What are the classifications of pneumatic valve actuators

It is very important to select the actuator correctly. If the actuator is too large, the stem may be stressed too much. Conversely, if the actuator is too small, the torque required to fully operate the valve will not occur. Generally speaking, we believe that the torque required to operate the valve comes from the conflict between the metal parts of the valve (e.g., ball, disc) and the seal (seat). Depending on valve usage, temperature, operating frequency, pipe and pressure differential, fluid medium (smooth, dry, mud), many factors can affect operating torque.

In order to select the actuator correctly, it is necessary to consider the following factors before attaching the pneumatic/electric actuator to the valve.

1. Valve operating torque plus manufacturer's recommended safety factor/according to operating conditions.

2. Air supply pressure or power supply voltage of pneumatic valve actuator.

3. The actuator type is double effect or single effect (spring return), and the output torque is the output torque under certain air source or the output torque under rated voltage.

4. Steering and fault mode of pneumatic actuator (fault open or fault closed).

The principle of ball valve construction is basically based on polishing the center (containing the channel) sandwiched between the two seats (upstream and downstream), the center of ball rotation intercepting or flowing through the center, and the pressure difference between upstream and downstream occurring by the force holding the center with the downstream seat (float structure). In this case, the torque to operate the valve depends on the conflict between the ball and the seat, stem, and packing. Large torques occur when pressure differentials occur and the center rotates in the open direction in the closed orientation.

The structure principle of butterfly valve is basically to fix the disc in the center of the shaft. Disc is fully sealed with seat in closed position. The valve is fully open when the disc rotates (around the stem) and is parallel to the fluid movement. In contrast, the valve is closed when the disc is perpendicular to the movement of the fluid. Butterfly valve torque depends on disc and seat, stem and packing conflict. At the same time, the force exerted by the pressure difference on the disc also affects the operating torque. For example, when the valve is closed, the torque is high, and a slight turn can greatly reduce the torque.

The construction principle of the plug valve is basically based on the cock sealed in the body of the conical cock. There is a channel in one direction of the plug. The valve opens and closes when the plug is screwed into the seat. Operating torque is generally not affected by fluid pressure, but by seat and plug conflicts during opening and closing. High torque when valve is closed. Because of the pressure, high torque has been maintained in other operations.