Biased Longitudinal Stator Seals for Vacuum Pump Leakage Control
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Solution Overview
Problem
In vacuum pumps with horizontally split stators, the longitudinal seal groove is wider than the seal, leading to undefined seal location and potential gas leakage between the pump ends due to thermal expansion, as the seal may not lie against the inner surface, creating a gap and leakage path.
Innovation Solution
A longitudinal seal with a deviation configured to abut against the outer surface of the groove, biasing the seal towards the inner surface, ensuring proper location and sealing without modifying the stator or groove, and maintaining a substantially constant cross section to allow for uniform expansion and prevent pinch points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the seal groove is made wider than the seal to allow for thermal expansion and compression, then the seal can accommodate temperature changes, but the seal location becomes undefined and gas leakage paths are created
Solution Approach 1:
The seal is divided into two functional zones: a central sealing region with constant cross-section that maintains reliable sealing, and end regions with increased cross-section that provide thermal expansion accommodation and biasing forces. This segmentation allows each zone to perform its specific function optimally.
Solution Approach 2:
Different portions of the seal have different cross-sectional properties. The central portion has a smaller, constant cross-section for reliable sealing, while the end portions have larger cross-sections that expand more with temperature to provide biasing forces. This local differentiation resolves the contradiction between sealing reliability and thermal adaptability.
2Reliability
If the seal has varying cross section to provide biasing forces, then seal location is improved, but pinch points are created due to differential expansion
Solution Approach 1:
The seal is segmented into a central constant cross-section region and end variable cross-section regions. The constant cross-section central region avoids pinch points and maintains seal integrity, while the end regions provide the necessary biasing forces through controlled expansion.
Solution Approach 2:
The seal employs local quality variation where only the end portions have increased cross-section for biasing, while the central sealing region maintains uniform cross-section to prevent pinch points and ensure consistent sealing performance throughout operation.
3Reliability
If bumps are added to the housing to bias the seal, then seal location is improved, but modifications to the housing are required and overcompression may occur
Solution Approach 1:
The seal structure itself provides the biasing function through its own material properties and geometry. The enlarged end portions of the seal expand with temperature to naturally bias the seal toward the correct position, eliminating the need for external biasing features in the housing and reducing overall device complexity.
Solution Approach 2:
The seal performs multiple functions: sealing, thermal expansion accommodation, and self-biasing. By integrating the biasing function into the seal structure itself rather than requiring separate housing features, the solution reduces complexity while achieving reliable seal positioning.
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 blocks potential leakage paths and maintains consistent sealing performance across temperature changes, ensuring reliable vacuum operation by using the elastomeric properties of the seal to maintain proper positioning and prevent overcompression.
Implementation Method 1
the elastomeric properties of the seal provide the biasing force
Implementation Method 2
where it is formed to have a substantially constant cross section then when the seal expands due to temperature increases, the expansion will be substantially the same along the deviation
Data Source
Figure 1~2
Figure 3a~3b
Figure 4
AI summary
A vacuum pump and method of manufacture thereof, the vacuum pump comprising: two half shell stators components mounted together at longitudinal contact faces and defining one or more pumping chambers; longitudinal seals for sealing between the longitudinal contact faces of the two half shell stators on either side of the pumping chamber. The longitudinal seals are mounted within respective grooves in at least one of the half shell stators, the respective grooves being wider than the longitudinal seal over at least a portion of the longitudinal seal allowing for some lateral movement. The longitudinal seal comprises a deviation from a longitudinal axis, the deviation abutting against one surface of the groove and biasing at least a portion of the longitudinal seal towards an opposite surface of the groove, the opposite surface comprising the surface closest to the pumping chamber.