Detailed Analysis of Valve Actuation Torque Characteristics
On this page
Valve actuation torque is a critical factor in valve design, selection, and operation. The torque characteristics vary among different types of valves, directly influencing their performance under different operating conditions and maintenance requirements. This article provides a detailed analysis of the actuation torque characteristics of gate valves, globe valves, butterfly valves, and ball valves, and explores their significance and management strategies in practical applications.
The actuation torque characteristics of gate valves directly impact their operational performance. Below, we examine the variation patterns of gate valve actuation torque, the comparison between rigid and flexible gate plates, the influence of sealing methods, and the effects of temperature changes, to understand how these factors affect gate valve operation.
Gate valve actuation torque exhibits specific variation patterns during operation. When the valve opening is greater than 10%, the axial force, or actuation torque, changes relatively little. However, when the valve opening is less than 10%, the pressure differential across the valve increases due to throttling of the fluid, which directly affects the gate plate, increasing the axial force required to drive the gate plate and significantly raising the actuation torque in this range.
The performance of rigid and flexible gate plates in the actuation torque curve of gate valves differs. Flexible gate plate valves typically require more actuation torque near the closed position compared to rigid gate plates. This difference is primarily due to the additional sealing force required to ensure reliable sealing with a flexible gate plate.
The sealing method of a gate valve has a significant impact on its actuation torque characteristics. In active sealing gate valves (e.g., wedge gate valves), the fully closed position is usually determined by the gate plate's position, which is difficult to monitor in operation. Therefore, the valve is generally closed to its stop point as the fully closed position. For restrained sealing gate valves, the fully closed position is determined by the torque applied to the valve stem nut, which continues to exert sealing force after the valve is closed, ensuring tight sealing.
It is important to note that temperature changes of the medium or environment after the valve is closed can lead to thermal expansion of valve components, increasing the pressure between the gate plate and the seat. This increased pressure can make it difficult to reopen the valve, significantly increasing the required actuation torque. Therefore, it is crucial to consider the impact of temperature changes on valve actuation torque and take appropriate measures to ensure smooth valve operation.
The actuation torque characteristics of globe valves are important parameters in valve operation, involving torque changes during valve opening and closing, as well as the determination of the fully open position. The following details explore these characteristics to understand their performance in globe valve operation.
The actuation torque characteristics of globe valves are closely related to the direction of the medium flow and the movement of the valve disc. When the medium enters the valve cavity from below, the pressure differential formed as the valve disc descends will hinder further descent. This hindrance increases rapidly with the valve disc's descent, reaching a maximum pressure differential as the valve approaches the fully closed position, causing a sharp increase in actuation torque due to the restraint sealing force.
During valve opening, the thrust created by the medium's pressure and pressure differential assists in opening the valve, so the opening torque characteristic curve is usually below the closing torque curve. Particularly at the moment of opening, the torque required to overcome larger static friction may exceed that required for closing.
The fully open position of a globe valve is generally determined by the stroke of the valve disc. When the disc reaches the height corresponding to the nominal diameter of the valve, the flow rate reaches its maximum, and the valve is considered fully open. The closing torque characteristics are similar to those of restrained sealing gate valves, so the closed position is typically determined by changes in actuation torque.
Butterfly valves exhibit distinct torque characteristics during operation, which are essential for efficient valve operation. Below is a specific analysis of the torque characteristics of butterfly valves.
The actuation torque characteristic curve of butterfly valves typically shows a high center and low ends. This is due to the fluid being obstructed by the butterfly plate and forming a swirling flow that creates a hydrodynamic torque in the closing direction when the butterfly plate is in the middle position. As the plate opens or closes further, the impact of the swirling flow diminishes, reducing the obstruction and forming the described characteristic curve.
The maximum actuation torque for unsealed butterfly valves occurs at the mid-position, while for sealed butterfly valves, it is at the closed position. The latter experiences a significant increase in actuation torque due to the additional sealing torque.
Butterfly valve stems only rotate, and the butterfly plate and stem do not have inherent self-locking capability. Therefore, to ensure the plate stays in the designated position, a self-locking reducer device, such as a worm gear reducer, is typically added to the valve stem. This addition improves angular displacement accuracy and reduces actuation torque, bringing the butterfly valve's performance closer to other types of valves and facilitating compatibility with electric actuators.
Ball valves exhibit some similarities in torque characteristics to butterfly valves. The following is a brief analysis of ball valve actuation torque characteristics.
The actuation torque characteristic curve of ball valves is similar to that of butterfly valves, primarily influenced by the swirling flow caused by changes in fluid direction inside the ball. As the valve opens or closes, the impact of swirling flow decreases, and the actuation torque changes accordingly.
The actuation torque characteristics of ball valves are also closely related to their rotation angle. Ball valves rotate 90 degrees from fully open to fully closed, typically requiring mechanical stops to ensure the valve stops at the correct position. The opening and closing positions of the ball valve are determined by the stem's rotation angle, so ball valves are positioned by stroke.
Understanding the actuation torque characteristics of different types of valves is crucial for valve selection, design, and maintenance. In practical applications, the torque characteristics under different conditions can significantly affect the ease of operation and system reliability. Therefore, during the design and selection process, it is essential to fully consider the torque characteristics of the valve and appropriately configure the actuation torque to meet process requirements and ensure stable system operation.
