PERISTALTIC PUMP ADAPTED TO OPERATE SIMULTANEOUSLY ON TWO LINES

Abstract: Peristaltic pump adapted to operate simultaneously on two lines (5, 6) having a rotatable head (1) provided with rollers (2, 3, 4) housed within a fixed body (8), having an internal cylindrical wall defining at least one first (7a) and at least one second (7b) arcuate surface so that the rollers (2, 3, 4) of the rotatable head (1) define a first interspace, comprised between the first arcuate surface (7a) and the perimetral surface of at least one roller (2, 3, 4) defining, in cross-section, a thickness which is greater than the thickness of the section of the second interspace defined by the second arcuate surface (7b) and the same roller (2, 3, 4).

Description: The invention relates to a peristaltic pump adapted to operate simultaneously on two lines. As known, peristaltic pumps comprise a rotatable head provided with rollers adapted to compress at least one fluid conveyance line or pipe made of flexible or soft material, such as, for example, PVC, silicon, or polyurethane, against portions of cylindrical resting surfaces for said line provided in the fixed body of the pump. An essential condition for good operation of the pump is that the rollers exert against at least one line such a pressure as to provide the perfect occlusion of said line, and for this purpose the pumps are provided with micrometric adjustment means or with self-occlusive spring systems. DE-A-2 162 998 discloses a peristaltic pump comprising a cylindrical rotor having presser rollers arranged on its periphery which engage, upon rotation of the rotor, with a flexible fluid conveyance line. The conveyance line is accommodated in a housing element which is linearly movable, away from and towards the center of rotation of the rotor, by appropriate mechanisms, and thereby the pressure of the rollers on the conveyance line can be varied. FR-A-2 388 255 shows a peristaltic pump which includes a pair of opposing jaw members which are each pivotable about respective diametrically opposite axes. The jaws are provided with substantially semicircular walls which form a substantially cylindrical accommodation seat for a cylindrical rotor provided peripherally with a plurality presser rollers. A pair of identical flexible tubes are easily arrangeable, due to the pivoting of the jaws, each at the respective semicircular walls of the jaws in order to be engaged by the rotating presser rollers. CH-A-463 284 shows a linearly actuated presser roller which occludes a series of flexible conveyance lines arranged in a plane against a supporting body. The supporting body has a step-like configuration at its side facing the conveyance lines, and thereby the individual conveyance lines can have different diameters while being pressed by the same roller. Typically, use is made of these pumps in the medical field, for example for infusing drugs, or in extracorporeal blood circuits. It often occurs that a peristaltic pump has to operate simultaneously on two lines which must convey different flows of fluid in a precisely determined ratio, as required for example in the case of the simultaneous conveyance of blood in one line and of anticoagulant liquid in the other, and the required ratio between the flow rates of the two fluids is achieved by means of an appropriate choice of the passage areas of said lines. In this type of situation however, an operator having a known type of peristaltic pump available encounters serious limitations: in known pumps, in fact, the two portions of cylindrical resting surfaces of the two lines have the same radius of curvature and therefore it is necessary to employ lines with different passage areas but having the same wall thickness if it is desired to comply with the condition that the rollers, in making contact with said lines, achieve such a compression thereof as to obtain their perfect occlusion. The provision of such lines is always difficult, and it is thus an aim of the present invention to provide a peristaltic pump which is adapted to efficiently operate simultaneously on two lines, without requiring that the two lines necessarily have the same wall thickness. The proposed aim is achieved by a peristaltic pump adapted to operate simultaneously on two lines, as defined in the appended claims. Further features and advantages of the invention will become apparent from the description of a preferred but not exclusive embodiment thereof, shown in the accompanying illustrative, non-limitative drawings, wherein: figure 1 is a sectional schematic plan view of the pump, taken along the line I-I of fig. 2; figure 2 is a front elevation view of the pump according to the invention; With reference to the above described figures, the peristaltic pump comprises a rotatable head 1, rotatable within a substantially hollow cylindrical fixed body 8 which, is provided with two semi-cylindrical internal surfaces each having a first arcuate or curved surface 7a and a second arcuate or curved surface 7b arranged coaxially with respect to the rotation axis 11 of the rotatable head 1, and being provided with openings 9 and 10. With reference to figure 2, the body 8 is supported on a fixed supporting ring 15 having a bevelled peripheral edge 16 wherewith a complementary bevelled edge 17 of the sleeve-like body 8 is engaged and centered by virtue of the mating conical surfaces 16 and 17. The body 8 is covered by a removable lid 20 and is fixed on the ring 15 by catch mechanisms, not illustrated in the drawing figures. The supporting ring 15 is fixed on a base plate 18 having an aperture 19 wherethrough the transmission assembly 13 extends internally of the body 8. The rotatable head 1 is upwardly keyed to the shaft 12 of the transmission assembly 13, schematically illustrated in Figure 1, such that rotation of the shaft 12 transmits rotational movement to the rotatable head from a motor, which is not shown in the drawing figures. According to another embodiment, instead of the gearwheel transmission assembly 13, the shaft 12 may be rotatably driven by a suitable electric motor, also not shown in the drawing figures. The rotatable head 1 furthermore comprises rollers 2, 3, 4, rotatably associated with pins 2a, 3a, and 4a through