What Is a Pneumatic Linear Actuator?

Pneumatic actuator is an actuator that uses air pressure to drive the opening and closing or regulating valve. It is also called a pneumatic actuator or a pneumatic device, but it is generally called a pneumatic head. Pneumatic actuators are sometimes equipped with certain auxiliary devices. Commonly used are valve positioners and handwheel mechanisms. The role of the valve positioner is to use the feedback principle to improve the performance of the actuator, so that the actuator can achieve accurate positioning according to the control signal of the controller. The role of the hand wheel mechanism is to control the control valve directly when the control system is out of power, gas, controller output or actuator failure, in order to maintain normal production. ^[1]

Pneumatic actuators

Pneumatic actuator is an actuator that uses air pressure to drive the opening and closing or regulating valve. It is also called a pneumatic actuator or a pneumatic device, but it is generally called a pneumatic head. Pneumatic actuators are sometimes equipped with certain auxiliary devices. Commonly used are valves

1.The rated output force or torque of the pneumatic device should meet the requirements of GB / T12222 and GB / T12223

1. There must be no scratches, cuts, air holes, burrs, etc. on the end cover, end flange and box of the casting cylinder.

1. Receive continuous air signal and output linear displacement (continuous electrical signal can also be received after power-on / gas conversion device), and some can output angular displacement when equipped with a rocker arm.

Pneumatic actuators

2. It has positive and negative function.

3. The moving speed is large, but the speed will become slower when the load increases.

4. The output force is related to the operating pressure.

5. High reliability, but the valve cannot be maintained after the gas source is interrupted (it can be maintained after adding a retention valve).

6. It is inconvenient to implement segmented control and program control.

7. Simple maintenance and good adaptability to the environment.

8. The output power is large.

9. With explosion-proof function.

Compact double-piston gear, rack-type structure, precise meshing, high efficiency, and constant output torque.

The aluminum cylinder block, piston and end cover are the lightest compared to actuators of the same structure.

The cylinder body is made of extruded aluminum alloy and hard anodized. The inner surface has a hard texture, high strength and high hardness. Sliding bearings made of low-friction materials avoid direct contact between metals, low friction coefficient, flexible rotation, and long service life.

The installation and connection dimensions of pneumatic actuators and valves are designed according to international standards ISO5211, DIN3337 and VDI / VDE3845, which can be interchanged with ordinary pneumatic actuators.

The air supply hole conforms to NAMUR standard.

The bottom shaft mounting hole of the pneumatic actuator (in accordance with ISO5211 standard) is double square, which is convenient for the valve with a square rod to be installed linearly or at a 45 ° angle.

The top and top holes of the output shaft comply with NAMUR standards.

The adjusting screws at both ends can adjust the opening angle of the valve.

The same specifications are double acting and single acting (spring return).

You can choose the direction according to the needs of the valve, and rotate it clockwise or counterclockwise.

Install according to user needs

The control accuracy is low, and the double-acting pneumatic actuator cannot return to the preset position after the air source is disconnected. Single acting pneumatic actuator, it can return to the preset position by spring after the air source is cut off

Actuators are divided into three categories according to their energy forms: pneumatic, electric and hydraulic. They have their own characteristics and are suitable for different occasions. Pneumatic actuators are a category of actuators. Pneumatic actuators can also be divided into two types: single-acting and double-acting: the switching action of the actuator is driven by the air source, which is called DOUBLE ACTING (double acting). SPRING RETURN (single

Double acting actuator

The selection of double acting actuators is based on DA series pneumatic actuators. The output torque of the rack and pinion actuator is obtained by multiplying the piston pressure (supplied by the air source pressure) by the pitch circle radius (force arm), as shown in Figure 4. And the friction resistance is small and the efficiency is high. As shown in Fig. 5, the output torque is linear when rotating clockwise and counterclockwise. Under normal operating conditions, the recommended safety factor for double acting actuators is 25-50%

