Hydraulic actuators have the highest thrust and are now generally mechatronic, but they are relatively heavy and are therefore rarely used. Electric actuators have poor safety and explosion-proof performance, and the motor is easily damaged when the stroke is blocked or the valve stem is trapped. In recent years, electric actuators are constantly improving and innovating and foreign technologies are cited, so that electric actuators are also commonly used.
Pneumatic actuator has the advantages of simple structure, large output thrust, stable and reliable operation, and safety and explosion-proof. It is widely used in the chemical industry, oil refining and other production processes with high safety requirements.
The actuator and adjustment mechanism of the pneumatic actuator is a unified whole, and the actuator is a film type and a piston type. The piston stroke is long and is suitable for applications where there is a need for high thrust; while the film-type stroke is small and can only directly actuate the valve stem. Because the pneumatic actuator has a simple structure, large output thrust, stable and reliable operation, and a little safety and explosion proof, it has been widely used in the chemical industry, oil refining and other high-security production processes.
Pneumatic mechanisms use compressed air as the working medium to transmit power and control signals. Compared with the hydraulic mechanism has the following advantages:
1. With air as the working medium, it can be directly discharged into the atmosphere after use and it is easy to handle.
2. Quick action, quick response, easy maintenance, clean working media, no media deterioration.
3. The work environment has good adaptability, especially in the flammable, explosive, dusty, strong magnetic, strong vibration, humidity, radiation and temperature changes in the harsh environment, the safety and reliability is better than hydraulic, electronic and Electrical structure.
The inadequacies of the pneumatic structure are: because the air is compressible, the stability of the working speed is slightly poor, but the use of gas-hydraulic linkage device will get satisfactory results; the working pressure is low (usually 0.3 ~ 1.0Mpa), it is difficult Get a lot of output force; noise, in the high-speed exhaust muffler.
The advantages of pneumatic transmission
1. With air as the working medium, the working medium is relatively easy to obtain, and the used air is discharged into the atmosphere, and the handling is convenient. Compared with the hydraulic transmission, it is not necessary to set the recovered oil tank and pipeline .
2. Because the viscosity of air is very small (about one ten-thousandth of the hydraulic oil's dynamic viscosity), its loss is also very small, so it is convenient for centralized gas supply and long-distance transportation. Leakage is not
It will seriously pollute the environment like a hydraulic drive.
3. Compared with the hydraulic transmission, the pneumatic transmission has the advantages of rapid action, quick response, simple maintenance, clean working media, and no media deterioration.
4. The working environment has good adaptability, especially in the flammable, explosive, dusty, magnetic, radiation, vibration and other harsh working environments, superior to hydraulic, electronic, and electrical control.
5. Low cost, overload can automatically protect.
Disadvantages of pneumatic transmission
1. Due to the compressibility of air, the stability of the working speed is somewhat poor. However, the use of gas-liquid linkage devices will achieve satisfactory results.
2. Because the work pressure is low (usually 0.3 ~ 1.0Mpa), and because the structure size should not be too large, the total output force should not be greater than 10 ~ 40KN.
3. The noise is large, and the muffler must be added during high-speed exhaust.
4. The gas signal transmission speed in pneumatic devices is slower than the speed of electrons and light within the speed of sound. Therefore, the pneumatic control system should not be used for complex circuits with too many component levels.
Key considerations for implementing agency selection:
1 reliability;
2 economy;
3 smooth movement and sufficient output force;
4 weight appearance;
5 simple structure, easy maintenance.
Selection of electric actuators and pneumatic actuators
1. The pneumatic actuator is simple and reliable; the poor reliability of the old-fashioned electric actuator is its past weaknesses. However, in the 1990s, the development of electronic actuators completely solved this problem and can be repaired within 5 to 10 years. Its reliability Exceeded pneumatic actuators.
2. Drive source: The biggest deficiency of pneumatic actuators is the need to set up air source stations, which increases the cost; electric actuators are the driving source for anywhere.
3. Thrust and stiffness: Both are equivalent.
4. Piston actuator selection attention:
1 When the thrust of the pneumatic diaphragm actuator is not enough, the piston actuator is used to increase the output force; for large differential pressure regulators (such as medium pressure steam cutoff), when the DN ≥ 200, even the double piston actuator must be selected;
2 For ordinary control valves, piston actuators can also be used to replace the diaphragm actuators. The size of the actuators is greatly reduced. From this point of view, the use of pneumatic piston control valves will be more
3 diagonal stroke type valve, its stroke adjustment mechanism, the typical structure is a double piston gear rack rotation type. The most worthy of emphasis is the traditional "straight stroke piston actuator + angle iron + crank connecting rod" mode.
