US 3567345 A
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March 2, 1971 PERISTALTI C PUMP Filed Feb. 1o, 1969 United States Patent O 3,567,345 PERISTALTIC PUMP John W. Ballentine, Manhattan Beach, Calif., assignor to W. S. Shamban & Co., West Los Angeles, Calif. Filed Feb. 10, 1969, Ser. No. 798,086 Int. Cl. F 04h 43/00, 43/08 U.S. Cl. 417-477 5 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The invention relates to a peristaltic pump of the type disclosed in the Ballentine et al. Pat. 3,402,673, which disclosure is hereby incorporated into the present disclosure by reference.
In the operation of such a peristaltic pump, successive impeller rollers on a motor-driven rotor traverse a section of resiliently flexible plastic tubing to squeeze the tubing across its width to seal the interior of the tubing at successive traveling points and thereby form successive pump chambers which iirst expand longitudinally while open at their output ends. To squeeze or flatten the tubing, the impeller rollers may press the tubing against a cooperating arcuate wall of the pump or, instead, the section of the tubing may be anchored at its opposite ends against longitudinal slippage to cause the tubing to form a sling and the impeller rollers may flatten the tubing by placing the sling under tension.
A rotor equipped with three impeller rollers severely stresses the tubing at a relatively high frequency that is three times the r.p.m. of the rotor to cause the structure of the tubing to deteriorate at a relatively rapid rate. The consequent short service life of the tubing is expensive in the cost of replacement as well as in the time lost for replacement and in the labor cost involved.
The broad object of the invention is to improved such a peristaltic pump in a manner to substantially increase the service life of the tubing for corresponding reduction in this expense.
SUMMARY OF THE INVENTION It is well known that the number of cycles of stress that a plastic member can withstand before it fails increases as the severity of the stress is reduced and that the rate of increase is exponential. Thus if a given stress just suicient to cause immediate failure of the plastic is reduced to 75%, the plastic will survive a few cycles; if the stress is reduced 50%, the plastic will survive over one thousand cycles; reduction of the stress from 50% to 40% increases the number of cycles to a hundred thousand and below 40% the curve attens out to such an extent that when the stress is reduced to approximately 25% the service life of the plastic is increased indefinitely. Heretofore it has been regarded as impossible to take advantage of this fact because of the logical assumption that failure to flatten the plastic tubing to the usual drastic degree would cause the efficiency of the pump to drop otf in the same exponential manner and in addition would eliminate the self-priming capability of the pump.
Repeated testing of the life of a whole series of plastic tubes in peristaltic pumps reveals that the tubing fails at the two opposite longitudinal side edges of the attened tubing where the tubing wall is folded to a sharp ICC band. The present invention is based on the discovery that the degree to which the tubing is flattened in these two critical zones can be reduced substantially without significant sacrilice of the pump el'liciency. Accordingly, the invention teaches flattening the tubing by the impeller rollers to the usual degree only along a wide central longitudinal zone of the tubing, each of the two longitudinal edge portions of the flattened tubing being permitted to bulge to permit the 180 folds to assume a liberal radii of curvature.
An important advantage of carrying out this concept is that the reduction in the stressing of the tubing wall greatly lessens the generation of heat in the tubing material, which reduction in heat in itself not only conserves the tubing but also reduces the possibility of the flattened walls of the tubing being welded together under the pressure of the impelled rollers. The lessening of the likelihood of welding the two walls together makes it possible to flatten the central longitudinal zone of the tubing to greater than the usual degree.
In one embodiment of the invention, each of the impeller rollers is improved by providing the roller with two circumferential grooves that are spaced yapart to register with the two longitudinal edge portions respectively of the flattened tube. The two grooves are of a dimension and of a cross-sectional curvature to permit the two longitudinal edges of the flattened tubing to bulge to a radius of curvature to reduce the stressing of the material to the desired degree without significantly sacrificing the efciency of the pump. The two circumferential grooves of an impeller roller serve the further purpose of tracking the tubing in that the two grooves cooperate with the budged edge portions to tend to maintain the tubing in alignment with the impeller roller.