Single acting actuator

Selection of Mingjing single-acting actuator Take the SR series pneumatic actuator as an example. In the application of spring return, the output torque is obtained during two different operations. According to the stroke position, each operation generates two different torque values. . The output torque of the spring return actuator is obtained by multiplying the force (air pressure or spring force) by the force arm. The output torque is obtained after the air pressure enters the middle cavity compression spring, which is called "air stroke output torque". In this case, the pressure of the air source forces the piston to turn from 0 degrees to 90 degrees. Due to the reaction force generated by the compression of the spring, the torque gradually decreases from the maximum at the starting point to the second condition: the output torque is the spring recovery when the cavity is out of air The force acting on the piston is called "spring stroke output torque". In this case, due to the extension of the spring, the output torque gradually decreases from 90 degrees to 0 degrees. As described above, the single-acting actuator is based on the two It is designed on the basis of a balanced moment under these conditions. As shown in Figure 11. In each case, by changing the relationship between the number of springs on each side and the air supply pressure (such as 2 springs on each side and 5.5 bar air supply or vice versa), it is possible to obtain unbalanced torque. Two conditions can be obtained in spring return applications : Out of air or off of air. Under normal operating conditions, the recommended safety factor for spring-return actuators is 25-50%

Selection example of spring return actuator (see also technical data sheet):

Spring off (out of air)

* Torque of ball valve = 80NM

* Safety factor (25%) = 80NM + 25% = 100NM

* Air source pressure = 0.6MPa

The selected SY-SR actuator is SR125-05 because the following values can be generated:

* Spring stroke 0o = 119.2NM

* Spring stroke 90o = 216.2NM

* Air stroke 0o = 228.7NM

* Air stroke 90o = 118.8NM

In terms of technical performance, the advantages of pneumatic actuators mainly include the following 4 aspects:

(1) The load is large, which can adapt to the application of high torque output.

(2) Quick action and quick response.

(3) The working environment has good adaptability, especially in harsh working environments such as flammable, explosive, dusty, strong magnetism, radiation and vibration, which is superior to hydraulic, electronic and electrical control.

(4) The motor is easily damaged when the stroke is blocked or the valve rod is tied.

The advantages of electric actuators include:

(1) Compact structure and small size. Compared with pneumatic actuators, electric actuators have a relatively simple structure. A basic electronic system includes an actuator, a three-position DPDT switch, a fuse and some wires, which is easy to assemble.

(2) The drive source of the electric actuator is very flexible. Generally, the vehicle power supply can meet the needs, while the pneumatic actuator needs the air source and the compression drive device.

(3) The electric actuator has no danger of leakage and high reliability, and the compressibility of air makes the stability of the pneumatic actuator slightly worse.

(4) No need to install and maintain various pneumatic pipelines.

(5) The load can be maintained without power, and the pneumatic actuator needs a continuous pressure supply.

(6) Since no additional pressure device is required, the electric actuator is quieter. Generally, if the pneumatic actuator is under a heavy load, a silencer is added.

(7) In a pneumatic device, it is usually necessary to convert an electrical signal into a gas signal and then into an electrical signal. The transmission speed is slow, and it is not suitable for complex circuits with too many component stages.

(8) Electric actuators are superior in terms of control accuracy.

In fact, pneumatic and electric systems are not mutually exclusive. Pneumatic actuators can simply realize fast linear circular motion, simple structure, convenient maintenance, and can be used in various harsh working environments, such as explosion-proof requirements, dusty or humid conditions. However, in the case where the force increases rapidly and precise positioning is required, an electric drive with a servo motor has advantages. For applications that require precise, synchronous operation, adjustable and specified positioning programming, an electric drive is the best choice. An electric drive system consisting of a servo or stepper motor with a closed-loop positioning controller can supplement the deficiencies of pneumatic systems. Office.

Various systems in modern control are becoming more and more complex and sophisticated, and it is not a certain drive control technology that can meet the various control functions of the system. Electric actuators are mainly used in applications that require precise control. The requirements for flexibility in automation equipment are constantly increasing. The same equipment is often required to meet the processing needs of workpieces of different sizes. The actuators need to be controlled at multiple points. The precise control or synchronous tracking of running speed and torque can not be achieved with traditional pneumatic control, and electric actuators can easily achieve such control. It can be seen that pneumatic actuators are more suitable for simple motion control, while electric actuators are mostly used for precision motion control.