Bolted Valve Stem Plug Assembly Anti-Loosening
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Solution Overview
Problem
Conventional sliding stem fluid flow control devices face issues with loosening due to process vibrations and cracking of pin-type or welded connections, which affect the reliability of anti-rotation devices.
Innovation Solution
A control element for fluid flow control devices featuring a stem with a fastener recess and a plug assembly that includes a compression cap and seal member, where the fastener engages internal threads to compress the seal member radially, providing a secure and leak-tight seal without the need for welding or press-pinning, and includes anti-rotation features to maintain alignment and prevent rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pin-type or welded connections are used to prevent rotation, then anti-rotation function is achieved, but reliability deteriorates due to loosening from vibrations or cracking
Solution Approach 1:
The connection is divided into multiple threaded fastener elements distributed around the circumference, replacing the single pin or weld with multiple discrete fastening points. This segmentation distributes the mechanical loads and prevents rotation through cumulative friction and geometric constraint, improving reliability without compromising strength.
Solution Approach 2:
The pin-type or welded mechanical connection is replaced with a threaded fastener system that uses screw threads to create a clamping force. This substitution eliminates the loosening issue of pins and cracking issue of welds by using a mechanical threading system that maintains constant clamping pressure and can be easily inspected and replaced.
2Ease of manufacture
If conventional threaded shaft connections are used, then assembly is simplified, but anti-rotation reliability deteriorates under vibration
Solution Approach 1:
The fastener system incorporates asymmetric features such as non-circular fastener heads or slots that prevent rotation in one direction while allowing assembly. The threaded engagement combined with asymmetric anti-rotation features creates a connection that is both easy to assemble and highly reliable under vibration, as the asymmetric geometry provides inherent resistance to loosening.
3Reliability
If seal member compression is increased to improve sealing, then leak-tightness is achieved, but radial expansion requirements increase
Solution Approach 1:
The seal member is designed as a flexible element that can be compressed axially between the compression cap and plug body. This flexible membrane or ring expands radially under compression to create a leak-tight seal against the inner surface of the cage, achieving high sealing reliability while maintaining sufficient strength through the material's elastic properties and geometric design.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances the reliability and durability of fluid flow control devices by providing a secure, leak-tight seal and preventing rotation, reducing wear and increasing the useful life of components, while eliminating the need for welding or press-pinning, thus addressing the issues of loosening and cracking.
Implementation Method 1
the engagement between the fastener and the fastener recess compresses the seal member between the compression cap and the plug body, such that the seal member expands radially and sealingly engages an inner surface of the cage
Data Source
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AI summary
A control element (12) for a fluid flow control device includes a stem (18), a plug (20), and a fastener (22). The stem includes an elongated member with a first end (18a) and a second end (18b). The first end is adapted to be operably coupled to an actuator and the second end including a fastener recess (24) including a plurality of internal threads (38). The plug is disposed adjacent to the second end of the stem. The fastener fixing the plug to the stem includes a threaded portion (64) extending from the plug and engaging the plurality of internal threads of the fastener recess.