Gate Valve Actuation Torque Characteristics
The actuation torque characteristics of gate valves directly impact their operational performance. Below, we examine the variation patterns of gate valve actuation torque, the comparison between rigid and flexible gate plates, the influence of sealing methods, and the effects of temperature changes, to understand how these factors affect gate valve operation.
1. Torque Variation Patterns
Gate valve actuation torque exhibits specific variation patterns during operation. When the valve opening is greater than 10%, the axial force, or actuation torque, changes relatively little. However, when the valve opening is less than 10%, the pressure differential across the valve increases due to throttling of the fluid, which directly affects the gate plate, increasing the axial force required to drive the gate plate and significantly raising the actuation torque in this range.
2. Comparison Between Rigid and Flexible Gate Plates
The performance of rigid and flexible gate plates in the actuation torque curve of gate valves differs. Flexible gate plate valves typically require more actuation torque near the closed position compared to rigid gate plates. This difference is primarily due to the additional sealing force required to ensure reliable sealing with a flexible gate plate.
3. Impact of Sealing Methods
The sealing method of a gate valve has a significant impact on its actuation torque characteristics. In active sealing gate valves (e.g., wedge gate valves), the fully closed position is usually determined by the gate plate's position, which is difficult to monitor in operation. Therefore, the valve is generally closed to its stop point as the fully closed position. For restrained sealing gate valves, the fully closed position is determined by the torque applied to the valve stem nut, which continues to exert sealing force after the valve is closed, ensuring tight sealing.
4. Effects of Temperature Changes
It is important to note that temperature changes of the medium or environment after the valve is closed can lead to thermal expansion of valve components, increasing the pressure between the gate plate and the seat. This increased pressure can make it difficult to reopen the valve, significantly increasing the required actuation torque. Therefore, it is crucial to consider the impact of temperature changes on valve actuation torque and take appropriate measures to ensure smooth valve operation.
Globe Valve Actuation Torque Characteristics
The actuation torque characteristics of globe valves are important parameters in valve operation, involving torque changes during valve opening and closing, as well as the determination of the fully open position. The following details explore these characteristics to understand their performance in globe valve operation.
1. Closing Torque Characteristics
The actuation torque characteristics of globe valves are closely related to the direction of the medium flow and the movement of the valve disc. When the medium enters the valve cavity from below, the pressure differential formed as the valve disc descends will hinder further descent. This hindrance increases rapidly with the valve disc's descent, reaching a maximum pressure differential as the valve approaches the fully closed position, causing a sharp increase in actuation torque due to the restraint sealing force.
2. Opening Torque Characteristics
During valve opening, the thrust created by the medium's pressure and pressure differential assists in opening the valve, so the opening torque characteristic curve is usually below the closing torque curve. Particularly at the moment of opening, the torque required to overcome larger static friction may exceed that required for closing.
3. Determination of Fully Open Position
The fully open position of a globe valve is generally determined by the stroke of the valve disc. When the disc reaches the height corresponding to the nominal diameter of the valve, the flow rate reaches its maximum, and the valve is considered fully open. The closing torque characteristics are similar to those of restrained sealing gate valves, so the closed position is typically determined by changes in actuation torque.
Butterfly Valve Actuation Torque Characteristics
Butterfly valves exhibit distinct torque characteristics during operation, which are essential for efficient valve operation. Below is a specific analysis of the torque characteristics of butterfly valves.
1. Torque Characteristic Curve
The actuation torque characteristic curve of butterfly valves typically shows a high center and low ends. This is due to the fluid being obstructed by the butterfly plate and forming a swirling flow that creates a hydrodynamic torque in the closing direction when the butterfly plate is in the middle position. As the plate opens or closes further, the impact of the swirling flow diminishes, reducing the obstruction and forming the described characteristic curve.
2. Comparison Between Sealed and Unsealed Butterfly Valves
The maximum actuation torque for unsealed butterfly valves occurs at the mid-position, while for sealed butterfly valves, it is at the closed position. The latter experiences a significant increase in actuation torque due to the additional sealing torque.
3. Self-Locking Capability and Positioning Devices
Butterfly valve stems only rotate, and the butterfly plate and stem do not have inherent self-locking capability. Therefore, to ensure the plate stays in the designated position, a self-locking reducer device, such as a worm gear reducer, is typically added to the valve stem. This addition improves angular displacement accuracy and reduces actuation torque, bringing the butterfly valve's performance closer to other types of valves and facilitating compatibility with electric actuators.
Ball Valve Actuation Torque Characteristics
Ball valves exhibit some similarities in torque characteristics to butterfly valves. The following is a brief analysis of ball valve actuation torque characteristics.
1. Similarity to Butterfly Valves
The actuation torque characteristic curve of ball valves is similar to that of butterfly valves, primarily influenced by the swirling flow caused by changes in fluid direction inside the ball. As the valve opens or closes, the impact of swirling flow decreases, and the actuation torque changes accordingly.
2. Rotation Angle and Limiting Devices
The actuation torque characteristics of ball valves are also closely related to their rotation angle. Ball valves rotate 90 degrees from fully open to fully closed, typically requiring mechanical stops to ensure the valve stops at the correct position. The opening and closing positions of the ball valve are determined by the stem's rotation angle, so ball valves are positioned by stroke.
Understanding the actuation torque characteristics of different types of valves is crucial for valve selection, design, and maintenance. In practical applications, the torque characteristics under different conditions can significantly affect the ease of operation and system reliability. Therefore, during the design and selection process, it is essential to fully consider the torque characteristics of the valve and appropriately configure the actuation torque to meet process requirements and ensure stable system operation.
