GB2487040A - A linear peristaltic pump - Google Patents

Abstract

A pump with an elongated pump chamber 1 with inlet 2 and outlet 3 ports using a diaphragm 5, flexed in a wave-like manner upon a rigid body 4 to generate peristaltic fluid flow between the inlet and outlet ports. The movement of the diaphragm is controlled externally by means of studs 19 acting in a sinusoidal sequence, where shoes 20 driven by actuators that are attached to the studs tilt as they reciprocate. The diaphragm may be flexed in a manner that maintains suction, prevents back flow and pressurises the discharge and the operation may be reversible. The diaphragm may be reinforced using woven cloth and be made of a wide range of elastomeric materials and the rigid body may comprise a sheet metal stamping. The studs may act to compress and lift the diaphragm.

Description

PUMP

The present invention relates to a pump.

Many types of pump exist, including peristaltic pumps. These have a deformable pump chamber, which can be closed off at a point movable along the chamber. Once the closure point has moved to the outlet end of the chamber, a fresh closure can be made at the inlet end so that the chamber is always closed against return flow and movement of the closure points along the chamber provides corresponding flow * through the pump.

Peristaltic pumps have the advantage of simplicity in that there are no separate valves required between inlet and outlet. Further, they can be arranged for their closure points to be completely opened so that they can be flushed through for cleaning or sterilizing, as in food and pharmaceutical industry uses. They can also pump in a reverse direction.

A disadvantage of peristaltic pumps is the requirement for the pump chamber, usually in the form of a tube, to return to its initial cross-sectional shape to thaw fluid to be pumped into the chamber. Various problems can be involved with this: * i) speed of shape recovery, ii) hysteresis energy losses due to construction of the tube in a form suitable for recovery, iii) expense of such a tube.

The object of my present invention is to provide an improved peristaltic pump.

My improvement is the provision of a means for positively restoring a peristaltic pump tube to its cross-sectional shape prior to closure deformation.

A peristaltic pump according to my invention comprises: A deformable pump chamber, which is laterally closable sequentially along its length; wherein: the pump is adapted for positive opening of the chamber sequentially along its length after its closure.

It is within the scope of my invention that the pump chamber should be comprised of a fully flexible wall. However, at least in the embodiment, which I prefer, the chamber is bi-lateral that is having a flexible wall-or diaphragm -to one side and * having a rigid wall on an opposite side. Typically the diaphragm will be of elastomeric material with longitudinal and lateral reinforcement.

Whilst normally the chamber will be open by mechanical connection of the deformation means to a deformable part of it, I can envisage that the chamber may be opened by non-mechanical means. For instance, where the chamber comprises a rigid wall opposite a diaphragm, the diaphragm may be drawn up by vacuum for its positive opening after sequential closure by the deformation means. The latter may be contained entirely within an evacuable space divided from the pump chamber by the diaphragm or the deformation means may have actuating components extending into the space via seals.

For mechanical connection of the flexible wall -usually the diaphragm -it may be provided with a continuous connecting member along its length. For instance, this may be a flexible rail of extruded material, such as nylon, polypropylene or titanium.

However I prefer a series of discrete connection members such as metal studs. The head of the stud may have circular or rectilinear form to maximise elastomeric bonding.

For sealing of the diaphragm to the opposite wall, a series of shoes are preferably provided with a shape complementary to the shape of the opposite wall, allowing for the thickness of the diaphragm and a preferred small compression of the diaphragm.

The shoes can be shaped on their diaphragm side in cross-section parallel to the length of the diaphragm. Preferably this shaping provides both a line contact across the diaphragm for sealing of it to the opposite wall and ability to rock with respect to the opposite wall.

