Control Valve Trim Assembly for Low-Thrust Class V Sealing
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Solution Overview
Problem
Conventional control valves face challenges in maintaining a Class V seal without requiring high actuator thrust, especially at temperatures above the usable limits of elastomeric or thermoplastic materials, which results in high friction and increased actuation requirements.
Innovation Solution
A trim assembly with a low friction flow restrictor and a high friction pressure energized seal, where the seal balancing volume is pressurized to reduce the pressure differential acting on the seal, minimizing friction and actuator thrust by allowing upstream pressure to flow into the seal balancing volume at a controlled rate, reducing leakage through the flow restrictor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a piston ring seal is used to achieve Class V shutoff at high temperatures, then sealing performance is improved, but friction increases resulting in high actuator thrust requirements
Solution Approach 1:
A low friction flow restrictor is introduced as an intermediary component between the piston ring seal and the downstream environment. This flow restrictor allows controlled leakage that prevents excessive pressure buildup behind the seal, thereby reducing the contact pressure and friction between the piston ring seal and the valve plug, while still maintaining Class V sealing performance.
Solution Approach 2:
The invention changes the pressure parameter in the seal balancing volume by allowing controlled fluid flow through the low friction flow restrictor. This pressure modulation reduces the contact pressure between the seal and sealing surfaces, thereby reducing friction and actuator thrust requirements while maintaining sealing effectiveness.
2Reliability
If contact pressure is increased to meet Class V leakage requirements, then sealing performance is improved, but friction increases making valve operation difficult
Solution Approach 1:
The low friction flow restrictor acts as a mediator that regulates the pressure in the seal balancing volume. By controlling the fluid flow through this restrictor, the system maintains optimal contact pressure for Class V sealing while preventing excessive pressure that would increase friction and hinder valve operation.
Solution Approach 2:
The system uses the valve's own operating fluid to automatically regulate the pressure in the seal balancing volume through the low friction flow restrictor. This self-regulating mechanism ensures optimal sealing contact pressure without requiring external control systems, maintaining both sealing performance and ease of operation.
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
This solution effectively reduces the actuator thrust required to open and close the valve while maintaining a tight seal, meeting Class V leakage standards without excessive friction, even at elevated temperatures.
Implementation Method 1
A typical piston ring seal may generate considerable friction while in contact with its sealing surface
Implementation Method 2
minimizing friction and actuator thrust by allowing upstream pressure to flow into the seal balancing volume at a controlled rate, reducing leakage through the flow restrictor
Data Source
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AI summary
A trim assembly is provided with a cage with an internal surface and a cage port. A plug having an external surface is disposed in the cage and is operable between a closed position, a pressure balancing position and an open position. The trim assembly also includes a low friction flow restrictor disposed between the cage and the plug and a pressure energized seal disposed between the cage and the plug. A seal balancing volume defined by the internal surface of the cage, the external surface of the plug, the low friction flow restrictor and the pressure energized seal is provided. The seal balancing volume is in fluid communication with the cage port through the low friction flow restrictor and is maintained at a seal balancing volume pressure. The trim assembly further includes a pressure control assembly configured to vent the seal balancing volume.