How the German BAR pneumatic actuator works The German BARGmbh was founded in 1979 in Dattenberg, an industrial city in western Germany. Since its inception, BAR has been dedicated to the development and production of pneumatic actuators and solenoid valves and other related pneumatic components in the industrial field. It has modern fully automated factories and many years of experience in the production of pneumatic products.
German BAR is a pioneer in the field of self-controlled valves:
In 1981, BAR took the lead in proposing the principle of using rack and pinion, using dual pistons and safety springs to drive the shaft of the actuator. This idea was followed by the world's major manufacturers and was eventually adopted worldwide.
Pneumatic Actuators Pneumatic actuators are actuators that use air pressure to actuate the opening and closing or adjustment of valves. They are also called pneumatic actuators or pneumatic devices, but are generally known as pneumatic heads.
Pneumatic actuator actuator and adjustment mechanism is a unified whole, and its implementing agencies are film, piston, fork-type and rack and pinion 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. The fork type pneumatic actuator has the characteristics of large torque, small space, and the torque curve more consistent with the torque curve of the valve, but is not very beautiful; it is often used on valves with large torque. Rack and pinion type pneumatic actuators have the advantages of simple structure, stable and reliable operation, and safety and explosion proof. They are widely used in power plants, chemical industry, oil refining and other high-security production processes.
Chinese name pneumatic actuator foreign name Pneumaticactuators
Working principle When the compressed air enters the pneumatic actuator from the A nozzle, the gas pushes the double piston to the two ends (cylinder head end) and moves linearly. The rack on the piston drives the gear on the rotary shaft to rotate 90 degrees counterclockwise, the valve is Was opened. At this point, the gas at both ends of the pneumatic actuator valve discharges with the B nozzle. Conversely, when the compressed air enters both ends of the pneumatic actuator from the B officer's nozzle, the gas pushes the double plugs toward the middle of a straight line. The rack on the piston drives the gear on the rotary shaft to rotate 90 degrees clockwise, and the valve is closed. At this moment, the gas in the middle of the pneumatic actuator discharges with the A nozzle. The above is the standard transmission principle. According to the user's requirements, the pneumatic actuator can be equipped with a transmission principle that is the opposite of the standard type. That is, the selective axis rotates clockwise to open the valve and counterclockwise to close the valve. Single-acting (spring return type) pneumatic actuator A nozzle for the inlet, B nozzle for the exhaust hole (B nozzle should be installed muffler). The inlet of the A nozzle is to open the valve. When the air is cut off, the valve is closed by spring force.
The basic structure of the editing internal structure of the pneumatic actuator actuator type and structure are roughly the same, mainly different actuators. Therefore, when the pneumatic actuator is introduced, it is divided into an actuator and a regulating valve. Pneumatic actuator consists of two parts: the actuator and the regulating valve (adjusting mechanism). According to the size of the control signal, a corresponding thrust is generated to push the regulating valve. The regulating valve is the regulating part of the pneumatic actuator. Under the action of the actuator thrust, the regulating valve generates a certain displacement or rotation angle and directly regulates the flow of the fluid.
1. Pneumatic devices are mainly composed of cylinders, pistons, gear shafts, end caps, seals, screws, etc.; complete sets of pneumatic devices should also include opening indication, stroke limit, solenoid valve, positioner, pneumatic components, manual mechanism, signal Feedback and other components.
2. The connection size of pneumatic devices and valves shall comply with the requirements of ISO5211 (bottom), GB/T12222 and GB/T12223.
3, pneumatic device with manual mechanism, in the gas source is interrupted, it should be able to use its manual mechanism to open and close the pneumatic ball valve, facing the hand wheel, the hand wheel or handle should be counterclockwise rotation for the valve to open, clockwise rotation for Valve off.
4. When the end of the piston rod is internally or externally threaded, the spanner wrench should be used for standard wrenches.
5, the piston seal ring should be easy to replace and repair.
6, the pneumatic device with a buffer mechanism, the stroke length of the buffer mechanism can refer to the "Table 1" provisions.
7. Pneumatic devices with adjustable buffer mechanisms shall have mechanisms for external adjustment of the buffering action of the cylinder.
8. The thread size of the air inlet and outlet of the cylinder should meet the requirements of MANURNORM (accessory standard) sypv, GB/T7306.1, GB/T7306.2 and GB/T7307.
