The gate valve's opening and closing component is the gate disc, which is typically circular and positioned inside the valve body. It moves up and down vertically along the centerline of the valve seat under the control of the valve stem.
- When the gate lowers, it fits tightly against the seat, shutting off the valve and completely blocking the fluid passage.
- When the gate rises, it separates from the seat, opening the valve and allowing fluid to flow freely.
By adjusting the height of the gate, the flow rate of the medium can be effectively controlled. This simple and reliable mechanical design makes the gate valve one of the most commonly used shut-off valves today.
Structure and Classification of Gate Valves
Based on the structure of the gate disc, gate valves can be categorized into the following types:
1. Parallel Gate Valve
This type features two parallel discs. During closure, a bottom wedge pushes the discs outward, pressing them tightly against the guide holes on both sides of the valve seat to achieve sealing.
The main advantage of this structure lies in its simplicity of manufacture; however, its sealing performance is relatively weaker.
2. Wedge Gate Valve
The wedge-shaped gate forms a certain angle with the valve seat, enhancing sealing performance through a wedging effect.
This structure offers better sealing and is widely used in applications with higher sealing requirements. However, it is relatively more complex to manufacture and maintain.
Wedge gate valves can be further classified into three types: solid wedge, double wedge, and resilient wedge.
3. Resilient Gate Valve
This type uses a gate disc made from elastic material, which allows for slight deformation during closure to improve sealing performance.
Combining the benefits of both parallel and wedge designs, it offers good sealing and reliable operation, making it one of the most commonly used gate valve structures today.
Advantages and Disadvantages of Gate Valves
Advantages:
- Minimal flow resistance, resulting in virtually no pressure loss;
- Requires relatively low torque for opening and closing, making it easy to operate;
- Can be installed in both directions; the flow direction is not restricted;
- No water hammer effect when closing;
- Relatively simple structure with mature manufacturing processes.
Disadvantages:
- Requires a larger installation height and occupies more space;
- Slower opening and closing times, making it unsuitable for frequent operation;
- The sealing surfaces are prone to wear during opening and closing;
- Maintenance is relatively more complex, and repair or replacement can be costly.
Difference Between Rising Stem and Non-Rising Stem Gate Valves
Based on the structure of the valve stem, gate valves can be further categorized into rising stem and non-rising stem types.
- Rising Stem Gate Valve: The stem is exposed and rises as the valve opens, allowing for a clear visual indication of the valve’s open or closed position. This makes operation and maintenance easier. However, its overall height increases with the opening degree, making it more suitable for installations with ample vertical space
- Non-Rising Stem Gate Valve: The stem is concealed within the valve body, resulting in a more compact structure that is ideal for confined spaces. However, the valve’s open or closed status cannot be directly observed, which limits visibility during operation.
Conclusion
In summary, gate valves control fluid flow by means of the vertical movement of a gate disc, with various structural designs enabling effective shut-off functionality. Thanks to their low flow resistance, strong sealing capabilities, and wide applicability, they are extensively used in industries such as water treatment, power generation, petrochemicals, and metallurgy.However, proper valve selection should be based on specific operating conditions, media type, and space limitations to ensure long-term and stable system performance.
Frequently Asked Questions (Q&A)
Q1: Is a gate valve suitable for regulating flow?A: Not recommended. Gate valves are primarily designed for on/off control and are not ideal for frequent throttling, which can lead to excessive wear of the sealing surfaces.
Q2: Which is better — rising stem or non-rising stem gate valve?
A: It depends on the available installation space. Rising stem valves are easier to monitor and operate, making them ideal for areas with ample space. Non-rising stem valves offer a compact design, suitable for confined installations.
Q3: Why does a gate valve sometimes leak when closed?
A: Possible causes include worn sealing surfaces, debris obstructing the seat, or the gate not fully pressing against the seat. Regular inspection and timely maintenance of sealing components are advised.
Q4: Can a gate valve be installed on a horizontal pipeline?
A: Yes, but the valve stem must remain in a vertical upward position. Tilted installation should be avoided to ensure proper operation and tight sealing.
