Handling Valve Core Detachment in Rising Stem Wedge Gate Valves

 
Rising stem wedge gate valves are commonly used in industries such as oil, chemical, and water treatment. Their primary function is to control the flow of fluid through a pipeline by raising or lowering the valve core, effectively allowing or blocking the passage of the medium. However, in practice, issues such as corrosion, wear, or improper operation can cause the connection between the valve stem and the valve core to fail, leading to valve core detachment. This problem can affect the normal operation of the gate valve and even pose safety risks. Therefore, it is crucial to address valve core detachment promptly and effectively.

Common Causes of Valve Core Detachment

 
Valve core detachment is a frequent issue in industrial applications, and it can be caused by several factors:
 
Corrosion: When the valve is exposed to corrosive media for an extended period, the connection between the valve stem and valve core is prone to corrosion, leading to failure.
 
Wear: The frequent opening and closing of the valve can cause friction between the valve stem and valve core, resulting in wear and eventually causing the connection to become loose or break.
 
Improper Operation: Excessive operating force or incorrect operation direction can cause uneven stress at the connection point between the valve stem and valve core, leading to detachment.

Methods for Handling Valve Core Detachment

 
When a rising stem wedge gate valve experiences valve core detachment and cannot be isolated from the system, the following steps can typically be taken to repair it. By keeping the valve body, core, and seat stationary, and adjusting the assembly of the valve bonnet, stem, bronze bushing, packing, and gland, the valve core can be exposed, and the stem and valve core can be reconnected. This method effectively restores the valve's normal function without the need for complex operations such as shutting down the system or rerouting.

1. Preparation

 
Before proceeding with the repair, it is important to confirm that the seal between the valve core and seat is intact. Ensuring no leakage of the medium allows for the repair to be completed in a short time without affecting the site operations.

2. Disassembly Steps

 
Loosen the Packing Gland: First, unscrew the nuts on the packing gland and loosen the packing to allow free movement of the valve stem.
 
Loosen Bonnet Nuts: Loosen all the nuts on the bolts of the valve bonnet a few turns, but do not remove them completely.
 
Separate the Bonnet: Continue to turn the handwheel in the closing direction. At this point, the valve stem will no longer move, but the parts above the bonnet will separate from the valve body. This step is to check the seal between the valve core and seat. If the seal is not tight and there is some leakage, but it does not significantly affect the operation, proceed with the repair.

3. Inspection and Repair

 
Expose the Valve Core: Completely unscrew the nuts on all the bolts and remove the upper part of the bonnet and the valve stem to expose the top of the valve core. Inspect the original connection method between the valve stem and valve core and identify the cause of the failure to develop a solution.
 
Repair or Replace the Valve Stem: Reconnect the removed valve stem with the valve core, usually by welding. This method is suitable for non-flammable media such as water, air, and steam lines. For valves used with oil and gas media, direct welding is not safe. Instead, the valve stem end should be removed and processed into a special form as needed. When installing, the contact surface between the valve stem and valve core can be treated with high-strength adhesive or by drilling and tapping the top of the valve core for threading and connecting the valve stem.

4. Reassemble the Valve

 
Assembly Steps: Ensure that the installation plane of the valve stem and bonnet is vertical and well-aligned. Otherwise, opening the valve after repair may cause the stem to bend or become difficult to operate. After connecting the valve stem, install the bonnet, some packing, the gland, and the stem nut in sequence, replacing the gasket if necessary to prevent leaks from the sealing surface. Once the bonnet is in place, align the bolt holes on the valve body and tighten the bolts symmetrically.
 
Adjust the Packing: Add additional packing to the stuffing box as needed and tighten the packing gland appropriately. Finally, fit the handwheel onto the stem nut and secure it with a locknut to complete the repair.

Precautions and Conclusion

 
When dealing with valve core detachment, it is essential to pay attention to the following points:
 
Operational Safety: During the repair process, strictly follow safety protocols, especially when handling valves for oil and gas media. Fire and explosion prevention measures must be taken to ensure safety.
 
Repair Quality: After reconnecting the valve stem and valve core, ensure that the installation plane is vertical and well-centered to avoid affecting the valve's subsequent use.
 
Regular Maintenance: Regular inspection and maintenance of valves are essential to identify and address corrosion, wear, and other issues promptly, preventing problems such as valve core detachment.
 
Through proper maintenance and timely repairs, rising stem wedge gate valves can remain reliable and durable, reducing the risk of unexpected shutdowns and associated economic losses. Correct operation and regular inspections not only extend the service life of the valves but also ensure equipment safety and operational efficiency. In practice, mastering the emergency handling methods for valve core detachment and implementing them effectively can prevent accidents, ensure continuous process flow, and maintain system stability. This not only helps to improve production efficiency but also provides strong support for the safety management of enterprises.