This invention relates to peristaltic pumps, and is particularly concerned with providing an improved peristaltic pump in which pulsatility is substantially reduced.
The necessities of having positive displacement of fluids, uninterrupted flow, little or no pulsatility and good linearity of delivery are usually seen as mutually exclusive criteria for pump design. The linear but cyclic delivery of a syringe-type pump or the pulsatile but continuous output of gear or vane pumps require unacceptable compromises for some applications, especially when complex and expensive pump types are precluded. Additional requirements of zero leak-through, ease of manufacture, low maintenance, low cost and precise delivery rates place additional burdens on design approach.
Peristaltic pumps arc usually simple in construction, have intrinsic valving and little or no leak-through, require low driving forces, provide positive delivery, have uninterrupted fluid paths, and are also suitable for pumping aggressive fluids. However, conventional peristaltic pumps generally suffer from pulsatility and chaotic delivery rates. It is therefore desirable to provide a peristaltic pump in which at least some of the disadvantages of non-linear peristaltic pumps are alleviated.
It is also desirable to provide a linearised peristaltic pump that is inexpensive and simple to manufacture and assemble.
It is also desirable to provide a positive displacement peristaltic pump that has negligible pulsatility and which can provide a consistent delivery of fluid.
According to one aspect of the invention there is provided a linearised peristaltic pump comprising a pump housing, a tube within the pump housing, and tube-engaging means adapted to engage with the tube to pump fluid from an inlet end of the tube to an outlet end of the tube, wherein the tube is clamped longitudinally within the housing in such a manner as to reduce the internal cross-sectional area of the tube.
Preferably, the tube is clamped longitudinally by clamping means over part of its transverse dimension so as to have a substantially flattened clamped part and a bulbous unclamped part. In its clamped condition the cross-sectional shape of the tube generally resembles a letter xe2x80x9cPxe2x80x9d. The tube engaging-means is arranged to engage and compress the bulbous unclamped part of the tube to pump fluid along the tube. By clamping the tube longitudinally in this manner, all but the desired deformations of the tube required for pumping are substantially eliminated removing one of the major sources of non-linearity in peristaltic pumps.
The tube-engaging means may take any convenient form which is arranged to engage and compress the tube progressively between its inlet end and outlet end. Conveniently, the tube-engaging means comprises a plurality of tube-engaging members, preferably in the form of rollers, movable within the housing relative to the clamped tube. The tube-engaging members are preferably arranged to engage and compress the tube during only part of its length between its inlet and outlet ends. The tube is preferably engaged progressively by the tube engaging members in a first tube-encountering sector, fully compressed in a second, fluid-displacing sector in which the lumen of the tube is completely closed, and then allowed to relax progressively in a third, tube-releasing sector to resume its uncompressed, clamped cross-section. This controlled encounter and release of the tube reduces the fluid-displacing volume of the pump but has the advantage of reducing flow variations and pulsatility to negligible levels.
Preferably, the fluid-displacing sector is of substantially equal size to the tube-encountering and tube releasing sectors.
In a particularly preferred embodiment, a plurality of tube-engaging rollers compress the tube during the fluid-displacing sector and are movable on a cam track during the first, tube-encountering and third, tube-releasing sectors so that the compression of the tube is altered progressively as the rollers move within the first and third sectors.
According to another aspect of the invention there is provided a linearised peristaltic pump comprising a pump housing, a tube located within the housing, and a plurality of tube-engaging rollers engageable with the tube to compress the tube to pump fluid from an inlet end of the tube to an outlet end of the tube, wherein the rollers are movable on a single cam track having a single tube-encountering sector in which the compression of the tube is increased progressively to alter the cross-sectional area of the tube in a linear manner, a single fluid-displacing sector in which the tube is fully compressed, and a single tube-releasing sector in which the compression of the tube is decreased progressively to alter the cross-sectional area of the tube in a linear manner, wherein the tube-encountering and tube-releasing sectors of the cam track are of substantially the same length to achieve a substantially linear and pulseless fluid delivery.
A linear peristaltic pump having a substantially straight tube may be provided in accordance with the invention, but preferably the linearised peristaltic pump is a rotary pump having a tube which occupies a substantially circular path within the pump housing, the tube being engageable by a plurality of tube-engaging members rotatable within the pump housing. The tube may be conveniently clamped between a clamping member and a wall of the housing. Preferably, the tube-engaging members comprise rollers which are mounted on the ends of arms connected to a rotary member rotatable about the central axis of the housing. The rollers are preferably spring urged in a radially outwards direction into contact with the cam track during the tube-encountering, fluid-displacing and tube-releasing sectors. A pump of this construction is simple and relatively inexpensive to manufacture and assemble and can provide a consistent delivery with negligible pulsatility.
In a preferred embodiment, the tube is fully compressed in the fluid-displacing sector which occupies approximately one third of the circumference of the substantially circular arc of the tube.