Where mechanical connection is provided between the deformation means and the diaphragm, an actuator will usually be provided for each diaphragm shoe. The actuator may be desmadromic or may rely on spring return for positive opening of the chamber after its sequential closure. Where spring return is used, a variety of * conventional mechanical drives can be used, particularly of the cam and follower nature. A series of cam followers connected to the shoes and the studs can be arranged to be depressed by a cam, which may be one or more roller or slide element(s) circulated on a chain past the followers. Alternatively, the followers may be acted on by a series of cam lobes arranged on a shaft extending along the length of the diaphragm. Again, the series of cam lobes may be replaced by a continuous spiral cam. Another feature of my invention is that when the pump is at rest i.e., not pumping, it also acts as a stop valve. The operating strain on the diaphragm can be reduced if, either or both; leading and final shoes have a reduced operating stroke.

This is typically 50% of the stroke of the other shoes and is sequenced in harmony with each shoe adjacent to a full-stroking shoe.

It should be noted that although I refer above to the longitudinal direction of the pump chamber, I do not mean to limit it to being of rectilinear configuration. For instance the chamber may be arranged to be toroidal with a break where an inlet and outlet are adjacent each other. For this arrangement, a cam element mounted radially of a shaft central to the pump chamber is particularly suitable. The actuating cam followers can act radially or longitudinally of the shaft according to whether the diaphragm is arranged to face inwardly or outwardly of the toroid or axially about it.

Desmadromic drive may be provided by conventional mechanical actuation arrangements such as a crankshaft with a respective throw and connecting rod for each diaphragm shoe. Alternatively, a shaft with an eccentric and scotch yoke for each shoe may be provided. In a different arrangement, a pneumatic or hydraulic actuator, preferably under electronic control, can be provided for each shoe. I anticipate that such actuators would be particularly suitable for larger pumps.

To help understanding of my invention, specific embodiments of it will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic, longitudinal cross-sectional view of a pump of the invention, Figure 2 is a transverse cross-sectional view of the pump of Figure 1 at one diaphragm-actuating shoe, with the shoe withdrawn, Figure 3 is a scrap view of certain of the shoes shown in Figure 1, Figure 4 is a view similar to Figure 2 with the shoe advanced for compression of the diaphragm against the opposite wall, Figure 5 is a view similar to Figure 3 showing the sequence of advance of the shoes, Figure 6 is a view similar to Figure 2 of a cam-operated actuator, Figure 7 is a view similar to Figure 6 of a scotch yoke operated actuator, Figure 8 is a view similar to Figure 1 of spiral cam actuated pump, Figure 9 is a similar view of an electro-hydraulically operated pump, Figures 10 & 11 are diagrammatic plans and cross-sectional views of a toroidally arranged pump of the invention, Figure 12 is a side view of another pump of the invention, Figure 13 is a cross-sectional view showing the diaphragm in open and shut positions, Figure 14 is a similar view to Figure 13 of a peristaltic tube or hose, Figure 15 is a cross-sectional view showing a coupling between a shoe and oscillating thrusting mechanism, Figure 16 shows an alternative toroidal pumping arrangement, Figure 17 is a schematic plan showing a multiplicity of diaphragms, Figure 18 is a schematic plan showing an irregular arrangement of actuating shoes Figure 19 is a longitudinal cross-sectional view showing the diaphragm being flexed by non-mechanical means.

Figure 20 is a cross-sectional view showing a spring and a shoe and diaphragm being prevented from sealing against the pump body because of obstructions.

Figure 21 is a section through a stem showing how a spring unit can be used to accommodate an obstruction preventing the diaphragm from sealing against the pump body.

Figure 22 shows a half-cross-section of the assembled diaphragm cover, diaphragm * and pump body.

Figure 23 shows the components in Figure 22 prior to final assembly.

Referring first to Figure 1, the pump there shown has an elongated pump chamber 1 extending between an inlet 2 and an outlet 3. The chamber is of bilateral structure in that one wall 4, the bottom in the drawings, is of rigid construction; whilst the other, top wall 5 is of flexible construction. As shown the bottom wall is a sheet metal stamping 6. Between ends 7, 8 formed for inlet and outlet connection of the pump, the bottom stamping has a constant cross-section, shown in Figure 2. It is trough shaped with a central depression 9, shallowly sloping sides 10 and lateral flanges 11.

