Rotary-oscillating subassembly and rotary-oscillating volumetric pumping device for volumetrically pumping a fluid

A rotary-oscillating sub-assembly for positive displacement pumping of a fluid, said sub-assembly comprising:

• a hollow body defining a cylindrical cavity of longitudinal axis and having a wall with at least two ducts passing therethrough and opening out radially into said cavity;
• a piston housed in said cavity with which it co-operates to define a working chamber and including, in its cylindrical surface, a kind of longitudinal channel or recess that opens out longitudinally into said working chamber, said piston being provided with a sealing gasket that is made of a material having a modulus of elasticity that is less than the moduli of elasticity of said piston and of said body, and that is carried by said piston, the gasket running beside said channel so as to guarantee leaktight sealing between said piston and said cavity, the piston being movable angularly so as to put said working chamber into fluid-flow communication with at least one, then none, then at least the other of said ducts, and being movable in longitudinal translation to reciprocate so as to cause the volume of said working chamber to vary and successively suck in and then discharge said fluid via one then the other of said ducts, said sub-assembly being characterized in that the piston includes a first axial end remote from a second axial end, said second axial end being in contact with the working chamber;
• said sealing gasket is made up of a plurality of portions comprising:
• a first sealing portion in the shape of a ring that extends around the cylindrical surface of the piston beside its first axial end;
• a second sealing portion in the shape of a half-ring that extends around the cylindrical surface of the piston beside its second axial end, the half-ring having two ends that are spaced apart from each other over the cylindrical periphery of the piston;
• and a third sealing portion that is formed by two sealing strips that extend axially over the outside surface of the piston respectively between a first end of the half-ring and the ring, and between a second end of the half-ring and the ring;
• in that the two strips are angularly distinct from each other and each defines:
• a first sealing line that angularly borders said channel, said first sealing lines being spaced apart from each other by an angle containing said channel, that is greater than each of the angles between the edges of either one of the ducts, and that is less than each of the angles between the adjacent edges of either one of the ducts and of its corresponding duct;
• and a second sealing line, each second sealing line being spaced apart from one of said first sealing lines by an angle that does not contain said channel, that is less than each angle between the edge of one duct and the adjacent edge of its corresponding duct, and that is greater than each angle between the opposite edges of either one of the ducts;
• and in that
• an angle between each first sealing line from at least one of the second sealing lines, and containing said channel, is greater than an angle between the axially-opposite edges of the two ducts.