The working principle of the German BAR pneumatic actuator performance editor 1, pneumatic device rated output force or torque should be consistent with the provisions of GB/T12222 and GB/T12223 above for the film-type actuator 2, under no-load conditions, the cylinder input according to " The air pressure specified in Table 2 shall be stable and free of jamming and crawling.
3. Under the air pressure of 0.6MPa, the output torque or thrust of the pneumatic device starting and closing in both directions shall not be less than the value indicated by the label of the pneumatic device, and the action shall be flexible, and permanent deformation of each part shall not be allowed. Other abnormalities.
4. When the seal test is conducted with the maximum working pressure, the leakage of air from the respective back pressure side must not exceed (3+0.15D)cm3/min (standard state); leakage from the end cap and output shaft is not allowed. The air volume must not exceed (3+0.15d)cm3/min.
5, strength test with 1.5 times the maximum working pressure test, to maintain the test pressure 3min, the cylinder end cover and static seal parts do not allow leakage and structural deformation.
6, the number of operating life, pneumatic device simulation of pneumatic valve action, in the case of maintaining the output torque or thrust in both directions, the opening and closing of the opening and closing operation should not be less than 50,000 times (start-closed cycle for a).
7. Pneumatic device with buffer mechanism, when the piston moves to the stroke end position, no impact phenomenon is allowed.
Appearance editing 1. End caps, end flanges, and boxes of casting cylinders must be free of scratches, cuts, air holes, and burrs.
2. The paint coating or chemical treatment layer on the outer surface of the pneumatic device should be flat, smooth, uniform in color, free of oil, indentation and other mechanical damage.
Advantage editing 1, receiving a continuous gas signal, output linear displacement (after the power / gas conversion device, you can also receive continuous electrical signal), and some with rocker, you can output the angular displacement.
Pneumatic actuator 2, a positive and negative function.
3, moving speed, but the speed will slow down when the load increases.
4, the output force and operating pressure.
5, high reliability, but the valve can not be maintained after the gas source is interrupted (can be maintained after adding the valve).
6. Inconvenient to realize segmented control and program control.
7, maintenance is simple, good adaptability to the environment.
8, the output power is larger.
9, with explosion-proof function.
Compact double piston gear, rack-type structure, precise meshing, high efficiency, constant output torque.
Aluminum cylinders, pistons and end caps are lightest in weight compared to actuators of the same size.
The cylinder body is an extruded aluminum alloy and hard anodized. The inner surface has a hard texture and high strength and hardness. The use of low-friction materials made of sliding bearings, to avoid direct contact between the metal, low friction coefficient, flexible rotation, long service life.
Pneumatic actuator and valve installation and connection dimensions are designed according to the international standards ISO5211, DIN3337 and VDI/VDE3845 and can be interchanged with common pneumatic actuators.
The gas source hole meets the NAMUR standard.
Pneumatic actuator bottom shaft assembly holes (according to ISO5211 standard) are double quadrilateral, easy to install with linear valve or 45° corner of the valve with square bar.
The top and top holes in the output shaft meet the NAMUR standard.
The adjusting screws at both ends can adjust the opening angle of the valve.
The same specifications are double acting, single acting (spring return).
According to the valve needs to choose the direction, clockwise or counterclockwise rotation.
According to user needs to install the solenoid valve, positioner (degree of opening instructions), reply, all kinds of limit switches and manual operation device.
Disadvantages The low precision of editing and control, dual-acting pneumatic actuator, can not return to the preset position after the air source is cut off. Single Acting Pneumatic Actuator, After Air Supply Can Rely On The Spring Back To Presume Category Selection Editor According to its energy form, it can be divided into three categories: 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 categorized into single-acting and double-acting types: The actuator's switching action is driven by the air source and is called DOUBLE ACTING (double acting). The SPRINGRETURN (single acting) switch action is air driven only when the opening action is applied and the spring is reset when the action is closed.
