Stem Seal With Triangle-Sectional Bushing and Spherical Socket
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Solution Overview
Problem
Conventional stem seals for movable stems, particularly in valves, face challenges in maintaining effective sealing under varying operational and non-operational loads, leading to leaks and reduced reliability, as they rely on axial compression to achieve radial sealing, which can result in uneven stress distribution and material exhaustion, failing to meet stringent pressure ratings and reliability standards.
Innovation Solution
A stem cylinder seal using a triangle-sectional bushing or ring fully compressed between two conical sockets, and a stem shoulder seal with a ball wedge/spherical socket mating arrangement, allowing for even radial compression and resistance to wear, eliminating the need for stuffing box restrictions and enabling the seals to withstand pressures up to 1.5 times the valve rating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional packing rings are compressed axially to achieve sealing, then the stem cylinder seal is formed, but the sealing stress is unevenly distributed and material strength is exhausted
Solution Approach 1:
The invention employs a spherical stem end instead of a conventional cylindrical stem end. This spherical geometry allows the packing rings to be compressed uniformly around the stem, distributing the sealing stress evenly across all packing rings. The spherical shape eliminates stress concentration points and ensures that each packing ring experiences equal compressive force, thereby improving sealing reliability without exhausting material strength.
Solution Approach 2:
The invention changes the geometric parameter of the stem end from cylindrical to spherical. This parameter change fundamentally alters the stress distribution pattern during compression. The spherical geometry transforms the stress distribution from uneven (with stress concentration at certain points) to uniform (evenly distributed around the entire circumference), allowing the packing material to withstand higher pressures without exceeding its strength limits.
2Force
If axial compression is applied to packing rings, then radial sealing force is generated, but the compression force is inefficiently converted
Solution Approach 1:
The spherical stem end geometry optimizes the conversion of axial compression force into radial sealing force. When axial force is applied to the spherical stem end, it uniformly distributes this force radially outward against the packing rings. This geometric configuration maximizes the efficiency of force conversion, ensuring that the entire axial compression force is effectively transformed into radial sealing pressure without loss, unlike conventional cylindrical designs where force distribution is uneven.
3Reliability
If conventional cylindrical stem end is used, then the structure is simple, but the sealing performance deteriorates under varying loads
Solution Approach 1:
The spherical stem end replaces the conventional cylindrical stem end, providing superior sealing performance under varying operational and non-operational loads. The spherical geometry naturally accommodates load variations by maintaining uniform contact and stress distribution throughout the packing rings, regardless of the direction or magnitude of the applied forces. This simple geometric change delivers robust sealing performance without requiring complex additional components or mechanisms.
4Reliability
If stuffing box restrictions are used to compress packing, then the seal is contained, but the compression is uneven and restrictive
Solution Approach 1:
The invention extracts and eliminates the stuffing box restriction from the sealing system. By removing the confining stuffing box, the packing rings are free to expand and conform to the spherical stem end under compression without being constrained by rigid walls. This extraction of the restrictive element allows for more uniform and natural compression of the packing material, improving both the ease of operation and the overall seal integrity.
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 provides a high-efficiency, wear-resistant, and reliable stem seal assembly that doubles the strength of the sealing material, meeting ASME and TA Luft standards by evenly distributing radial forces and maintaining integrity under temperature and pressure changes.
Implementation Method 1
The stem cylinder seal is a triangle-sectional bushing or ring of stem cylinder seals compressed fully within two opposing conical sockets... A radial force compounded by the compressing force from the gland and the reacting force from the lower conical socket is applied to the cylindrical outer surface
Implementation Method 2
The stem shoulder seal is a ball wedge/spherical socket mating arrangement... the spherical shoulder is so diametrically either equal to or economically slightly bigger than the spherical socket... the mating contact will be always on the spherical surface
Implementation Method 3
The packing can only be compressed by an originally axial force. Thus it is critical for realizing the stem cylinder seal to enable the packing to obtain a radially compressing component from an originally axially compressing force
Data Source
AI summary
Any stem seal using either a triangle-sectional bushing or ring as stem cylinder seals or a ball wedge/spherical socket mating arrangement as stem shoulder seals can individually withstand the same pressure as the burst pressure of bodies without failure. The sectional triangle of the triangle-sectional bushing or ring is truncated to provide a wearing and compressing allowance for the bushing or ring, and so will be again a full triangle or an untruncated triangle when the bushing or ring is fully worn. The ball wedge/spherical socket mating is a mating which uses ball wedges as a stop shoulder of stems and the spherical socket as a stop socket at stem exits.