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Rotary positive displacement machine





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French patent application FR0210959 filed on September 5th, 2002 and entitled “Machine tournante à capsulisme”


André KATZ

Statut commercial

Non-exclusive licenses and collaborative research.


Centre de Physique Théorique de l’École Polytechnique (CPHT, UMR7644), Palaiseau, France



This positive displacement machine is made of two rotors, one inside the other, which rotate at different speeds around parallel axes.
There are sliding contacts between the rotors, and cavities of variable volumes are formed between the consecutive contacts.
The specific feature of the geometry is that each cavity begins and ends with a zero volume. In the positions where these events occur, the two rotors are osculating (the relative curvature is zero) and this has several interesting consequences.
There are two types of this geometry: the external rotor may have one lobe more or less lobe than the internal one.
It may be straight, have a short or long helix with different distribution mechanisms.
The long helix results in geometrically exact instances of the progressive cavity machine (Moineau pump).


With liquids:

  • hydrostatic transmission (pumps and motors)
  • pumping of delicate fluids (as emulsions)
  • pumping of liquids in equilibrium with their vapor, even in the cryogenic field.

With gas:

  • compressors, vacuum pumps and related machines.

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