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FLEXURAL VANE PUMP

Redesigning a rotary vane pump using flexures that has the potential to work in a desalination plant

A rotary vane pump is a positive-displacement pump that uses vanes mounted in a rotating rotor to move the fluid. The vanes move in and out of a channel or cavity in the rotor while maintaining contact with the surrounding stator walls. This contact is crucial as any leakage of the fluid would undermine the pump's functionality. Centrifugal or high pressure vanes are some of the commonly used designs. However, these designs can cause jamming because of its geometry and loads. The goal of this project is to design and evaluate the potential of a flexural vane that would solve these issues by addressing the friction between the vane and the surrounding channel wall.

FLEXURE STRIP
FLEXURE COIL

Review and Redesign

Considering the functional requirements, there were two main concerns with this design. First, since the flexure strips are made from 3D-printed plastic, it does not have the same flexible properties as thin metal flexure strips. Under very little strain, the plastic flexure strips break, limiting the vane’s range of motion. Second, when the vane is printed as one assembly with the main body and the flexure groups, it cannot be placed into the rotor. The four flexure groups are divided into two main chambers: top and bottom. Since these chambers are cut within the rotor and the wall opening of the rotor only has a channel for the vane to travel through, the vane assembly cannot be fixed in the rotor.

 

Future iterations would consider using different materials for the flexure strips such as thin sheets of metal and printing the vane as separate parts that can be fitted into the rotor.
 

After reviewing the printed prototype, there were a few notable considerations. First, the complete assembly of the vane and two coils were not expected to print well compared to the assembly of three separately printed parts. However, the complete assembly proved to be stronger and closer to the desired dimensions. Furthermore, the coils were expected to be much stiffer. However, the resulting low stiffness of the coils allowed for a greater range of motion for the entire vane assembly. The main risks were seen in two areas further shown in the last image:

  1. The tight slot dimensions for the coils did not allow the coils to seamlessly slide in.

  2. The length of the back chamber was too short as the vane was blocked by the back wall when fully compressed.

Future iterations would address these points.

Design Generation

Design 1

The first design is a one-chamber solution that uses a total of eight flexure strips as shown in the images on the right. This solution creates much more robust linear motion, little potential for racking, and larger range of motion. However, it is the most complex design and would, therefore, be more difficult to manufacture, especially as one assembly or print.

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Design 2

​The second design is a two-chamber solution that also uses flexure strips. However, this only uses a total of four strips as shown in the left image. This is a much simpler design that still creates linear motion. However, the flexure strips in this design are subject to both bending as well as stretching and have less range of motion than the first design.

Design 3

The third design achieves linear motion in two ways. First, by constraining the vane in two main areas the vane can move along the channel without significant racking. Second, one assembly of the flexure strips consist of one fixed block and one free block as shown in the figures on the right. There are two different flexure lengths: the length of the flexure strips between the fixed and free blocks and the length of the flexure strips between the free block and the vane. This allows for the vane to achieve a significant range of linear motion within the channel. The dimensions a and b, as shown in the images on the right, will determine the range of motion along the x-axis.

Design 4

The last design is a coil solution as shown in the left image. The coils are attached to the vane at two ends, both contained in two separate chambers. The vane design is also shown in the images on the left. This solution creates stable linear motion, has minimal potential for racking, allows a large range of motion, and keeps the vane in contact with the stator walls without applying too much unnecessary force. The potential risks of this design is that it is moderately complex in design and manufacturability and would most likely not be built or printed as one assembly.

Design Selection

When selecting the final design solution, a few functional requirements were considered. First, it must allow the vane to maintain contact with the stator wall. Second, it must minimize friction both between the vane and the channel as well as between the vane and the stator wall. Third, failure potential must be considered in terms of the stresses that the design experiences. Lastly, the solution must be relatively simple in design and manufacturability.

One design for each type of flexure was chosen. Based on this criteria, Design 3 and 4 were chosen.

CAD Modeling

Autodesk Fusion 360