In a second embodiment of the invention, each of the impeller rollers is only wide enough to flatten the desired central longitudinal zone of the tubing, the relatively narrow width of the roller permitting the two longitudinal ledges of the flattened tube to bulge to the desired degree. In this second embodiment of the invention, the tracking function may be carried out by providing the relatively narrow impeller roller with hub extensions on its opposite ends and by mounting disks on the two hub portions respectively to confine the tubing in alignment With the impeller rollers.
The various features and advantages of the invention may be understood from the following detailed description and the accompanying drawings:
BRIEF IDESCRIPTION OF THE DRAWINGS In the drawings, which are to be regarded as merely illustrative:
FIG. 1 is a perspective view of the peristaltic pump incorporating the presently preferred embodiment of the invention;
FIG. 2 is a view of an impeller roller of the pump shown in FIG. l, the view being partly in section and partly in side elevation and showing how the impeller roller permits bulging of the opposite longitudinal edges of the flattened tubing;
FIG. 3 is a similar sectional view of a second embodiment of an impeller roller; and
FIG. 4 is a graph showing how the service life of a plastic member is increased by reducing the degree to which the member is cyclically stressed.
DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION FIG. 1 shows a peristaltic pump mounted on a base plate 10 wherein a motor 12 provided with reduction gearing in a gear case 14 drives a rotor 15 that is provided with three impeller rollers 16 on three corresponding spindles 18. The three impeller rollers 16 successively traverse a section of tubing 20 adjacent a concentrically curved wall 22 of the pump structure that terminates in two outwardly turned wings 24. The tubing 20 is anchored against longitudinal slippage by two corresponding clamp plates 2S that straddle the tubing and clamp the tubing against the two wings 24 respectively. For adjustment each of the two clamp plates 25 is formed with a longitudinal slot 20 that receives a corresponding fixed screw 28, the screw carrying a suitable thumb nut 30.
The arrangement may be such that the impeller rollers 16 successively flatten the tubing 20 by pressing the tubing against the arcuate wall 22. If desired, however, the tubing may be formed into a sling between the two clamp plates 25 with the sling dimensioned relative to the orbit of the impeller rollers to be placed under tension by each roller in turn to such degree as to flatten the tubing to the desired extent.
In accord with the teaching of the invention, each of the impeller rollers 16 is so shaped and dimensioned as to flatten only the major portion of the width of the tubing along a central longitudinal zone of the tubing and to permit the two longitudinal edges of the flattened tubing to bulge to the desired degree. For this purpose each of the impeller rollers in the pump of FIG. 1 is formed with two circumferential grooves 32 near its opposite ends as best shown in FIG. 2, the two grooves being dimensioned and spaced to register with the two longitudinal edges of the flattened tube and to permit the longitudinal edges of the flattened tube to bulge as indicated at 314. In IFIG. 2 the impeller roller 16 compresses the tubing 20 against the surface of the arcuate wall 22 but, as heretofore stated, the impeller roller need not cooperate with the arcuate wall in this manner.
The main body portion 35 of the impeller roller 16 that is bounded by the two circumferential grooves 32 is of uniform diameter but tapers at its opposite ends into the two grooves. The main body portion 35 is narrow enough to permit the bulging of the opposite longitudinal edges of the tubing and with the two circumferential grooves 32 registering with the bulged edge portions 34 of the flattened tubing, the two circumferential grooves tend to track the tubing in the sense of confining the opposite longitudinal edges of the flattened tubing and thus tend to maintain the tubing in alignment with the impeller roller.
`Because the opposite longitudinal edge portions of the flattened tubing are permitted to bulge in the manner described, small voids 36 are formed by the small radii of curvature inside each of the two 180 folds of the tubing wall at the opposite longitudinal edges of the fiattened tubing but, surprisingly, these voids do not cause the efficiency of the pump to drop to a significant extent. In any event, the degree to which the life of the tubing is extended is of importance far exceeding the importance of any loss in efficiency of the pump if the impeller rollers are appropriately shaped and dimensioned within the expected skill in this art.
The graph shown in FIG. 4 is taken from Fundamentals of Plastics by Richardson and Wilson. The graph shows how, as previously explained, the life of the plastic member increases exponentially as the relative stress of the plastic member is progressively reduced. In continuous highly accelerated tests carried out twentyfour hours a day, sections of plastic tubing acted upon by conventional impeller rollers to create a pump discharge at 13 p.s.i. were found to survive approximately one week. Substitution of impeller rollers of the new configuration disclosed herein resulted in extending the life of the tubing to thirty days. In practice the service life of a section of tubing is increased at least three fold.