* The top wall is a moulded diaphragm 12 of reinforced elastomeric material. It has a central section 13 and edges 14, all having laterally and longitudinally extending reinforcement 15. This extends from the central section to margins 16 which are clamped to the flanges 11 of the bottom pressing by bolts 17 and a clamp pressing 18, which extends over the outside of the diaphragm as a cover. The reinforcement is conveniently provided in the form of a woven cloth. Engaging beneath the reinforcement cloth 15 are studs 19, which are incorporated into the diaphragm during its moulding. The studs are provided in pairs along the length of the diaphragm.

Above the diaphragm, a series of shoes 20 are provided along its length. Each shoe has a pair of slots 21 orientated in the longitudinal direction of the diaphragm. A respective one of the studs 19 engages in each slot, connecting the shoes to the diaphragm. The slots are dimensioned to allow the studs a certain amount of free play in their longitudinal direction. Above its slot each shoe has transverse pivot points 22 accommodating a pin 23, pivotally connecting the shoe to a respective boss 24 of an actuator A, details of some alternatives for which are given below, for movement of the diaphragm towards and away from the bottom stamping 6.

The downward movement of the actuators, shoes and diaphragm is largely as in a conventional peristaltic pump. However, insofar as the diaphragm has negligible upward resilience, return upward movement is driven by the actuators in accordance with my invention.

The efficacy of the pump is reduced if leakage occurs between the diaphragm, the shoes 20 are adapted to press the diaphragm into line contact 601 with the stamping with sufficient force to locally displace, longitudinally, some 602 of the elastomeric material of the diaphragm from between the shoe and the stamping, as shown in Figure 3. Typically the diaphragm is locally deformed beneath the shoe to the order of 85% to 90% of its free thickness. For this, each shoe is relieved at its up-and down-stream edges 25, 26, whilst providing line contact on its median line, which is its lowest point 27 in any cross-section taken longitudinal of the diaphragm. It should be noted that in the interest of showing the studs, Figure 3 is not a central cross-section of the shoes and does not show the lowest point 27 of the shoes. This is shown in figure 2. The bottom of the shoe is curved, whereby similar line contact is maintained if the shoe should become tilted slightly towards the inlet or the outlet as may occur on initial contact of the diaphragm with the stamping, when an adjacent section of the diaphragm is held up at a relatively steep angle. It should be noted that the diaphragm has only limited longitudinal extensibility, due to the reinforcement 15.

Tilting of the shoe with respect to its actuator A is accommodated by the pivot connection 22, 23.

When the diaphragm is lifted again, as shown at the left of Figure 3, the shoe lifts slightly away from the diaphragm, as permitted by the free play of the stud in the shoe, until stud comes under tension and lifts the diaphragm. This then creates suction on the inlet side of the portion of the diaphragm currently in contact with the bottom stamping. When, during the next cycle of the pump, the diaphragm is driven down again, the free play allows the stud to lift with respect to the shoe and not transmit localised high compression stress to the diaphragm. It should be noted that the top end of the stud does not abut the shoe as shown in Figures 3 & 4.

To enhance sealing of the diaphragm 12 to the stamping 6, the actuators A are preferably controlled to provide that an adjacent pair of them is always at bottom dead-centre in a sealing region of the diaphragm. This traps a small amount of fluid being pumped between the regions of line contact of the two adjacent shoes concerned, as shown in Figure 3. To allow for local upwards deflection of the diaphragm to accommodate this, and to allow for tilting of the shoes at mid-stroke, see Figure 3, the shoes are shorter than their-and the studs' 19-pitch 31. Conveniently the length 32 of the shoes is of the order of 75% to 80% of the pitch.

