First, pneumatic actuator structure:
Pneumatic actuators are divided into single ACTING and DOUBLE ACTING two types: the switching action of the actuator is driven by the air source, which is called double acting. SPRING RETURN (single action) only the on action is air source driven, and the off action is spring return (AT32 no single action). The actuator and regulating mechanism of the pneumatic actuator are a unified whole, and the actuator has a film type, a piston type and a pinion and rack type. The piston type has a long stroke and is suitable for occasions requiring greater thrust; The film stroke is small, can only directly drive the valve stem. Because the pinion and rack type pneumatic actuator has the advantages of simple structure, large output thrust, stable and reliable action, and safety and explosion-proof, it is widely used in the production process of power plant, chemical industry, oil refining and other high safety requirements.
Second, the principle of pneumatic actuator:
Taking the AT\SR pneumatic actuator series as an example, the purpose of this reference is to help customers correctly select the actuator. Before installing the pneumatic/electric actuator to the valve, the following factors must be considered.
1, the operating torque of the valve plus the safety factor recommended by the manufacturer/according to the operating condition.
2. Air source pressure or power supply voltage of the actuator.
3, the type of actuator double action or single action (spring return) and the output torque under a certain air source or output torque under rated voltage.
4, the steering of the actuator and the fault mode (fault on or fault off) is very important to correctly select an actuator, such as the actuator is too large, the valve stem may be too stressed. On the contrary, 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 metal parts of the valve (such as the ball core, valve disc) and the seal (seat). According to the valve use occasion, use temperature, operating frequency, pipe and pressure difference, flow medium (lubrication, drying, mud), many factors affect the operating torque.
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