Centrifugal Pump Impeller Apertures for Down Thrust Reduction
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Solution Overview
Problem
Abrasive particles in well fluids cause wear on impeller and diffuser surfaces, leading to increased annular clearance and reduced differential pressure, resulting in increased down thrust and production loss in centrifugal well pumps.
Innovation Solution
The design incorporates a bottom shroud with apertures, such as notches, on the circumference of the impeller, which reduce down thrust on the down thrust washer without affecting hydraulic performance, by creating a serrated edge and varying radial clearance with the diffuser inlet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If abrasive particles cause wear on the skirt and diffuser surfaces, then the annular clearance increases, but the differential pressure across the skirt seal area reduces and down thrust increases
Solution Approach 1:
The bottom shroud is segmented with multiple apertures distributed around its circumference. These apertures divide the continuous shroud surface into separate segments, allowing pressure equalization while maintaining structural integrity. The segmentation enables different regions of the shroud to experience different pressure conditions, reducing the net down thrust force on the impeller assembly.
Solution Approach 2:
The apertures in the bottom shroud act as intermediary channels that mediate pressure transmission between the upper and lower sides of the shroud. By providing these intermediate pressure equalization paths, the apertures reduce the pressure differential that would otherwise act directly on the bottom shroud surface, thereby reducing down thrust without compromising the seal function.
2Loss of substance
If the annular clearance increases due to wear, then leakage increases, but the pressure differential across the skirt seal area reduces
Solution Approach 1:
The apertures are pre-configured in the bottom shroud design to provide pressure equalization paths before wear occurs. This preliminary action ensures that even when the skirt clearance increases due to wear, the pressure differential is already being managed through the apertures, preventing the exponential increase in leakage that would otherwise occur with larger clearances.
3Force
If apertures are added to the bottom shroud to reduce down thrust, then the structural complexity increases, but the hydraulic performance must be maintained
Solution Approach 1:
Rather than modifying the entire bottom shroud structure, the invention applies local modifications in the form of apertures at specific locations on the shroud surface. These localized changes provide the necessary pressure equalization function without requiring comprehensive structural redesign, thus minimizing the increase in overall device complexity while achieving down thrust reduction.
Data Source
AI summary
A submersible well pump assembly includes a pump driven by a motor. The pump has a number of stages, each stage including a diffuser having an annular diffuser inlet with an annular outer wall. Diffuser passages lead downstream and inward from the diffuser inlet. An impeller has a circumferential outer edge adjacent the outer wall of the diffuser inlet. Notches are formed in the circumferential outer edge, defining a serrated configuration.