Transversely, the shoes are shaped to provide sealing contact of the diaphragm from one edge 33 to the other edge 34. Thus the bottom, transverse contour of the shoes at the line of their lowest points in longitudinal section has depressions 35 and shallowly sloping sides 36. The depressions are provided to accommodate increased thickness of the diaphragm at the studs 19, see Figure 4.

In operation, sequential ones of the actuators, that are in accordance with the numbering A1 A2, A3, A4, A5, A6, A7, etc. shown in Figure 5, drive their shoes downwards and then lift them up again. The control of the actuators is such that at any one time two shoes are fully depressed, compressing the diaphragm against the stamping, with one shoe to either side being in movement between the upper, withdrawn position and the lower depressed position. The timing is such that as one shoe first reaches its fully depressed position, the second one behind it is just about to lift off The intervening shoe is held fully depressed.

The shoes in mid-stroke are constrained by the non-extensible nature of the diaphragm to take up, at least partially, the slope of the diaphragm in passing from its withdrawn position to its depressed position. This results in the shoes pivoting about their connection 22,23 with the actuators A, which is accommodated by the pivotal connection. Further the axis of the actuators is slightly displaced due to the spacing of the pivotal connection above the studs 19. Freedom from these movements is provided by the curved bottom shape of the shoes and their length being shorter than the pitch of the studs along the diaphragm.

Because of constraint on the movement of the inlet and outlet ends 3 8,39 of the diaphragm, which are rigidly fixed, the first and last studs 19a,19o are held at fixed heights by their actuators A,A0 although the contoured ends of the diaphragm allows some longitudinal movement of these studs. The diaphragm is thicker and more rigid in these regions. The next-but-end studs 9a','9o' are driven by their actuators through only half the normal stroke, so as not to bring the diaphragm into contact with the stamping at their positions, in order not to over-work the diaphragm.

Turning now to Figure 6, there is shown a typical cam and return spring actuator. It comprises a cam lobe 40 on a camshaft 41 journalled above the diaphragm. The cam acts on a follower 42 having a stern 43 in a guide 44 in the cover 18. The foot of the stem is pivotally connected to the shoe 20. A spring 45 acting between the underside of the follower 42 and the cover 18 urges the follower up into contact with the cam * lobe and is of sufficient strength to lift the diaphragm to create suction in the inlet of the pump.

Turning onto Figure 7, the actuator there shown is similar to the previous one except that the spring return is replaced by a scotch yoke connection of a yoke 50 to an eccentric 51. This provides desmadromic drive for the diaphragm.

Figure 8 shows an arrangement similar to Figure 6, wherein the cam lobes are replaced by a spiral cam 60. Also in this Figure is shown a simpler bottom-stamping/diaphragmlcover configurant with a planar joint face 70. The simplicity in this respect is tempered by the inlet and outlet 71,72 being at right angles to the length of the pump chamber. There is also provision to support the diaphragm 12 against the outlet pressure, this shown by a shrouding shape 136 formed in the diaphragm cover 18, a separate pressure shroud can also be used.

Figure 9 shows another pump in which the actuators are electro-hydraulic 80, under the control of unit 81. This can move the shoes 20 and diaphragm 12 in precisely the same manner as described above, but with the additional feature of the end actuator being controlled to maintain a constant pressure in the pumps outlet. Peristaltic pumps are prone to send pressure waves along piping from the outlet. By suitable control of the end actuator 80, which can be arranged to act as a pressure sensor, the * sensed pressure can be controlled to be even. If necessary the next-but-one actuator also can be similarly controlled. Further, each actuator may be controlled to provide only a predetermined compression force by sensing of the force being exerted by the actuator, whereby the diaphragm will not be damaged if a foreign object is drawn into the pump and compressed beneath one of the shoes. Alternatively, where solid material, which is shatterable, is expected to be drawn in, should any shoe not reach bottom dead-centre due to the presence of solid material, the controller may be programmed to withdraw the shoe and advance it again with greater speed and force to crush the solid, possibly in successive operations.

