Centrifugal Pump Impeller Balancing Holes for Seal Protection
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Solution Overview
Problem
Centrifugal pumps face issues with negative pressure in the sealing space, leading to seal damage and air leakage when operating at capacities higher or lower than the optimal range, due to inadequate balancing of pressures behind the impeller, which affects the lubrication and integrity of shaft seals.
Innovation Solution
The impeller design features balancing holes located in the shroud with openings on the front face closer to the axis and in the rotational direction ahead of the rear face, and inclined both radially and circumferentially, ensuring positive pressure in the sealing space across the entire capacity range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the pump operates at capacities higher than the optimal operating point, then the productivity increases, but the pressure in the sealing space drops below the pressure in front of the impeller causing negative pressure that leads to seal damage
Solution Approach 1:
The balancing holes are positioned and angled to preemptively equalize pressures in the sealing space before negative pressure can develop. By arranging the holes with openings on the front face closer to the axis and in the rotational direction ahead of the rear face, liquid is continuously supplied to the sealing space, preventing pressure drop below atmospheric pressure even at high capacities.
Solution Approach 2:
The balancing holes act as an intermediary pathway that allows liquid to flow from the high-pressure front side to the low-pressure rear side of the impeller. This intermediate flow path equalizes pressures across the sealing space, preventing the development of negative pressure that would otherwise damage the seals during high-capacity operation.
2Stress or pressure
If rear vanes are added to pump liquid out of the space behind the impeller, then the pressure in the sealing space decreases, but the device complexity increases and the vanes must be precisely dimensioned for optimal capacity range only
Solution Approach 1:
The invention extracts the pressure balancing function from the complex rear vane system and implements it through simple balancing holes in the impeller shroud. By removing the need for rear vanes and their precise dimensional specifications, the design simplifies the impeller structure while achieving the same pressure control objective across the entire capacity range.
Solution Approach 2:
The invention changes the approach from actively pumping liquid out (rear vanes) to passively allowing liquid flow through (balancing holes). By modifying the hole position, angle, and dimensions, the system achieves pressure balancing without the complexity of moving parts or precisely dimensioned vanes, making the solution effective across all operating conditions.
3Ease of manufacture
If balancing holes are made axial and parallel to the pump axis, then the manufacturing is simplified, but the pressure balancing effectiveness decreases at capacities higher than optimal
Solution Approach 1:
The invention introduces asymmetry in the balancing hole configuration by angling the holes rather than making them axial. The holes are arranged with openings on the front face closer to the axis and in the rotational direction ahead of the rear face, creating an asymmetric flow path that effectively balances pressure across the sealing space at all capacities, including high-capacity operation.
Solution Approach 2:
The invention adds a circumferential dimension to the hole arrangement by angling the balancing holes in the rotational direction. This transforms the simple axial hole into a three-dimensionally oriented passage that leverages both radial and circumferential components, achieving superior pressure balancing effectiveness while remaining manufacturable.
4Stress or pressure
If the pressure in the sealing space drops below atmospheric pressure, then the liquid ring in dynamic seals escapes towards the lower pressure, but air leakage occurs and pumping stops
Solution Approach 1:
The balancing holes provide preliminary counter-action by continuously supplying liquid to the sealing space from the front side, preventing the pressure from dropping below atmospheric pressure. This preemptive pressure equalization stops the liquid ring from escaping and prevents air from flowing into the pump, ensuring continuous pumping operation across all capacities.
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 design maintains positive pressure in the sealing space throughout the pump's capacity range, preventing seal dry-out and air leakage, allowing safe operation at higher capacities without risking seal damage.
Implementation Method 1
liquid from the side of the impeller where the pressure is higher is allowed to be discharged to the area of the lower pressure
Implementation Method 2
liquid is entrained into a space behind the impeller of the centrifugal pump when working vanes of the impeller increase the pressure of the liquid in front of the impeller
Data Source
Figure 1~3
Figure 2
Figure 4
AI summary
The present invention relates to a centrifugal pump and an impeller thereof. The present invention especially relates to modifying an impeller of a centrifugal pump in such a way that said pump may be used without a risk of damaging a shaft seal or like at capacities higher than that at the optimal operating point. A characterizing feature of a centrifugal pump, comprising a pump volute (2), a rear wall (4) of said pump, an impeller (20) having a shroud (22) and balancing holes extending through said shroud, said impeller being attached on the pump shaft (6) and rotating inside said volute (2), is that said balancing holes (26) are arranged through the shroud (22) in such a way that an opening (30) of said holes (26) in the front face of the impeller shroud (22) is both in the rotational direction in ahead of an opening (32) located in the rear face of the impeller shroud (22) and closer to the axis (8) of the pump than the opening (32) in the rear face of the impeller shroud (22).