Eccentric Piston Pump Shaft Flexure for Leak Control Under Load
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Solution Overview
Problem
Volumetric eccentric piston pumps experience leaks between the piston and cylinder under load due to pressure-induced deflection of the drive shaft, degrading pump performance.
Innovation Solution
The use of radial springs with an angular offset and a thinned, flexible section of the drive shaft to maintain piston-cylinder contact, ensuring the direction of the restoring force aligns with the contact points, even under load, eliminating the need for radial springs and enhancing piston re-centering efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the drive shaft is made rigid to maintain structural strength, then the shaft can support high pressure, but the shaft deflects under pressure causing piston detachment and leaks
Solution Approach 1:
The drive shaft incorporates a flexible portion with reduced cross-sectional area that allows controlled elastic deformation under pressure. This dynamic flexibility enables the shaft to bend slightly under load, maintaining piston contact with the cylinder wall while still supporting high operating pressures, thereby resolving the contradiction between structural strength and reliable contact.
Solution Approach 2:
The cross-sectional area of the drive shaft is varied along its length, with a specific portion having a reduced area to create flexibility. This parameter change allows the shaft to exhibit different mechanical properties in different sections - rigid in most areas for strength, and flexible in the reduced-area portion for maintaining contact under pressure.
2Reliability
If radial springs are used to press the piston against the cylinder, then piston-cylinder contact is maintained, but the spring force direction becomes misaligned under load causing ineffective pressing
Solution Approach 1:
The radial spring is positioned at an angle relative to the drive shaft axis, and the shaft's flexible portion dynamically adjusts the spring's orientation as the shaft bends under pressure. This dynamic repositioning ensures that the spring force remains aligned with the piston-cylinder contact points throughout the pressure cycle, maintaining effective pressing force.
Solution Approach 2:
The flexible portion of the drive shaft acts as an intermediary between the radial spring and the piston. It transmits and redirects the spring force, adjusting the force direction to remain aligned with the contact points even as the shaft deflects under pressure, thereby maintaining effective piston pressing.
3Reliability
If the drive shaft is made flexible to maintain piston contact, then leaks are reduced, but the shaft may lack sufficient structural strength to support high pressure
Solution Approach 1:
The drive shaft is segmented into distinct portions: a rigid portion with full cross-sectional area for structural strength and pressure support, and a flexible portion with reduced cross-sectional area for maintaining piston contact. This segmentation allows each section to perform its specialized function optimally.
Solution Approach 2:
Different portions of the drive shaft have different mechanical properties - the majority of the shaft maintains full structural strength with standard cross-section, while only a specific localized portion has reduced area for flexibility. This local quality differentiation ensures overall strength is preserved while providing targeted flexibility where needed.
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 reduces leaks and maintains effective fluid blocking between the piston and cylinder, improving pump performance and efficiency by ensuring consistent piston alignment and reducing frictional losses during operation.
Implementation Method 1
the elastic means comprise at least one radial spring mounted at the end of the piston
Implementation Method 2
the direction of the return force of the spring forms a non-zero angle with a straight line passing through the two points of contact between the piston and the cylinder when the pump is empty
Implementation Method 3
the elastic means comprise a first portion of the drive shaft, the surface of the section of which is smaller than the surfaces of the sections of the adjacent portions so as to be able to deform elastically during rotation of the drive shaft
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
The invention relates to a positive displacement pump (1) with an eccentric piston comprising: - a tube (2) having a first end (21) and a second end (22) terminating in a cylinder (24) integral with a discharge zone (4), the tube (2) comprising a suction opening (23) and a discharge opening (41), - a drive shaft (5) extending between the transmission zone 3 and the tube, - a piston (6) arranged in the discharge zone (4) and mounted to slide at the end (53) of the shaft (5) being pressed against the cylinder (24) by elastic means (7) so as to block a displacement of fluid between the tube (2) and the discharge zone (4) when the pump is unloaded, characterized in that the elastic means are arranged to press the piston against the cylinder when the pump is operating under load.