Multistage Roots Vacuum Pump Tip Radius Variation
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Solution Overview
Problem
Multistage Roots vacuum pumps face difficulties in achieving high volume ratios without excessively thin rotor components at the exhaust stage, leading to machining and mounting challenges, as well as reduced pumping efficiency due to varying thermal expansions and clearance issues.
Innovation Solution
A multistage vacuum pump design where the tip radius of the rotor components at the exhaust stage is smaller than at the inlet stage, allowing for a high volume ratio of at least 10:1 without reducing rotor thickness to extreme levels, with a progressive reduction in tip radius from inlet to exhaust stages and a pressure relief valve for enhanced operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the volume ratio of the pump is increased to reduce power consumption and generate higher vacuum, then the rotor thickness at the exhaust stage must be reduced, but this makes machining and mounting very difficult and reduces pumping efficiency
Solution Approach 1:
The patent applies local quality by varying the tip radius of rotor components across different stages. The exhaust stage rotor has a smaller tip radius (e.g., 10-20mm) compared to the inlet stage rotor (e.g., 30-50mm), allowing the exhaust stage to achieve the required volume reduction for high vacuum without excessively thinning the rotor thickness. This localized geometric modification enables high volume ratios while maintaining manufacturable rotor thickness.
2Productivity
If the rotor thickness is reduced to achieve high volume ratio, then the pumping efficiency decreases due to varying thermal expansions and clearance issues, but maintaining thick rotors limits the achievable volume ratio
Solution Approach 1:
The patent changes the geometric parameter of tip radius progressively from inlet to exhaust stages. This parameter change allows each stage to have optimized rotor dimensions that maintain adequate thickness for thermal stability and clearance control, while collectively achieving high volume ratio. The progressive reduction in tip radius creates a geometric progression that balances volume reduction with structural integrity.
3Shape
If the tip radius of exhaust stage rotors is reduced to achieve high volume ratio, then the rotor thickness can be maintained at acceptable levels, but the device complexity increases
Solution Approach 1:
The patent segments the rotor assembly into multiple stages with different tip radii. Each stage is designed with appropriate rotor dimensions for its specific pressure and volume requirements. This segmentation allows the system to achieve high overall volume ratio while each individual rotor remains manufacturable and maintainable, distributing the complexity across modular stages rather than requiring one extremely thin rotor.
Data Source
AI summary
A multistage vacuum pump includes a stator housing a multistage rotor assembly, each stage having intermeshing Roots rotor components, wherein the tip radius of the rotor components at an inlet stage of the pump is larger than the tip radius of the rotor components at an exhaust stage of the pump, wherein a meshing clearance between the rotor components at the inlet stage of the pump is greater than a meshing clearance between the rotor components at the exhaust stage of the pump.