As you should know this rotor is part of what we call PCP's (Progressive Cavity Pumps) and they are used in several areas in the industry. In my area, oil well drilling, they are part of what we call, drilling motors. Google it!!
The rotor it self has two types of geometries designs:
- Cross-sectional
- Axial
Cross-Sectional
Its cross-sectional design is ruled by the hypocycloid. If the inner rolling circle has diameter ratio of 6:1 related to the outer circle, the rotor will have 6 lobes.
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| Example of a hypocycloid taken from http://images.yourdictionary.com/hypocycloid |
Axial
Its axial geometry is going to look like a helix and can be solely defined by pitch length.
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| A Dyna-Drill drilling motor model inside of its stator. |
I will take an example from the specs inside the following link: http://www.cougards.com/wp-content/uploads/_pdfs/Motor%20Operations%20Handbook%202012.pdf
Usually the manufacturers are not going to release the amount of rubber coverage is inside of a stator. I've never did a motor maintenance ... so, we must "engineering" assume some of the values. In other words, we must guess.
From the specs, comes the following picture
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| Some measurements from a drilling motor |
We want the value related to the rotor's length. It should be "H"-"F". To have a value we must pick one motor. I choose a 8" 7-8 4.0 drilling motor. The power section's length should be approximately 5.8 m. The rotor's I must "engineering" guess that would be 6.5". From the specs we know the pitch in this power section will be 4.0 divided by 5.8m and the rotor will have 7 lobes. We have all the values right now!!
We can begin.
I'll post the solution on the next post.
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