anti-friction means, within hollow seats provided in the body of the head 1 proximate to a peripheral surface thereof, only the pin 4a and the roller 4, wherein a bearing 4b is visible, are schematically illustrated in figure 2. More precisely, the axes of the pins 2a, 3a and 4a are parallel to the rotation axis 11 of the rotatable head 1. Advantageously, the rollers have a portion protruding from the peripheral surface of the rotatable head so as to interact with the flexible tubes or lines 5, 6 in a per se known manner as described e.g., in the published German Patent No. 2,162,998. Positioning stud-like elements 9a, 9b and 10a, 10b are provided proximate to each opening 9 and 10, respectively, and have the function of aligning the lines 5 and 6, which are arranged between the surfaces 7a and 7b of the fixed body 8 and the surface of the protruding portions of the various rollers 2, 3, and 4. The lines 5 and 6 are constituted by flexible tubes, made for example of a plastic material, and in the instant case having different external diameters. The rollers 2, 3, and 4 define, during rotation of the rotatable head 1, a first interspace comprised between the first curved surface 7a and the perimetral surface of each roller, and a second interspace comprised between the second curved surface 7b and the perimetral surface of the rollers 2, 3, and 4. Advantageously, the first interspace has a cross-sectional thickness which is smaller than the cross-sectional thickness of the second interspace. In particular, the surface 7a has a radius of curvature r which, when referred to the rotation axis of the rotatable head 1, is smaller than the analogous radius of curvature R of the curved surface 7b. In this manner the interspace between the surface 7a and one of the rollers 2, 3 or 4, is smaller than the interspace between the surface 7b and said rollers 2,3 or 4. Thus, the flexible tube 5 of smaller diameter is positioned at the surface 7a of smaller radius r while the flexible tube 6 of greater diameter is positioned at the wall 7b with greater radius R. More precisely, from the foregoing it will be appreciated that the rollers 2, 3, and 4 describe a circumference which is coaxial to the rotation axis 11 of the rotatable head 1 during rotation thereof. For the sake of clarity, it should be noted that the difference between the radius r of the surface 7a and the distance of the peripheral surface of the rollers 2, 3, and 4 from the rotation axis 11 must be appropriate; that is, in certain conditions slightly smaller than twice the wall thickness of the tube 5; analogous considerations must be applied for the surface 7b and the tube 6. Advantageously, a plurality of fixed bodies 8 may be provided, having internal surfaces 7a or 7b defining radii R and r, which differ with respect to each other and the relative rotatable heads 1 so as to be able to employ flexible tubes with different cross sections in various combinations. As may be noted in Figure 1, the openings 9 and 10 are provided in the form of a missing portion formed in the peripheral wall of the cylindrical body 8. This allows, on one hand, easy inspection during operation of the pump and, on the other hand, removal of the body 8 is extremely facilitated when body 8 of one size should be replaced by a body 8 of another size. As mentioned heretofore, the sleeve-like body 8 is easily removed by an axial displacement and is easily centered by virtue of the conical surfaces 16, 17. In practice it has been observed that the pump achieves the intended aim since it allows to operate on two lines, or flexible tubes, with different cross sections and therefore with different flow rates without the tubes requiring identical wall thicknesses and without complicated adjustments of the pump. The peristaltic pump thus conceived is susceptible to numerous modifications and variations, all within the scope of the inventive concept; furthermore all the details may be replaced with technically equivalent elements. In practice, the materials employed, as well as the dimensions, may be any according to the requirements and the state of the art. Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims: A peristaltic pump adapted to operate simultaneously on two lines (5, 6), comprising a fixed hollow body (8) having at least one cylindrical wall defining at least one first arcuate surface (7a) and at least one second arcuate surface (7b), said first and second surfaces (7a, 7b) being arranged in diametrically opposite positions, said pump further comprising a rotatable head (1) having a peripheral surface and being adapted for rotating with respect to said first and second arcuate surfaces (7a, 7b) coaxially within said hollow body (8), said rotatable head (1) having at least one roller (2, 3, 4), rotatably associated therewith proximate to said peripheral surface and being rotatable about an axis (2a, 3a, 4a) substantially parallel to said rotation axis (11) of said rotatable head (1), said at least one roller (2, 3, 4) having a portion thereof projecting from said peripheral surface to define first and second interspaces between its perimetral surface and said first (7a) and second (7b) arcuate surfaces, respectively, for compressing lines (5, 6) arranged respectively in said first and second interspaces during rotation of said rotatable head (1), characterized in that said first interspace defined by said first arcuate surface (7a) and said at least one roller (2, 3, 4) has a radial width smaller than that of said second interspace defined by said second arcuate surface (7b) and said at least one roller (2, 3, 4). Peristaltic pump according to claim 1, characterized in that the radial distance of said first surface (7a) from said rotation axis (11) of said rotatable head (1) is less than the radial distance of said second surface (7b) from said rotation axis (11). Peristaltic pump according to claim 1, characterized in that said fixed body (8) has a sleeve-like conformation having a bevelled peripheral edge (16) in engagement with a bevelled edge (17) of a supporting ring (15) for said sleeve (8).

Inventors: CALARI, ALESSANDRO
Applicants: DIDECO S.R.L.
Application year: 1989
Main classification: F04B43
IPC codes: F04B43, F04C5