Valve torque and actuator

Valve torque refers to the valve the required twisting force when the valve is opened or closed, which is one of the main parameters for choosing the valve driving actuator. Close the valve between the opening and closing parts of the seat sealing surface to form a sealed pressure, but also to overcome the stem and packing, stem and nut thread, stem end support and other friction parts of the friction force, where the need for a certain opening force, its maximum is in the final moment of closure or the initial moment of opening. The opening torque of the manual valve should not exceed 360N•m, if exceeded, appropriate driving actuators such as electric, pneumatic and hydraulic should be considered. Valves should be designed and manufactured to reduce the opening/closing force and torque.

The opening torque is also known as the operating torque and can be obtained by calculation or measurement, or by actual measurement by the tools like a torque wrench. Electric and pneumatic actuators are available for 1.5 times the valve torque. When the valve opening torque is too large, the gear or worm gear transmission can be used for driving. The torque of different types of valves is different. There are three types of friction to be considered when calculating the torque of ball valve: ball and seat friction torque; Friction torque of packing on the stem; The friction torque of the bearing on the stem, how to calculate the torque of the ball valve? The total stem torque of the ball valve.

M=M1+M2+M3

M1: Friction torque between the ball and sealing surface of valve seat.

M2: Friction torque between packing and stem due to medium pressure.

M3: Friction torque on top of the stem.

In addition, comprehensive consideration of medium, material and other parts of the friction factor when calculating valve torque. Because there are so many types of disc, seat, and packing, they all have different friction, contact surfaces, compression, and so on. The calculated valve torque differs from the actual measured value and cannot be used as a guide. The exact value needs to be corrected in combination with the valve manufacturer’s test results.