An Analysis of Defects in Wedge Gate Valves
Wedge gate valves, as a common type of gate valve, find widespread application in industrial production. However, despite their advantages such as forced sealing, wedge gate valves also exhibit several defects and issues that may affect their performance, safety, and lifespan. Below is an analysis and summary of the main defects associated with wedge gate valves.
1. High Operating Torque
One prominent defect of wedge gate valves is the significant operating torque required during opening and closing. Particularly during the initial opening moment, substantial static friction exists, leading to a high operating torque. To ensure proper operation, it often necessitates the installation of high-power electric actuators, thereby inadvertently increasing manufacturing and operational costs. Moreover, excessive closing torque can easily damage sealing surfaces or valve components, consequently reducing the valve's lifespan.
2. Wedging at High Temperatures
A critical issue with wedge gate valves occurs at elevated temperatures, known as "wedging." When material strength decreases and sealing surface hardness diminishes, the sealing pair enters a state of adhesive stickiness. Improper adjustment of closing torque under such conditions, combined with thermal expansion of the valve stem, can result in a sharp increase in sealing surface pressure, leading to wedging. Forced opening actions at this stage can cause sealing surface abrasion, leading to leakage or even fracture of the valve stem or wedge gate's T-slot.
3. Rigorous Electrical Installation and Calibration
For traditional wedge gate valves, whether manual or electrically operated, there is generally a lack of consideration for position indication devices, making precise setting of switch positions unattainable. Consequently, users must rely on experience and tactile feedback during operation and calibration, often leading to either overtightening or loosening. Overtightening may cause wedging or abrasion of sealing surfaces, while loosening can result in internal leakage. The difficulty in accurately adjusting positions creates inherent risks for valve malfunctions.
4. Downstream Seal Abrasion Risk
A typical failure of these valves is the susceptibility of downstream sealing surfaces to abrasion, leading to early-stage internal leakage. This phenomenon is particularly prevalent in large-diameter or high-pressure differential valves. Major contributing factors include high-temperature adhesive stickiness of sealing surfaces leading to reduced pressure, unbalanced forces due to high pressure differentials acting on one side of the sealing surface, and frictional forces during the opening and closing moments.
5. Cast Housing Leakage Hazard
The housing of wedge gate valves is commonly manufactured using casting processes, which inherently introduces several defects. Materials such as WCB and WC6 are typically used, but the limitations of casting processes result in numerous inherent defects that are challenging to detect through conventional inspection methods. Defects such as sand holes, shrinkage voids, and cracks pose significant risks for external leakage, pipe bursting, and other accidents.
6. High Number of Gate Components and Relatively Weak Structural Integrity
Wedge gate valve gate assemblies consist of over ten components, including upper and lower thrust plates, left and right gates, gate frames, and top cores, among others, resulting in a relatively loose structure. During operation, issues such as root cracking of the valve stem or fractures at pinhole locations, gate detachment, and gate frame fractures may arise, thereby reducing the reliability of the valve.
In conclusion, while wedge gate valves offer advantages in certain aspects, their various defects and issues demand significant attention. Only through comprehensive recognition and resolution of these problems can their safety and reliable operation in industrial production be assured.
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