Note: This article takes the DA/SR series pneumatic actuators as an example to illustrate the selection of actuators. The purpose of this reference is to help customers select actuators correctly. Before installing pneumatic/electric actuators into valves, the following factors must be considered. * The operating torque of the valve plus the manufacturer's recommended safety factor / depending on operating conditions. * The air supply pressure or power supply voltage of the actuator. * Actuator type double action or single action (spring return) and output torque at a certain air supply or output torque at rated voltage. * The steering of the actuator and the failure mode (failure or fault clearance) It is very important to select an actuator correctly. If the actuator is too large, the stem may be overstressed. On the contrary, if the actuator is too small, the side cannot generate enough torque to fully operate the valve. In general, we believe that the torque required to operate the valve comes from the friction between the metal parts of the valve (eg core, disc) and the seal (valve seat). Depending on the valve usage, operating temperature, operating frequency, piping and differential pressure, and flowing media (lubrication, drying, mud), many factors affect the operating moment. The structure of the ball valve is basically based on a polished core (including channels). The two valve seats (upstream and downstream), the rotation of the center of the ball intercepts or flows through the core, and the pressure difference between upstream and downstream causes the core to abut against the downstream seat (floating ball structure). In this case, the torque to operate the valve is determined by the friction between the ball and the seat, stem and packing. As shown in FIG. 1 , the maximum torque occurs when the pressure difference occurs and the ball rotates in the open position in the closed position. The structural principle of the butterfly valve is basically based on the butterfly plate fixed on the axis. In the closed position, the butterfly plate and the valve seat are completely sealed. When the disc is rotated (around the valve stem) and parallel to the flow of the fluid, the valve is in the fully open position. On the other hand, when the butterfly plate is perpendicular to the flow of the fluid, the valve is in the closed position. The moment of operating the butterfly valve is determined by the friction between the butterfly plate and the valve seat, the stem and the packing. At the same time, the force of the differential pressure acting on the butterfly plate also influences the operating torque, such as the maximum moment of the valve when it is closed, and the tiny rotation. The torque will significantly reduce the structure of the plug valve. The principle is basically based on a plug that is sealed in a tapered plug body. There is a passage in one direction of the stopper. The valve is opened and closed as the plug is screwed into the valve seat. The operating torque is generally not affected by the pressure of the fluid but is determined by the friction between the valve seat and the plug during opening and closing. When the valve is closed, the torque is maximum. Due to the influence of pressure, the torque is always maintained during the rest of the operation. The working principle of the German BAR pneumatic actuators. Other related editors Double-acting actuators The selection of double-acting actuators takes the DA series pneumatic actuators as an example. The output torque of the gear-bar actuator is obtained by multiplying the piston pressure (source pressure) by the pitch circle radius (arm), and the friction resistance is small and efficient. The output torque is linear when rotated clockwise and counterclockwise. Under normal operating conditions, the recommended safety factor for double-acting actuators is 25-50%
Single-acting actuators The selection of single-acting actuators uses SR-series pneumatic actuators as an example. In spring-return applications, the output torque is obtained in two different operating processes. According to the position of the stroke, each operation produces two Different torque values. The output torque of the spring return actuator is multiplied by force (air pressure or spring force) on the arm. The first condition is that the output torque is obtained by the air pressure entering the compression spring of the middle chamber. The “air stroke output torque†is In this case, the pressure of the air source forces the piston to move from 0 to 90 degrees. Since the spring compression produces a reaction force, the moment gradually decreases from the maximum value at the starting point to the second condition: the output torque is the spring recovery when the middle chamber is out of breath. The force acting on the piston is known as the "spring travel output torque". In this case, due to the elongation of the spring, the output torque gradually decreases from 90 degrees to 0 degrees as described above, the single-acting actuator is based on two It is designed on the basis of a balance moment generated under various conditions. As shown in Figure 11. In each case, it is possible to obtain an unbalanced moment by changing the relationship between the number of springs on each side and the pressure of the air supply (eg 2 springs per side and 5.5 bar source or vice versa). Two conditions can be achieved in spring return applications : Loss of breath or loss of breath. The recommended safety factor for spring-return actuators is 25-50% under normal operating conditions
Selection example of spring return actuator (see also technical data sheet):
Spring shut off (discharge)
* Ball valve torque = 80NM
* Safety factor (25%) = 80NM + 25% = 100NM
*Air pressure = 0.6MPa
The SY-SR actuator chosen is SR125-05 because it produces the following values:
*Spring travel 0o=119.2NM
*Spring travel 90o=216.2NM
*Air stroke 0o=228.7NM
*Air stroke 90o=118.8NM
Comparing with electric actuators In terms of technical performance, the advantages of pneumatic actuators mainly include the following four aspects:
(1) Large load, can adapt to high torque output applications.
(2) rapid action and quick response.
