Gate Valve Stem Anti-Rotation Assembly for Wedge Pin Shear Prevention
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Solution Overview
Problem
Double disc gate valves in nuclear reactor power plants experience stem-disc separation due to shear failure of the wedge pin and excessive wear of the valve stem-to-wedge threads, leading to costly and time-consuming repairs.
Innovation Solution
An anti-rotation device is installed on the valve stem using an extension bolted to the stem with a housing mounted on the actuator, featuring an anti-rotation assembly that prevents stem rotation and torque application at the stem-to-wedge joint, allowing for in-situ installation without valve or actuator disassembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a wedge pin is used to prevent stem loosening, then stem separation is prevented, but the wedge pin is subject to shear failure due to actuator torque
Solution Approach 1:
A torque arm is introduced as an intermediary component between the actuator and the stem. The torque arm receives the actuator torque and transmits it to the stem through a pinned connection, preventing the wedge pin from directly bearing the full actuator torque while still preventing stem loosening
Solution Approach 2:
The anti-rotation function is extracted from the wedge pin and assigned to a separate torque arm component. This allows the wedge pin to focus solely on preventing stem loosening while the torque arm handles the torque transmission and anti-rotation functions
2Ease of operation
If the stem is allowed to rotate during operation, then valve operation is simplified, but excessive wear occurs on the stem-to-wedge threads
Solution Approach 1:
The torque arm acts as an intermediary that provides the necessary anti-rotation function without requiring the wedge pin to bear torque, thereby eliminating excessive thread wear while maintaining simplified valve operation
Solution Approach 2:
The functions of torque transmission and stem retention are segmented into separate components (torque arm and wedge pin respectively), allowing each component to be optimized for its specific function without compromising the other
3Reliability
If repair is performed after wedge pin failure, then valve functionality is restored, but extensive disassembly and high costs are required
Solution Approach 1:
The torque arm is pre-installed on the stem before final assembly, with the actuator torque automatically transferred to the torque arm during initial operation. This preliminary configuration prevents wedge pin failure before it occurs, eliminating the need for complex repairs
Solution Approach 2:
The torque arm serves as a protective intermediary that prevents the wedge pin from experiencing shear loads that would lead to failure, thereby preventing the need for extensive disassembly and repair operations
Data Source
AI summary
An anti-rotation device for preventing separation of a valve stem and valve disc(s) in a gate valve in a nuclear reactor power plant of the type where connection means, such as a wedge or disc hub, is threadedly engaged by the valve stem to actuate the valve and a method for maintenance or repair of the valve without disassembly of the valve or removal of the valve actuator.