FIG. 3 shows a second embodiment of an impeller roller, designated 16a, wherein the full width of the roller is substantially the same as the width of the body portion 35 of the rst described impeller roller. The impeller 4 roller 16a is of uniform diameter but is tapered with rounded edges at its opposite ends to permit the opposite longitudinal edge portions of the flattened tubing to bulge with the desired curvature.
For the purpose of tracking the flattened plastic tubing, each impeller roller 16a is provided with hubs 40 at its opposite ends on which are mounted corresponding disks or flanges 42 that overhang the opposite longitudinal edges of the flattened tubing to confine the flattened tubing and thus maintain the flattened tubing in correct alignment with the impeller roller. It is to be noted that the hubs 40 provide adequate clearance for bulging of the opposite edge portions of the flattened tubing. The disks 42 may be fixed relative to the impeller roller 16a or may be free to rotate to minimize relative movement between the disks and the edges of the flattened tubing.
My description in specific detail of the selected embodiments of the invention will suggest to those skilled in the art various changes, substitutions and other departures from my disclosure.
What is claimed is:
1. In a peristaltic pump wherein impeller rollers on a rotor successively traverse a section of resiliently flexible tubing in a compressive manner to cause fluid in the tubing to travel lengthwise of the tubing, the improvement comprising:
each of said impeller rollers being of an axial dimension substantially less than the width of the tubing when the tubing is fully flattened, each of said rollers 'being positioned centrally of the width of the flattened tubing to flatten a central longitudinal portion of the tubing with the opposite longitudinal edge portions of the flattened tubing free to bulge to avoid damaging stressing of the opposite longitudinal edge portions;
each of said impeller rollers being provided with hubs at each of its opposite ends of substantially smaller diameter than the roller to clear the opposite bulged edge portions of the tubing; and
two disks rigidly mounted on the respective hubs to block sidewise movement of the tubing out of alignment with the roller and to maintain the tubing in alignment with the roller.
2. In a peristaltic pump, the combination of:
fixed structure having an arcuate concave surface;
a section of resiliently flexible tubing extending along said arcuate concave surface,
the width of said concave surface exceeding the width of the tubing when the tubing is flattened; and
a rotor within the region defined by said concave surface;
a plurality of rotary means journalled on said rotor and movable thereby adjacent said concave surface to flatten the tubing against the concave surface,
each of said rotary means having a central cylindrical portion of uniform diameter of less width than the width of the flattened tubing and centered relative to the flattened tubing with opposite longitudinal marginal portions of the flattened tubing extending beyond said cylindrical portion,
each of said rotary means having portions on opposite sides of said cylindrical portion overlying said marginal portions of the flattened tubing, said overlying portions of the rotary means being reduced portions of less diameter than said central cylindrical portion to permit said marginal portions of the tubing to bulge away from the concave surface towards the rotary means,
said rotary means having two opposite side portions overhanging the outer sides of said longitudinal marginal portions of the flattened tubing to keep the flattened tubing centered relative to the rotary means.
3. A combination as set forth in claim 2 in which said rotary means comprises a roller of greater axial dimension than the width of the attened tubing,
said roller having two circumferential grooves positioned to register respectively with said longitudinal marginal portions of the flattened tubing.
4. A combination as set forth in claim 2 in which the rotary means comprises a central roller of less width than the flattened tube and two radial flanges rotatable with said roller and spaced from the opposite ends respectively of the roller to clear said longitudinal marginal portions of the tubing,
said flanges being of greater diameter than the central roller and straddling the attened tubing to keep the flattened tubing centralized relative to the central roller.
5. A combination as set forth in claim 4 in which the two opposite ends of said central roller are rounded in prole.
References Cited UNITED STATES PATENTS 3,402,673 9/1968 Ballentine et al. 103-149 3,122,103 2/1964 Ormsby 103-149 2,434,802 1/1948 Jacobs 103-149 1,765,360 6/1930 Baumann 103-149 2,987,004 6/1961 Murray 103-149 FOREIGN PATENTS 1,380,460 10/1964 France 103-149 851,331 1/1959 Great Britain 103-149 HENRY F. RADUAZO, Primary Examiner