(3) The work environment has good adaptability, especially in the flammable, explosive, dusty, strong magnetic, radiation and vibration and other harsh working environments, superior to hydraulic, electronic and electrical control.
(4) The motor is easily damaged when the stroke is blocked or the valve stem is trapped.
The advantages of electric actuators include:
(1) Compact and compact. Compared to pneumatic actuators, electric actuators are relatively simple in structure. A basic electronic system includes actuators, three-position DPDT switches, fuses, and some wires that are easy to assemble.
(2) The driving source of the electric actuator is very flexible. Generally, the on-board power supply can meet the needs, and the pneumatic actuator needs the air source and the compression drive device.
(3) The electric actuator has no danger of “leakage†and high reliability, while the compressibility of the air makes the stability of the pneumatic actuator somewhat poorer.
(4) It is not necessary to install and maintain various pneumatic lines.
(5) The load can be maintained without power, and pneumatic actuators require continuous pressure supply.
(6) Electric actuators are quieter because no additional pressure device is required. Normally, if the pneumatic actuator is under heavy load, install it.
(7) In the pneumatic device, it is usually required to convert the electric signal into a gas signal, and then convert it into an electric signal. The transmission speed is slow, and it is not suitable for a complex circuit with an excessive number of 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 achieve rapid linear motion, simple structure, easy maintenance, and can be used in a variety of harsh working environments, such as explosion-proof requirements, more dust or wet conditions. However, an electric drive with a servo motor has advantages in the case where the force increases rapidly and precise positioning is required. For applications that require precise, synchronized operation, adjustable and defined positioning programming, electric actuators are the best choice. An electric drive system consisting of a servo or stepper motor with a closed-loop positioning controller can compensate for the lack of a pneumatic system. Department.
In the modern control, various systems are becoming more and more complex and more sophisticated, and it is not a certain driving control technology that can satisfy various control functions of the system. Electric actuators are mainly used in applications where precise control is required. Flexibility requirements in automation equipment are constantly increasing. The same equipment is often required to meet the processing requirements for workpieces of different sizes. Actuators need to perform multi-point positioning control and actuators must be The precise control or synchronous tracking of the operating speed and torque, which cannot be achieved using conventional pneumatic controls, can be very easily achieved with electric actuators. This shows that pneumatic actuators are more suitable for simple motion control, while electric actuators are mostly used for precision motion control applications.
How German BAR Pneumatic Actuator Works
German BAR is a pioneer in the field of self-controlled valves:
In 1981, BAR took the lead in proposing the principle of using rack and pinion, using dual pistons and safety springs to drive the shaft of the actuator. This idea was followed by the world's major manufacturers and was eventually adopted worldwide.
Pneumatic Actuators Pneumatic actuators are actuators that use air pressure to actuate the opening and closing or adjustment of valves. They are also called pneumatic actuators or pneumatic devices, but are generally known as pneumatic heads.
Pneumatic actuator actuator and adjustment mechanism is a unified whole, and its implementing agencies are film, piston, fork-type and rack and pinion 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. The fork type pneumatic actuator has the characteristics of large torque, small space, and the torque curve more consistent with the torque curve of the valve, but is not very beautiful; it is often used on valves with large torque. Rack and pinion type pneumatic actuators have the advantages of simple structure, stable and reliable operation, and safety and explosion proof. They are widely used in power plants, chemical industry, oil refining and other high-security production processes.
Chinese name pneumatic actuator foreign name Pneumaticactuators
Working principle When the compressed air enters the pneumatic actuator from the A nozzle, the gas pushes the double piston to the two ends (cylinder head end) and moves linearly. The rack on the piston drives the gear on the rotary shaft to rotate 90 degrees counterclockwise, the valve is Was opened. At this point, the gas at both ends of the pneumatic actuator valve discharges with the B nozzle. Conversely, when the compressed air enters both ends of the pneumatic actuator from the B officer's nozzle, the gas pushes the double plugs toward the middle of a straight line. The rack on the piston drives the gear on the rotary shaft to rotate 90 degrees clockwise, and the valve is closed. At this moment, the gas in the middle of the pneumatic actuator discharges with the A nozzle. The above is the standard transmission principle. According to the user's requirements, the pneumatic actuator can be equipped with a transmission principle that is the opposite of the standard type. That is, the selective axis rotates clockwise to open the valve and counterclockwise to close the valve. Single-acting (spring return type) pneumatic actuator A nozzle for the inlet, B nozzle for the exhaust hole (B nozzle should be installed muffler). The inlet of the A nozzle is to open the valve. When the air is cut off, the valve is closed by spring force.
