Understanding the Operation Characteristics of Globe Valves

 
Globe valves, also known as gate valves, are crucial components in fluid control systems, designed to regulate the flow of media by opening and closing passages. Their distinctive feature lies in their forced sealing mechanism, which necessitates the application of pressure to ensure the sealing surfaces remain leak-proof when the valve is shut.



In the operation of globe valves, several key factors come into play. Firstly, there's the consideration of operating force. As the medium enters the valve from beneath the valve disc, the force required to operate must overcome the friction between the valve stem and packing, as well as the thrust generated by the medium's pressure. Given that closing the valve requires greater force compared to opening it, the diameter of the valve stem must be adequately sized to prevent bending at its apex.
 
Moreover, the torque characteristic of globe valves is a significant aspect to be understood. Typically, the torque curve of a globe valve exhibits a pattern of high values in the middle and lower values at both ends. This phenomenon arises from the obstruction of fluid flow by the disc when the valve is in the middle position, creating vortices around the disc and exerting a hydraulic torque that forces closure. As the disc opens or closes, the impact of these vortices diminishes until they dissipate entirely, resulting in reduced resistance and torque at the valve's extremes.
 
The type of globe valve also influences its torque characteristics. Non-sealing globe valves typically experience maximum torque at the middle position, whereas sealing globe valves exhibit peak torque when the valve is fully closed. This disparity is attributable to the additional forced sealing torque required by sealing globe valves to maintain integrity.
 
Furthermore, to ensure precise positioning of the valve, it's common practice to install a self-locking reducer on the valve stem. By incorporating a worm gear reducer, the number of revolutions required to achieve angular displacement can be increased while simultaneously reducing operating torque. This enables the performance of globe valves to align closely with that of other valve types, facilitating the integration of electric actuators.
 
In conclusion, for globe valves with forced sealing requirements, the closing position should be determined based on the specified increase in operating torque. Therefore, when selecting and designing globe valves, a comprehensive understanding of their type, torque characteristics, and sealing requirements is essential to ensure their reliability and stability in real-world applications.