What Is a Pneumatic Rotary Actuator?

GT pneumatic actuator is the most commonly used type of pneumatic actuator. In the pneumatic actuator market, pneumatic actuators should occupy more than 80%. The characteristics of pneumatic actuators are cheap, small in size, light in weight, large in market ownership, and action flexible. As long as the air source can open and close the valve, it is safe and reliable.

GT pneumatic actuator

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GT pneumatic actuator is the most commonly used type of pneumatic actuator. In the pneumatic actuator market, the pneumatic actuator should occupy more than 80%.

GT's pneumatic actuator's ground holding mechanism and adjustment mechanism are a unified whole.

GT pneumatic actuator is mainly used to cut off or connect the medium in the pipeline, and it can also be used to regulate and control the fluid. Compared with other valves, it has the following advantages.

7 advantages of GT pneumatic actuator

1. Small fluid resistance. Ball valve is the smallest fluid resistance among all valves. Even a reduced diameter ball valve has a relatively small fluid resistance.

2. The thrust bearing reduces the friction torque of the valve stem, which can make the valve stem operate in a balanced and flexible way for a long time.

3. The valve seat has good sealing performance. The sealing ring made of polytetrafluoroethylene and other materials has a structure that is easy to seal, and the valve sealing capacity of the ball valve increases with the increase of the medium pressure.

4. The valve stem has a reliable seal. Because the valve stem only performs a rotary motion and does not perform a lifting movement, the packing seal of the valve stem is not easy to break, and the sealing capacity increases with the increase of the pressure of the medium.

5. Because materials such as polytetrafluoroethylene have good self-lubrication, the friction loss with the ball is small, and the service life of the ball valve is large.

6. Bottom-type stem and convex head of the stem prevent the stem from spraying out. If the valve stem seal is damaged due to fire, metal contact can be formed between the convex step and the valve body to ensure the stem seal.

7, anti-static function: a spring is installed between the ball, valve stem, and valve body, which can discharge the static electricity generated during the switching process.

GT pneumatic actuator is a fully sealed, modular, and provincial product. It introduced foreign technology in the early 1990s. It is the earliest domestic research and development company. It sells well in China and other European and Asian countries.

1. GT pneumatic actuator is connected to the valve in accordance with ISO5211 standard, and can be directly connected to the valve. It can also be connected to any valve through transition brackets and joints.

2. The coaxiality of GT pneumatic actuator and rotary shaft and valve shaft must be guaranteed during installation.

3. The pipe joint and the inside of the pipe should be cleaned without excess, dust and oil.

4. GT pneumatic actuators can be connected to solenoid valves, positioners, filters, pressure reducing valves, etc.

Pneumatic actuators have low control accuracy. Double-acting pneumatic actuators cannot return to the preset position after the air source is disconnected. The single-acting pneumatic actuator can return to the preset position by spring after the air source is cut off. The advantage is that the pneumatic actuator is cheap and can meet more than 80% of the working conditions.

The working principle of the double-acting pneumatic actuator is that the air intake of one end of the pneumatic actuator is open and the air intake of one end is closed. According to the customer's needs, the direction can be changed. The working principle of the single-acting GTE pneumatic actuator is: the air inlet valve at one end of the pneumatic actuator is opened, and the valve is closed by spring force when the gas is cut off.

The compact double-piston rack-and-pinion structure of the pneumatic actuator provides precise meshing, high efficiency, and constant output torque.

GT pneumatic actuators can also be divided into two types: single-acting and double-acting: the switching actions of GTD actuators are driven by air sources and are called DOUBLE ACTING (double-acting GTD pneumatic actuators). The switching action of the SPRING RETURN (single acting GTE pneumatic actuator) is only air-driven, and the spring returns when it is closed.

Selection of double acting GTD pneumatic actuator

Take GTD pneumatic actuator as an example to explain the selection of the actuator. The purpose of this reference is to help customers choose the correct actuator. Before installing the pneumatic / electric actuator to the valve, the following factors must be considered.

1. The valve's operating torque plus the manufacturer's recommended safety factor / based on operating conditions.

2. Air source pressure or power supply voltage of the actuator.

3. Type of actuator: double-acting or single-acting (spring return) and output torque under a certain air source or output torque under rated voltage.

4. The steering of the actuator and the failure mode (fault on or fault off) It is very important to choose an actuator correctly. If the actuator is too large, the valve stem may be stressed too much. Conversely, if the actuator is too small, the side cannot generate enough torque to fully operate the valve.

Generally speaking, we believe that the torque required to operate the valve comes from the friction between the valve's metal parts (such as the ball core, the valve disc) and the seal (the valve seat). According to the use of the valve, operating temperature, operating frequency, pipeline and pressure difference, flowing medium (lubrication, drying, mud), many factors affect the operating torque. The structure of the ball valve is basically based on a polished ball core (including the channel) Between the two valve seats (upstream and downstream), the rotation of the ball center intercepts the fluid or flows through the core. The force generated by the pressure difference between the upstream and downstream places the ball core against the downstream valve seat (floating ball structure). . In this case, the torque for operating the valve is determined by the friction between the ball core and the valve seat, the valve stem and the packing. As shown in Figure 1, the maximum torque occurs when the pressure difference occurs and the ball rotates in the open position from the closed position to the butterfly valve. 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 is completely sealed with the valve seat. When the butterfly plate rotates (around the valve stem) and is parallel to the fluid flow direction, the valve is in the fully open position. Conversely, when the disc is perpendicular to the direction of fluid flow, the valve is in the closed position. The torque for operating the butterfly valve is determined by the friction between the butterfly plate and the valve seat, the valve stem and the packing. At the same time, the force of the pressure difference on the butterfly plate also affects the operating torque. The torque will be significantly reduced. The structural principle of the plug valve is basically based on the plug sealed in the conical 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. 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. The valve has the highest torque when closed. Due to the influence of pressure, a high torque is always maintained during the remaining operations.

Selection of single-acting GTE actuator

Taking the GTE series pneumatic actuator as an example, 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), and has low friction resistance and high efficiency. Under normal operating conditions, the recommended safety factor for double acting actuators is 25-50%. Take the GTE 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%.