The basic structure of the editing internal structure of the pneumatic actuator actuator type and structure are roughly the same, mainly different actuators. Therefore, when the pneumatic actuator is introduced, it is divided into an actuator and a regulating valve. Pneumatic actuator consists of two parts: the actuator and the regulating valve (adjusting mechanism). According to the size of the control signal, a corresponding thrust is generated to push the regulating valve. The regulating valve is the regulating part of the pneumatic actuator. Under the action of the actuator thrust, the regulating valve generates a certain displacement or rotation angle and directly regulates the flow of the fluid.
1. Pneumatic devices are mainly composed of cylinders, pistons, gear shafts, end caps, seals, screws, etc.; complete sets of pneumatic devices should also include opening indication, stroke limit, solenoid valve, positioner, pneumatic components, manual mechanism, signal Feedback and other components.
2. The connection size of pneumatic devices and valves shall comply with the requirements of ISO5211 (bottom), GB/T12222 and GB/T12223.
3, pneumatic device with manual mechanism, in the gas source is interrupted, it should be able to use its manual mechanism to open and close the pneumatic ball valve, facing the hand wheel, the hand wheel or handle should be counterclockwise rotation for the valve to open, clockwise rotation for Valve off.
4. When the end of the piston rod is internally or externally threaded, the spanner wrench should be used for standard wrenches.
5, the piston seal ring should be easy to replace and repair.
6, the pneumatic device with a buffer mechanism, the stroke length of the buffer mechanism can refer to the "Table 1" provisions.
7. Pneumatic devices with adjustable buffer mechanisms shall have mechanisms for external adjustment of the buffering action of the cylinder.
8. The thread size of the air inlet and outlet of the cylinder should meet the requirements of MANURNORM (accessory standard) sypv, GB/T7306.1, GB/T7306.2 and GB/T7307.
The working principle of the German BAR pneumatic actuator performance editor 1, pneumatic device rated output force or torque should be consistent with the provisions of GB/T12222 and GB/T12223 above for the film-type actuator 2, under no-load conditions, the cylinder input according to " The air pressure specified in Table 2 shall be stable and free of jamming and crawling.
3. Under the air pressure of 0.6MPa, the output torque or thrust of the pneumatic device starting and closing in both directions shall not be less than the value indicated by the label of the pneumatic device, and the action shall be flexible, and permanent deformation of each part shall not be allowed. Other abnormalities.
4. When the seal test is conducted with the maximum working pressure, the leakage of air from the respective back pressure side must not exceed (3+0.15D)cm3/min (standard state); leakage from the end cap and output shaft is not allowed. The air volume must not exceed (3+0.15d)cm3/min.
5, strength test with 1.5 times the maximum working pressure test, to maintain the test pressure 3min, the cylinder end cover and static seal parts do not allow leakage and structural deformation.
6, the number of operating life, pneumatic device simulation of pneumatic valve action, in the case of maintaining the output torque or thrust in both directions, the opening and closing of the opening and closing operation should not be less than 50,000 times (start-closed cycle for a).
7. Pneumatic device with buffer mechanism, when the piston moves to the stroke end position, no impact phenomenon is allowed.
Appearance editing 1. End caps, end flanges, and boxes of casting cylinders must be free of scratches, cuts, air holes, and burrs.
2. The paint coating or chemical treatment layer on the outer surface of the pneumatic device should be flat, smooth, uniform in color, free of oil, indentation and other mechanical damage.
Advantage editing 1, receiving a continuous gas signal, output linear displacement (after the power / gas conversion device, you can also receive continuous electrical signal), and some with rocker, you can output the angular displacement.
Pneumatic actuator 2, a positive and negative function.
3, moving speed, but the speed will slow down when the load increases.
4, the output force and operating pressure.
5, high reliability, but the valve can not be maintained after the gas source is interrupted (can be maintained after adding the valve).
6. Inconvenient to realize segmented control and program control.
7, maintenance is simple, good adaptability to the environment.
8, the output power is larger.
9, with explosion-proof function.
Compact double piston gear, rack-type structure, precise meshing, high efficiency, constant output torque.
Aluminum cylinders, pistons and end caps are lightest in weight compared to actuators of the same size.
