Pump Impeller Mounting via Differential Thread System
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Solution Overview
Problem
Existing methods for attaching a pump impeller to a drive shaft, such as conical seat attachments, require labor-intensive tools and can lead to damage, especially when the impeller is made of plastic, due to the tight press fit and difficulty in detachment.
Innovation Solution
The implementation of a differential thread system where the shaft has an external thread for a nut with an internal thread, and the nut has an external thread that fits into the impeller's internal thread, with different pitch threads allowing easy detachment without tools by pulling the impeller axially, using a metal impeller bushing to absorb radial forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conical seat attachment method is used to fasten the impeller to the drive shaft, then the impeller can be securely mounted, but the impeller becomes difficult to remove and may be damaged during removal
Solution Approach 1:
The fastening system is segmented into two independent threaded connections: one between the shaft and nut, another between the nut and impeller bushing. This segmentation allows the removal action to be applied through the nut without directly stressing the impeller material, enabling easy removal while maintaining secure mounting.
Solution Approach 2:
The metal impeller bushing acts as an intermediary between the threaded fastening system and the plastic impeller. The bushing absorbs the radial clamping forces and protective function, preventing these forces from directly acting on the plastic impeller which would cause damage during mounting or removal operations.
2Ease of operation
If a puller tool is used to remove the impeller from the drive shaft, then the impeller can be detached, but the process becomes labor-intensive and may damage the impeller
Solution Approach 1:
The differential thread system enables the impeller to be removed without external removal tools. By turning the nut in the loosening direction, the system automatically generates the axial pulling force needed to detach the impeller, making the removal process self-service and eliminating the need for labor-intensive puller tools.
Solution Approach 2:
Instead of using a puller tool to forcibly extract the impeller, the invention inverts the approach by using the fastening nut itself to generate the removal force. The nut, when turned in the loosening direction, pulls the impeller axially relative to the shaft, converting the fastening mechanism into a removal mechanism.
3Strength
If a tight press fit is used between the shaft and impeller, then the connection is secure, but disassembly becomes excessively difficult
Solution Approach 1:
The connection transitions from a static tight press fit to a dynamic threaded connection. The differential thread system allows the connection strength to be adjusted by the tightening torque applied to the nut, while simultaneously providing a controlled mechanism for disassembly by reversing the rotation direction, thus resolving the contradiction between secure mounting and easy disassembly.
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
Enables easy, non-destructive detachment of the impeller from the shaft without a removal tool, with the connection being self-tightening and allowing both assembly and disassembly using the same nut, reducing the risk of damage and simplifying the process.
Implementation Method 1
the thread pair between the shaft end and the nut has a larger or smaller pitch than the pitch of the thread pair between the nut and the impeller opening
Implementation Method 2
Due to the different thread pitches of the two threaded fasteners, tightening the nut causes the impeller to pull axially relative to the shaft
Implementation Method 3
the impeller opening being attached to a correspondingly shaped conical seat of the drive shaft with a conical inner wall
Implementation Method 4
overcome the clamping force on the conical seat
Data Source
Figure 1~2
AI summary
Fixture of a pump impeller wheel (1) in which the coaxially arranged aperture, and where the drive shaft has a conically-shaped inner wall which is fixed on a correspondingly shaped seat of the shaft. The shaft end (10) has an external thread on which a nut (13) is seated with its inner thread, and the nut (13) has an outer thread with which it is seated with an inner thread of the impeller wheel opening. The thread-pair between the shaft end (10) and nut (13) have a greater or smaller pitch than the pitch of the thread pair between the nut and impeller wheel opening.