.

The new electro-hydraulic actuator has the advantages of simple structure, compactness, small size, stable transmission, large output torque, convenient speed adjustment, easy control, and easy overload prevention. Features.

The hydraulic micro-power unit and control board are integrated in the control box, making the entire actuator intelligent and miniaturized. Electro-hydraulic actuator is an important control element of industrial automatic control system, which can adjust valve pressure, flow, temperature, etc., and is widely used in chemical, petroleum, metallurgy, electric power, coal and other industrial process control systems. The development of electro-hydraulic actuators is developing towards the trend of small size, light weight, high efficiency and energy saving, and high reliability.

The general principle for the correct selection of the valve drive device is: the operating characteristics of the drive device are required to be consistent with the operating characteristics of the valve. For valves that do not require automatic control, a manual drive device is optional; a valve that needs to be opened and closed quickly can be equipped with a pneumatic or pneumatic-hydraulic linkage drive device; a valve that needs automatic control or remote control can be equipped with an electric drive device; On flammable and explosive pipelines, if an electric device is selected, an explosion-proof electric drive device should be selected.