The cylinder body is an extruded aluminum alloy and hard anodized. The inner surface has a hard texture and high strength and hardness. The use of low-friction materials made of sliding bearings, to avoid direct contact between the metal, low friction coefficient, flexible rotation, long service life.
Pneumatic actuator and valve installation and connection dimensions are designed according to the international standards ISO5211, DIN3337 and VDI/VDE3845 and can be interchanged with common pneumatic actuators.
The gas source hole meets the NAMUR standard.
Pneumatic actuator bottom shaft assembly holes (according to ISO5211 standard) are double quadrilateral, easy to install with linear valve or 45° corner of the valve with square bar.
The top and top holes in the output shaft meet the NAMUR standard.
The adjusting screws at both ends can adjust the opening angle of the valve.
The same specifications are double acting, single acting (spring return).
According to the valve needs to choose the direction, clockwise or counterclockwise rotation.
According to user needs to install the solenoid valve, positioner (degree of opening instructions), reply, all kinds of limit switches and manual operation device.
Disadvantages The low precision of editing and control, dual-acting pneumatic actuator, can not return to the preset position after the air source is cut off. Single Acting Pneumatic Actuator, After Air Supply Can Rely On The Spring Back To Presume Category Selection Editor According to its energy form, it can be divided into three categories: 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 categorized into single-acting and double-acting types: The actuator's switching action is driven by the air source and is called DOUBLE ACTING (double acting). The SPRINGRETURN (single acting) switch action is air driven only when the opening action is applied and the spring is reset when the action is closed.
Note: This article takes the DA/SR series pneumatic actuators as an example to illustrate the selection of actuators. The purpose of this reference is to help customers select actuators correctly. Before installing pneumatic/electric actuators into valves, the following factors must be considered. * The operating torque of the valve plus the manufacturer's recommended safety factor / depending on operating conditions. * The air supply pressure or power supply voltage of the actuator. * Actuator type double action or single action (spring return) and output torque at a certain air supply or output torque at rated voltage. * The steering of the actuator and the failure mode (failure or fault clearance) It is very important to select an actuator correctly. If the actuator is too large, the stem may be overstressed. On the contrary, if the actuator is too small, the side cannot generate enough torque to fully operate the valve. In general, we believe that the torque required to operate the valve comes from the friction between the metal parts of the valve (eg core, disc) and the seal (valve seat). Depending on the valve usage, operating temperature, operating frequency, piping and differential pressure, and flowing media (lubrication, drying, mud), many factors affect the operating moment. The structure of the ball valve is basically based on a polished core (including channels). The two valve seats (upstream and downstream), the rotation of the center of the ball intercepts or flows through the core, and the pressure difference between upstream and downstream causes the core to abut against the downstream seat (floating ball structure). In this case, the torque to operate the valve is determined by the friction between the ball and the seat, stem and packing. As shown in FIG. 1 , the maximum torque occurs when the pressure difference occurs and the ball rotates in the open position in the closed position. The structural principle of the butterfly valve is basically based on the butterfly plate fixed on the axis. In the closed position, the butterfly plate and the valve seat are completely sealed. When the disc is rotated (around the valve stem) and parallel to the flow of the fluid, the valve is in the fully open position. On the other hand, when the butterfly plate is perpendicular to the flow of the fluid, the valve is in the closed position. The moment of operating the butterfly valve is determined by the friction between the butterfly plate and the valve seat, the stem and the packing. At the same time, the force of the differential pressure acting on the butterfly plate also influences the operating torque, such as the maximum moment of the valve when it is closed, and the tiny rotation. The torque will significantly reduce the structure of the plug valve. The principle is basically based on a plug that is sealed in a tapered plug body. There is a passage in one direction of the stopper. The valve is opened and closed as the plug is screwed into the valve seat. The operating torque is generally not affected by the pressure of the fluid but is determined by the friction between the valve seat and the plug during opening and closing. When the valve is closed, the torque is maximum. Due to the influence of pressure, the torque is always maintained during the rest of the operation. The working principle of the German BAR pneumatic actuators. Other related editors Double-acting actuators The selection of double-acting actuators takes the DA series pneumatic actuators as an example. The output torque of the gear-bar actuator is obtained by multiplying the piston pressure (source pressure) by the pitch circle radius (arm), and the friction resistance is small and efficient. The output torque is linear when rotated clockwise and counterclockwise. Under normal operating conditions, the recommended safety factor for double-acting actuators is 25-50%
