If the valve actuator is too small, the side cannot generate enough torque to fully operate the valve. In general, we believe that the required valve operating torque comes from the friction between the metal parts of the valve (such as the ball, the disc) and the seal (seat). Depending on the valve application, temperature, operating frequency, piping and differential pressure, flow medium (lubrication, drying, mud), many factors affect the valve operating torque.

Ball valve operating torque

The structural principle of the ball valve is basically based on a polishing core (including the passage) sandwiched between the two seats (upstream and downstream). The rotation of the valve core intercepts or flows the fluid through the center of the ball, upstream and downstream. The force generated by the difference causes the core to abut against the downstream seat (floating ball valve structure). The torque to operate the valve in this case is determined by the friction between the ball and the seat, the stem and the packing. The large value of the moment Z occurs when a pressure difference occurs and the core rotates in the opening direction in the closed position.

Butterfly valve operating torque

The structural principle of the butterfly valve is basically based on the disc fixed to the shaft center. In the closed position, the disc is completely sealed from the valve seat. When the disc rotates (around the valve stem) and is parallel to the flow of the fluid, the valve is in the fully open position. Conversely, when the disc is perpendicular to the flow of the fluid, the valve is in the closed position. The torque of the butterfly valve is determined by the friction between the disc and the valve seat, the stem and the packing, and the force exerted by the differential pressure on the disc also affects the operating torque. When the valve is closed, the moment Z is large, and after a slight rotation, the torque will be significantly reduced.

Plug valve operating torque

The structural principle of the plug valve is basically based on the plug sealed in the tapered plug body. There is a passage in one direction of the plug of the plug valve. The valve is opened and closed as the plug is screwed into the valve seat. The operating torque is usually not affected by the pressure of the fluid but by the friction between the valve seat and the plug during opening and closing. When the plug valve is closed, the moment Z is large. Due to the pressure, the high torque is always maintained during the rest of the operation.