Valve Stem Packing With Inter-Packing Pressure Equalization
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Solution Overview
Problem
Conventional control valve packing systems face challenges in minimizing fugitive emissions, particularly in high-pressure and high-temperature applications, where increased friction leads to wear and higher operational costs due to the need for larger actuators and more frequent maintenance.
Innovation Solution
The proposed solution involves a packing system with an inter-packing volume exposed to downstream pressure, reducing the pressure differential across the packing system, and utilizing a labyrinth seal with a higher leakage rate upstream to divert excess leakage to downstream systems, thereby reducing friction and emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional packing systems are used to seal around the valve stem, then sealing performance is achieved, but friction increases leading to wear and higher operational costs
Solution Approach 1:
The packing system is divided into multiple packing elements (first packing element, second packing element, third packing element) arranged in series along the valve stem. Each packing element handles a portion of the sealing task, distributing the friction and wear across multiple components rather than concentrating it on a single packing element, thereby reducing overall wear per element while maintaining sealing performance.
Solution Approach 2:
A lubricant delivery system with delivery holes is introduced as an intermediary mechanism between the valve body and packing elements. This system continuously supplies lubricant to the packing elements, reducing friction between the packing elements and the valve stem, thereby maintaining sealing performance while reducing wear and operational costs.
2Ease of operation
If larger actuators are used to overcome friction, then valve operation is maintained, but device complexity and cost increase
Solution Approach 1:
A pressure relief valve is incorporated into the packing system that uses fluid pressure dynamics to automatically relieve excess pressure between packing elements. This pneumatic/hydraulic mechanism reduces the force required to operate the valve by eliminating pressure buildup that would otherwise require larger actuators, thereby maintaining ease of operation while reducing actuator size and system complexity.
3Reliability
If more frequent maintenance is performed to address wear, then reliability is maintained, but productivity decreases
Solution Approach 1:
The packing system incorporates self-lubricating features through the lubricant delivery system with delivery holes that automatically supply lubricant to packing elements during operation. This self-service mechanism continuously reduces wear without requiring external intervention or frequent maintenance shutdowns, thereby maintaining system reliability while maximizing operational time and productivity.
Solution Approach 2:
The lubricant delivery system performs preliminary lubrication of packing elements before significant wear occurs. By continuously supplying lubricant during normal operation, the system prevents wear accumulation that would otherwise require frequent maintenance interventions, thereby maintaining reliability while minimizing downtime and maximizing productivity.
4Stress or pressure
If higher leakage rate packing is used upstream, then pressure differential is reduced, but leakage to downstream increases
Solution Approach 1:
The system converts the potential harm of leakage through the first packing element into a benefit by providing a controlled leakage path through the second packing element to the downstream side. The pressure relief valve captures and redirects this leakage away from the environment, transforming what would be fugitive emissions into a controlled flow that reduces the pressure differential across the packing system, thereby reducing overall stress while managing leakage.
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 approach reduces operational stress on the packing system, minimizes fugitive emissions, and extends the lifespan of the control valve while maintaining effective sealing performance.
Implementation Method 1
an inter-packing volume between the first packing arrangement and the second packing arrangement. A bore port can extend through the bonnet to provide fluid communication between (i) the inter-packing volume and (ii) the outlet of the control valve or a vacuum source, such that the inter-packing volume is exposed to a downstream pressure
Implementation Method 2
A first packing arrangement can be a labyrinth seal configured to have a first leakage rate that is greater than a second leakage rate of a second packing arrangement
Data Source
AI summary
A packing system is disclosed for use with a valve having a bonnet and a flow passage extending between an inlet and an outlet of a valve body. A bore can extend through the bonnet to receive a stem that moves a control member to control flow through the flow passage. A first packing arrangement can be arranged in the bore about a first portion of the stem. A second packing arrangement can be arranged in the bore about a second portion of the stem with the first packing arrangement between the second packing arrangement and the valve body. A bore port can extend through the bonnet and open into an inter-packing volume of the bore between the first and second packing arrangements and can provide fluid communication between the inter-packing volume and the outlet of the valve or other lower pressure area.