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Components of Valve Opening Torque

Release time:

Sep 30,2024

The opening torque of the valve is mainly composed of four parts: the sealing friction torque of the valve seat, the friction torque of the valve stem and packing, the friction torque of the valve stem and bearing, and the fluid action torque

   The opening torque of the valve is mainly composed of four parts: the sealing friction torque of the valve seat, the friction torque of the valve stem and packing, the friction torque of the valve stem and bearing, and the fluid action torque：

    1. Sealing friction torque: The sealing structure of a valve usually consists of a contact seal between the seat and the spool. When the valve is closed, there is a certain pressure between the sealing surfaces to ensure that the fluid will not leak. When the valve is opened, the friction between the sealing surfaces needs to be overcome, and the torque generated by this part of the friction is the sealing friction torque.

   The size of the sealing friction torque is related to the material of the sealing surface, processing accuracy, sealing pressure and the use of the valve time and other factors. Generally speaking, the higher the hardness of the sealing surface material, the better the machining precision and the higher the sealing pressure, the higher the sealing friction torque. And with the growth of the valve's use time, the sealing surface may be worn, which leads to an increase in the sealing friction torque.

    2. Stem and packing friction moment: In order to prevent fluid leakage from the stem, valves are usually set around the stem packing. There is a certain amount of friction between the packing and the valve stem, when opening the valve, you need to overcome this part of the friction, the resulting torque is the stem and packing friction torque.

    The size of the friction torque between the valve stem and the packing is related to the material of the packing, the degree of compression, the surface roughness of the valve stem and the operating frequency of the valve. The larger the coefficient of friction of the packing material, the higher the degree of compression, and the rougher the surface of the valve stem, the larger the friction torque between the valve stem and the packing. Frequent operation of the valve will cause the packing to wear out gradually, thus leading to an increase in the friction torque.

    3. Stem and bearing friction torque: The stem of the valve is usually supported on the valve body by the bearing to ensure smooth rotation of the stem. When opening the valve, it is necessary to overcome the friction between the stem and the bearing, and the torque generated by this part of the friction is the stem and bearing friction torque.

   The size of the friction torque between the valve stem and the bearing is related to the type of bearing, the lubrication, the diameter of the stem and the operating speed of the valve. The friction moment of rolling bearings is usually smaller than that of plain bearings; good lubrication can significantly reduce the friction moment; the larger the diameter of the valve stem, the friction moment will also increase accordingly. The larger the stem diameter, the greater the frictional torque will be. Too fast an operating speed may cause the bearing to heat up, thus increasing the frictional torque.

    4. Fluid action torque: When the fluid passes through the valve, it will produce force on the spool of the valve, including the pressure difference generated by the thrust and the impact force generated by the fluid flow. In the opening of the valve, the need to overcome these fluid force, the resulting torque that is the fluid action torque.

    The size of the fluid action moment is related to the fluid pressure, flow rate, flow rate, the structure of the valve form and the shape of the spool and other factors. The greater the fluid pressure, the greater the flow rate, the faster the flow rate, the greater the fluid torque. Different structural forms of valves and different shapes of the spool on the fluid force is also different.

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