Flexible Seal Membrane Assembly for Axial Shaft Shift at High Pressure
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Solution Overview
Problem
Existing mechanical seals in rotary shaft equipment face challenges in sealing higher internal pressures due to axial shifting of the shaft, which causes elastomeric bellows to rigidly collapse, leading to excess face pressure, frictional wear, and eventual seal failure.
Innovation Solution
A non-collapsible flexible sealing membrane with a radially extending flange portion and an axially extending coaxial portion, oriented orthogonally, is integrated into the mechanical seal assembly. This design includes a flexible connecting portion and is held fixed by an annular band and stub sleeve, allowing directional control of forces and maintaining a constant closing force regardless of axial position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an elastomeric bellows is used in a non-pusher seal to reduce torque stress, then the bellows can contract and expand to balance opening and closing forces, but at high pressures the shaft translates axially causing the elastomeric bellows to rigidly collapse, preventing effective counteraction of closing forces
Solution Approach 1:
The patent employs a flexible membrane bellows constructed from flexible materials such as elastomers, fluoropolymers, or PTFE. The membrane structure maintains flexibility at high pressures through its thin-walled construction and geometric design, allowing it to deform axially to counteract shaft translation without rigid collapse. The flexible membrane can expand and contract radially while maintaining axial compliance, resolving the contradiction between needing rigidity to withstand pressure and flexibility to accommodate axial movement.
Solution Approach 2:
The patent changes the physical parameters of the bellows by controlling wall thickness, membrane geometry, and material properties to optimize the balance between radial strength and axial flexibility. By adjusting these parameters, the bellows can withstand high internal pressures while maintaining the ability to deform axially to compensate for shaft movement, thus preventing rigid collapse and maintaining seal performance.
2Strength
If the flexible sealing membrane is made more rigid to withstand high pressures, then it can resist collapse, but it loses the ability to flex and counteract axial shaft movement, leading to excess face pressure and wear
Solution Approach 1:
The flexible membrane bellows uses thin-walled flexible material construction that provides sufficient radial strength to withstand high pressures while maintaining axial flexibility. The membrane geometry and material selection enable the structure to resist radial collapse forces while allowing axial deformation to accommodate shaft movement, thus simultaneously achieving both pressure resistance and adaptability.
Solution Approach 2:
The patent employs composite material structures or material combinations that provide both strength and flexibility. By using materials such as reinforced fluoropolymers, PTFE composites, or multi-layer constructions, the bellows achieves high radial strength to withstand pressure while maintaining the elasticity and flexibility needed to deform axially and counteract shaft translation.
3Reliability
If a pusher seal assembly with dynamic secondary seal is used to provide sealing between shaft and seal members, then sealing is improved, but axial movement of the seal member causes fretting or shredding of the secondary seal due to friction
Solution Approach 1:
The patent eliminates the dynamic secondary seal component entirely by transitioning to a non-pusher seal configuration. The flexible membrane bellows directly provides the sealing function without requiring a separate dynamic secondary seal that would be subject to fretting and shredding from axial movement. This extraction of the problematic component resolves the contradiction between sealing effectiveness and component durability.
Solution Approach 2:
The flexible membrane bellows serves as an intermediary element that provides both the sealing function and the axial compliance needed to accommodate shaft movement without causing friction wear. Instead of allowing direct contact and relative motion between rigid components that causes fretting, the flexible membrane mediates the interaction, providing sealing while deforming to absorb axial movement, thus extending component lifespan.
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 flexible sealing membrane effectively reduces the impact of axial shifting at high pressures, preventing collapse and maintaining seal performance by ensuring consistent closing forces and minimizing leakage and wear.
Implementation Method 1
an elastomeric bellows, an example of which is provided in FIG. 1. The depicted mechanical seal comprises an elastomeric bellows that is driven to rotate with the shaft relative to the housing. This non-pusher seal can reduce torque stress on the bellows, which are intended to contract and expand to balance the opening and closing forces on the seal faces.
Implementation Method 2
various biasing mechanisms have been contemplated to provide a closing force to automatically accommodate wear. Such biasing mechanism have included single and multiple coil springs
Data Source
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AI summary
A non-collapsible flexible sealing membrane (or bellows) (100) for incorporation in a mechanical seal assembly and use in rotary shaft equipment. The sealing membrane includes a substantially radially outward extending first flange portion (102), which can be urged into an axially shiftable ring (36) by a biasing mechanism (500). The sealing membrane further includes a substantially axially outboard extending second coaxial portion (104), substantially radially inward of the balance diameter of the seal. The coaxial portion is advantageously held fixed to a stub sleeve (200) by an annular band (300). The angle between the flange portion and the coaxial portion of sealing membrane enables directional control of the forces acting on stub sleeve and first ring.