Single-acting actuators The selection of single-acting actuators uses SR-series pneumatic actuators as an example. In spring-return applications, the output torque is obtained in two different operating processes. According to the position of the stroke, each operation produces two Different torque values. The output torque of the spring return actuator is multiplied by force (air pressure or spring force) on the arm. The first condition is that the output torque is obtained by the air pressure entering the compression spring of the middle chamber. The “air stroke output torque†is In this case, the pressure of the air source forces the piston to move from 0 to 90 degrees. Since the spring compression produces a reaction force, the moment gradually decreases from the maximum value at the starting point to the second condition: the output torque is the spring recovery when the middle chamber is out of breath. The force acting on the piston is known as the "spring travel output torque". In this case, due to the elongation of the spring, the output torque gradually decreases from 90 degrees to 0 degrees as described above, the single-acting actuator is based on two It is designed on the basis of a balance moment generated under various conditions. As shown in Figure 11. In each case, it is possible to obtain an unbalanced moment by changing the relationship between the number of springs on each side and the pressure of the air supply (eg 2 springs per side and 5.5 bar source or vice versa). Two conditions can be achieved in spring return applications : Loss of breath or loss of breath. The recommended safety factor for spring-return actuators is 25-50% under normal operating conditions
Selection example of spring return actuator (see also technical data sheet):
Spring shut off (discharge)
* Ball valve torque = 80NM
* Safety factor (25%) = 80NM + 25% = 100NM
*Air pressure = 0.6MPa
The SY-SR actuator chosen is SR125-05 because it produces the following values:
*Spring travel 0o=119.2NM
*Spring travel 90o=216.2NM
*Air stroke 0o=228.7NM
*Air stroke 90o=118.8NM
Comparing with electric actuators In terms of technical performance, the advantages of pneumatic actuators mainly include the following four aspects:
(1) Large load, can adapt to high torque output applications.
(2) rapid action and quick response.
(3) The work environment has good adaptability, especially in the flammable, explosive, dusty, strong magnetic, radiation and vibration and other harsh working environments, superior to hydraulic, electronic and electrical control.
(4) The motor is easily damaged when the stroke is blocked or the valve stem is trapped.
The advantages of electric actuators include:
(1) Compact and compact. Compared to pneumatic actuators, electric actuators are relatively simple in structure. A basic electronic system includes actuators, three-position DPDT switches, fuses, and some wires that are easy to assemble.
(2) The driving source of the electric actuator is very flexible. Generally, the on-board power supply can meet the needs, and the pneumatic actuator needs the air source and the compression drive device.
(3) The electric actuator has no danger of “leakage†and high reliability, while the compressibility of the air makes the stability of the pneumatic actuator somewhat poorer.
(4) It is not necessary to install and maintain various pneumatic lines.
(5) The load can be maintained without power, and pneumatic actuators require continuous pressure supply.
(6) Electric actuators are quieter because no additional pressure device is required. Normally, if the pneumatic actuator is under heavy load, install it.
(7) In the pneumatic device, it is usually required to convert the electric signal into a gas signal, and then convert it into an electric signal. The transmission speed is slow, and it is not suitable for a complex circuit with an excessive number of 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 achieve rapid linear motion, simple structure, easy maintenance, and can be used in a variety of harsh working environments, such as explosion-proof requirements, more dust or wet conditions. However, an electric drive with a servo motor has advantages in the case where the force increases rapidly and precise positioning is required. For applications that require precise, synchronized operation, adjustable and defined positioning programming, electric actuators are the best choice. An electric drive system consisting of a servo or stepper motor with a closed-loop positioning controller can compensate for the lack of a pneumatic system. Department.
In the modern control, various systems are becoming more and more complex and more sophisticated, and it is not a certain driving control technology that can satisfy various control functions of the system. Electric actuators are mainly used in applications where precise control is required. Flexibility requirements in automation equipment are constantly increasing. The same equipment is often required to meet the processing requirements for workpieces of different sizes. Actuators need to perform multi-point positioning control and actuators must be The precise control or synchronous tracking of the operating speed and torque, which cannot be achieved using conventional pneumatic controls, can be very easily achieved with electric actuators. This shows that pneumatic actuators are more suitable for simple motion control, while electric actuators are mostly used for precision motion control applications.
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