Eccentric Wear Rings for Centrifugal Pump Shaft Deflection
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Solution Overview
Problem
Multi-stage horizontal centrifugal pumps face issues with physical contact between the rotor and wear rings, especially when stationary, leading to reduced efficiency and increased wear, due to shaft deflection and gravitational forces, which complicates maintenance and operation.
Innovation Solution
The implementation of eccentrically configured wear rings that compensate for shaft deflection without requiring significant design changes to other pump components, allowing the rotor to rotate freely at standstill and maintain efficiency by ensuring adequate clearance without increasing leakage flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the clearance between wear rings and shaft is increased to avoid physical contact during shaft deflection, then the rotor can rotate freely at standstill, but the pump efficiency decreases due to increased leakage flow
Solution Approach 1:
The wear ring is designed with an asymmetric cross-section where the thickness varies around the circumference. The thicker portion is positioned to compensate for shaft deflection, ensuring adequate clearance when the shaft deflects under gravitational force, while the thinner portion maintains smaller clearance to minimize leakage flow during normal operation, thus resolving the contradiction between rotor rotation freedom and pump efficiency
Solution Approach 2:
Different portions of the wear ring have different thicknesses to address different operational requirements at different locations. The local thickness variation allows the wear ring to provide adequate clearance where shaft deflection occurs while maintaining tight clearance in other areas to minimize leakage, thereby balancing rotor freedom of operation with pump efficiency
2Productivity
If the clearance between wear rings and shaft is reduced to maintain pump efficiency, then leakage flow is minimized, but the rotor comes into physical contact with wear rings during shaft deflection at standstill
Solution Approach 1:
The asymmetric cross-section of the wear ring with strategically positioned thicker portions provides the necessary clearance compensation for shaft deflection only where and when needed, while maintaining tight clearances elsewhere to preserve pump efficiency, thus resolving the contradiction between efficiency and rotor freedom
3Ease of manufacture
If conventional symmetric wear rings are used, then manufacturing is simpler, but the rotor experiences physical contact and increased wear during operation due to shaft deflection
Solution Approach 1:
While the asymmetric cross-section requires slightly more complex manufacturing compared to symmetric wear rings, the design still maintains relative simplicity through standardized forming processes. The significant benefit of extended wear ring service life and reduced rotor-wear ring contact during operation justifies the moderate increase in manufacturing complexity, effectively resolving the contradiction between ease of manufacture and reliability
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 prevents physical contact between the rotor and wear rings at all operating states, enhances maintenance accessibility, and maintains pump efficiency by minimizing clearance and avoiding costly modifications to stage housings or seals.
Implementation Method 1
an annular gap is formed between the radially inner, cylinder jacket-shaped boundary surface of the wear ring and the rotating outer jacket surface of the shaft, through which a leakage flow from the high-pressure side to the low-pressure side is made possible. This leakage flow is advantageous on the one hand because it contributes to the hydrodynamic stabilization of the rotor (shaft with impellers)
Data Source
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AI summary
A multi-stage horizontal centrifugal pump for conveying a fluid is proposed, comprising a rotor (6, 32) which includes a rotatably arranged shaft (6) and several impellers (32) for conveying the fluid, wherein all impellers (32) are arranged non-rotatably on the shaft (6), and a stator (31, 33) which includes several stage housings (31) which are arranged one behind the other with respect to an axial direction defined by a central axis (A), wherein the stator (31, 33) surrounds the rotor (6, 32), and wherein all stage housings (31) are designed and arranged concentrically with respect to the central axis (A), and wherein several wear rings (7, 8) are provided between the rotor (6, 32) and the stator (31, 33), each of which is fixed with respect to the stator (31, 33), and each of which secures the rotor (6, 32) with a clearance (S1, S2) surrounds, and wherein at least one of the wear rings (7, 8) is eccentrically designed.Furthermore, a method for repairing a multi-stage horizontal centrifugal pump is proposed.