Detailed explanation of the working principle of pneumatic actuators and comparison with electric actuators

Overview of pneumatic actuators

Pneumatic actuator, as a device operated by compressed air, converts air pressure into linear or angular displacement to provide execution power for valves. It is usually referred to as pneumatic actuator or pneumatic device, and is more commonly referred to as pneumatic head in daily life. This actuator integrates the actuator and the regulating mechanism into a whole, and its actuator forms are diverse, including membrane type, piston type, fork type, and gear rack type. It can continuously receive air signals and output linear displacement. When combined with a rocker arm, it can also output angular displacement. Although it moves rapidly, its speed slows down correspondingly when the load increases. Pneumatic actuators have excellent reliability, but if there is no holding valve to maintain their position after a gas source interruption, the valve will not be able to maintain its original position. In addition, it also supports segmented control and program control, and has explosion-proof function.

The advantages of pneumatic actuators include a wide range of power sources, rapid transmission, high safety, and simple maintenance. However, it also has some drawbacks, such as limited output force, complex control system, and energy waste.

1. Working principle of pneumatic actuator

1.1. Transmission principle of pneumatic actuator

The work of pneumatic actuators is to control the opening and closing of valves by driving the piston movement through compressed air. When compressed air enters the pneumatic actuator through nozzle A, the gas will push the double piston to move linearly towards the cylinder head end. This causes the rack on the piston to drive the gear on the rotating shaft to rotate counterclockwise by 90 degrees, thereby opening the valve. At this point, the gas at both ends of the pneumatic actuator valve is discharged through nozzle B. On the contrary, if compressed air enters the two ends of the actuator from nozzle B, the gas will push the double plug to move in a straight line towards the middle, and the rack will drive the gear to rotate clockwise by 90 degrees, closing the valve. At this point, the gas in the middle is discharged through nozzle A.

1.2. Classification and application of executing agencies

Pneumatic actuators are the core components in pneumatic systems, responsible for converting pneumatic pressure into linear or angular displacement. Common types of actuators include diaphragm and piston, each with different torque outputs and application scenarios. Thin film actuators are widely used due to their simple structure, affordable price, and convenient maintenance; The piston type actuator is known for its powerful output force and is suitable for situations that require high thrust or torque.

1.3. Components of Control Mechanism

The control mechanism, also known as the control valve, is a throttling element whose local resistance can be adjusted by changing it. The components such as the actuator, valve core, valve stem, and upper and lower valve covers are adapted to different usage needs through their different structures and materials.

1.4. Construction and types of control valves

The construction forms of control valves are diverse, and their core lies in the design of the valve core, with straight stroke and angular stroke valve cores as the core, to achieve different flow control characteristics. Common straight stroke valve cores include flat plate type, plunger type, etc., while angular stroke valve cores adjust the flow cross-section through rotational motion. Common types include eccentric rotary valve cores, butterfly valve cores, and spherical valve cores.

2. Functions and principles of electrical converters

2.1. Comparison between Electrical Converter and Gas Electric Converter

The electrical converter converts electrical signals into pressure signals through the principle of force balance, and adapts to different automatic adjustment systems. Similar to gas electric converters, both operate based on the principle of force balance, with the core of converting the standard DC signal of electric instruments into the standard pressure signal of pneumatic instruments.

2.2. Application of Electrical Converter

Electrical converters play a crucial role in the automatic regulation system of electric unit combination instruments, especially in control systems that require stability and reliability. They convert electrical signals into pressure signals to achieve automatic regulation.

3.The Importance of Electrical Valve Positioners

3.1. Working principle of electrical valve positioner

The electrical valve positioner receives signals and provides feedback to control the regulating valve, forming a closed-loop feedback control system. It uses valve stem displacement as feedback measurement signal to ensure the positioning accuracy of the regulating valve.

3.2. Function of Electrical Valve Positioner

Electric valve positioners can improve the positioning accuracy of regulating valves, especially when dealing with complex conditions such as high temperature and high pressure. In addition, it can overcome the resistance of the medium to the movement of the valve stem and improve the output thrust of the actuator.

3.3. Classification of Electrical Valve Positioners

Electrical valve positioners can be divided into pneumatic valve positioners, electrical valve positioners, and intelligent electrical valve positioners based on different input signals to meet different application requirements and accuracy requirements.

4. Comparison between pneumatic and electric actuators

4.1. Comparison of advantages and disadvantages between pneumatic and electric actuators

Pneumatic actuators are suitable for situations that require strong operating force and fast response, while electric actuators are suitable for high-precision and complex control scenarios. The former has the advantages of simple structure, easy maintenance, and adaptability to harsh conditions, while the latter is known for its high precision and flexible driving source.

4.2. Applicability in different scenarios

In some industrial applications that require high control accuracy and speed, electric actuators have more advantages. Pneumatic actuators are often the ideal choice for automation equipment due to their fast response and high adaptability. Therefore, when choosing, it is necessary to weigh the advantages and disadvantages of each actuator based on specific needs.