Two-Stage Liquid Ring Vacuum Pump Cantilever Shaft Design
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Solution Overview
Problem
Conventional two-stage liquid ring vacuum pumps with cantilever structures suffer from whirling vibrations and resonance due to long rotating shafts, and face challenges in forming sealed blade chambers without increasing the diameter of the main shaft or boss diameter of the impeller, leading to performance degradation and resonance issues.
Innovation Solution
The design features a first-stage impeller with a larger outer diameter than the second-stage impeller, allowing for a shorter rotating shaft and higher natural frequency, while maintaining sealed blade chambers without dividing the exhaust casing or increasing the main shaft diameter, by using impellers with different specifications such as outer diameters, blade number, and thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the rotating shaft is supported at both axial end portions by bearings, then the vacuum pump can be structurally stable, but the entire length of the vacuum pump becomes long
Solution Approach 1:
The invention extracts and eliminates one of the two bearings from the support structure. Instead of supporting the rotating shaft at both axial end portions with bearings, the shaft is supported only at one end by a single bearing, while the other end is freely suspended. This extraction of the unnecessary bearing reduces the overall length of the vacuum pump while maintaining operational stability through the cantilever configuration.
Solution Approach 2:
The invention inverts the conventional support approach by using a cantilever structure instead of a fully supported dual-bearing configuration. The rotating shaft is fixed at one end and left free at the other, reversing the traditional approach of supporting both ends. This inversion enables miniaturization while maintaining functional stability.
2Speed
If the motor is changed from a four-pole motor to a two-pole motor to increase rotational velocity, then the diameter of the impeller can be made smaller, but the shaft power becomes excessively large
Solution Approach 1:
The invention applies local quality by using a two-pole motor that provides high rotational velocity specifically at the impeller stage, while the overall system design (including the cantilever shaft structure and impeller configuration) locally manages the power characteristics. This allows the impeller to operate at high speed for miniaturization while the system architecture prevents excessive shaft power by optimizing the power transmission path and reducing rotational inertia through the shortened shaft design.
3Productivity
If the width of the first-stage impeller is made larger than the second-stage impeller to increase exhaust velocity, then the pumping performance is improved, but the rotating shaft becomes longer causing whirling vibration
Solution Approach 1:
The invention applies asymmetry by making the first-stage impeller width larger than the second-stage impeller width, creating an asymmetric configuration that optimizes exhaust velocity at the vacuum side while maintaining a shorter overall shaft length. This asymmetric design allows the majority of the impeller width increase to be concentrated at the first stage where it is most effective for exhaust velocity, rather than uniformly increasing shaft length throughout.
Solution Approach 2:
The invention transitions from a uniform shaft design to a dimensional optimization where the impeller widths are differentiated along the shaft axis. By making the first-stage impeller wider than the second-stage impeller, the design exploits the dimensional variation along the shaft length to achieve high exhaust velocity without proportionally increasing the overall shaft length, thus avoiding whirling vibration.
4Strength
If the main shaft diameter is increased to prevent impeller contact with casing, then the shaft strength is sufficient, but the blade chambers communicate with each other through the shaft seal housing space
Solution Approach 1:
The invention replaces the mechanical solution of increasing main shaft diameter with a different mechanical approach: using a shorter cantilever shaft configuration that achieves sufficient strength through optimized geometry rather than increased diameter. This substitution allows the shaft seal housing space to remain small enough to prevent blade chamber communication while maintaining adequate shaft strength through the shortened, optimized design.
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 configuration prevents whirling vibrations, maintains high natural frequency, and ensures stable operation by shortening the rotating shaft and preventing blade chamber communication through the shaft seal housing space, thus avoiding resonance and performance degradation.
Implementation Method 1
a liquid film (liquid ring) is formed along an inner wall of the casing by a centrifugal force caused by rotation of the impeller
Implementation Method 2
pumping action is performed by utilizing volumetric change of a blade chamber formed by the liquid film and adjacent two blades
Data Source
AI summary
The present invention relates to a two-stage liquid ring vacuum pump in which two-stage impellers are attached to an axial end portion of a main shaft (rotating shaft) of a motor. The two-stage liquid ring vacuum pump includes a first-stage impeller (4) provided in a first-stage pump chamber (1), a second-stage impeller (5) provided in a second-stage pump chamber (2), a single rotating shaft (7) to which the first-stage impeller (4) and the second-stage impeller (5) are fixed, and an exhaust port (Pd) of the first-stage pump chamber (1) and an intake port (Ps) of the second-stage pump chamber (2) which communicate with each other. An outer diameter of the first-stage impeller (4) is larger than an outer diameter of the second-stage impeller (5).