Figures 10 and 11 show a differentially configured pump in which the pump chamber * 90 is toroidally configured with inlet and outlet 9 1,92 adjacent. Cam followers 93 are circularly arranged and acted upon by a pair of circularly moved cam elements 94 mounted radially from a drive shaft 95.

Figure 12 shows another pump, in which the individual actuators of the shoes are driven from a single source, namely a rodless, fluid-operated cylinder 101 having a pivotally-connected foot 102, which it strokes across the followers 103 of the actuators. For the return of the foot to the inlet 122 end of the pump, it is released by a fluid operated bolt 104 and allowed to lift under the action of a spring 105. At the inlet end of the stroke, the foot is forced down against the action of the spring by a ramp 106, so that the bolt can be re-engaged. The penultimate actuator has a -10 -transverse-acting, fluid operated lock 107 arranged to hold its follower down during the return stroke of the foot so as not to leave the pump chamber open to return flow.

The invention is not intended to be restricted to the details of the above described embodiments. For instance, for a wider pump chamber than that shown in Figure 2, the studs are widely spaced across the shoe with the result that the diaphragm is thinner between them. Thus the bottom stamping may have a central ridge to match this thinness. Again, the diaphragm and possibly the body may be constructed of more than one portion along its length, whereby portion(s) susceptible to high wear may be replaced without the need for replacement of the entire diaphragm. This construction is likely to embody, in effect, several pumps in series.

As regards the diaphragm itself, the reinforcement of this may be dispensed with where the diaphragm material is sufficiently tough, as shown in Figures 3,4 & 5. I anticipate that materials such as sold under the HYTREL mark by Dupont may be

suitable.

Figures 12 and 13 are cross-sections comparing the strain in diaphragm 12 with a peristaltic hose 125, for the extremes of flexing between fully open and shut. Figure 13 shows the diaphragm 12, lifted by stud 19 and shoe 20 into the open position; the * edge of 12 is clamped between cover 18 and body 123. Figure 13 also shows the diaphragm 12' now pushed by 20 onto 123. Figure 14 shows the peristaltic hose 125 sprung into the open position by its internal coil spring 137. Item 125' shows the peristaltic hose crushed against the peristaltic hose casing 124 by the rotating shoe 126. The strain in 12 is considerably less than that experienced by 125.

Figure 15 is a cross-section showing the use of an oscillating stem 127 and spherical bearing 138 to allow the shoe 20 to tilt longitudinally without transferring oscillations to shoe 20 and diaphragm 12.

Figure 16 is a schematic of another form of toroidal diaphragm pump. Items 2 and 3 are respectively inlet and outlet ports. The diaphragm 12 has studs 19, each fitted with a roller 131 engaged in a rotating shoe channel 130. The rotating shoe 128 rotates in direction 129 and in at least two places urges the diaphragm 12 against a seating in body 123. The diaphragm 12 is restored to its open position by track 130 lifting each stud 19 via rollers 131.

Figure 17 is a schematic view of another derivative of my invention. There are several separate diaphragms 12 mounted on a body 123 with several shoes 20. The body 123 may also comprise several conjoined parts. This variant caters for two requirements: (a) Large pumps where it is impractical to mould diaphragms of considerable length.

(b) Where one diaphragm 12 with shoes 20 is separately driven, operating as a macerator of the pumped fluid.

Figure 18 is again schematic showing diaphragm 12 and shoes 20, which are angled about the longitudinal axis. Such an arrangement of shoes is thought to give more consistent pumping when the media contains fibrous material. Shoes 20 can be irregularly spaced.

* Figure 19 shows in longitudinal section how the diaphragm 12 can be flexed using alternating vacuum and pressure in discreet chambers on the non-wetted side of the diaphragm. Items 2 and 3 are inlet and outlet; the fluid passes beneath several discreet vacuunilpressure chambers, 134 and 135. The diaphragm 12 is made with a plurality of transverse sealing beads. These sealing beads may be reinforced with clamping collars 133. The sealing beads abut ribs 139 which are within the diaphragm cover 18. 134 and 135 are sealed to atmosphere by clamping the diaphragm 12 between lateral flanges on cover 18 and body 123.

Figure 20 shows a cross-sectional view of an embodiment using a spring 45 urging a shoe 20 to press the diaphragm 12 onto a sealing position against the body 123. This is to be compared with the use of a spring shown in Figure 6. The shoe 20 is reciprocated by the rotation of a cam 40 driven by camshaft 41 rocking the cam-follower-arm about rocking-pin 141. 140 engages with stem-pin 142 which then reciprocates stem 43. One objective of this arrangement is to accommodate solid bodies 143 which may be trapped between diaphragm 12 and body 123. With the next lifting of diaphragm 12 the solid bodies are released and swept towards the outlet. This system is intended for pumping duties where solid objects 143 are common and the continuous operation of the pump via camshaft 41 is not interrupted.

It is envisaged that the majority of the pumping shoes 20 have this feature.

* Figure2l shows another method for accommodating solid objects 143 without interrupting the pumping sequence. The stem 43 is fitted with a stack of disc springs 144 which can be compressed when solid objects 143 are trapped between diaphragm 12 and body 123. The stem 43 is in two parts which are retained to each other by stem-pin 142. The free axial movement of both parts is resisted by springs 144. The design is not restricted to disc springs other fonns can be used to snub-out the reciprocation of the stem 43 arid ensure uninterrupted operation.

Figure 22 is a cross-sectional view showing the appearance of diaphragm 12, cover 18 and body 6 about the periphery of 12 after assembly. The outer face of diaphragm 12 is forced to adopt radius 145 on the cover 18.

Figure 23 shows the preferred as-moulded appearance of diaphragm 12. The moulded radius 146 is considerably greater than radius 145 on cover 18. When cover 18 and diaphragm 12 are assembled together a compressive stress is induced into the outer surface of diaphragm 12 and a tensile stress in the local underside of diaphragm 12.

The purpose of this is to reduce the stresses in diaphragm 12 when it is urged into contact with body 6 the tensile stress on the outer surface is reduced and the compressive stress within the underside is reduced. The flex life of diaphragm 12 is considerably greater than had the diaphragm 12 been moulded with radius 145 equal to radius 146. Radius 146 can be infinitely large when it becomes a straight line 148 tangential to diaphragm hump 149. This design technique of flattening diaphragm -13 -radius 146 can also be used when the diaphragm is moulded in the shut position relative to body 6. The radius on the underside of diaphragm 12 is made larger than body 6 radius 147. When the diaphragm 12 is drawn into the open position the stresses are reduced in the peripheral sections of the diaphragm 12.

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Claims (2)

1. CLAIMS1. A pump using a diaphragm, flexed in a wave-like manner upon a rigid body which induces a flow of fluid between inlet and outlet ports. The movement of the diaphragm is controlled externally by means of studs, or other elements, bonded into the diaphragm; these are actuated mechanically in an approximately sinusoidal sequence. When the diaphragm is pressed against the body a seal is made between vacuum and pressure areas of the fluid being pumped. The pumping sequence at all times maintains suction, prevents back-flow and pressurises the discharge. When compared with the hose type pump.The strains in the diaphragm in the sealed position are considerably reduced.The design of the diaphragm flattens the peripheral radius to further reduce the strain in the diaphragm as it is flexed. Also, allowing the shoes that compress the diaphragm against the body, to tilt as they are reciprocated, further reduces strains in the diaphragm. The diaphragm can be made in a wider range of elastomeric materials than the conventional hose, extending the fields of application. Because the diaphragm is positively opened and closed, as it were against the body, by external means rather than a coiled spring within a tube as used in a hose pump, operation can be much faster with considerable savings in energy use.
2. 2. The diaphragm can also be flexed by the application of a vacuum and pressure on the non-wetted face of the diaphragm, in discrete chambers.