WO2000001950A1 - Peristaltic pinch pump - Google Patents

Abstract

A peristaltic type pump (1) including an outer casing (2), a flexible conduit extending around an inner peripheral surface (11) of the casing (2), and a crank shaft (19) disposed axially within the casing (2), the crank shaft (19) having an eccentric lobe (21) disposed such that rotation of the crank shaft (19) periodically produces peristaltic compression waves along the conduit and thereby induces fluid flow through the pump (1).

Description

TITLE: PERISTALTIC PINCH PUMP

FIELD OF THE INVENTION

The present invention relates generally to pumps, and more particularly to

peristaltic type pumps.

The invention has been developed primarily for use in relation to the mining and

mineral processing industries for pumping slurries and the like, and will be described

primarily with reference to this application. It will be appreciated, however, that the

invention is not limited to this particular field of use.

BACKGROUND OF THE INVENTION

Peristaltic pumps are well known, and usually comprise a generally cylindrical

pump casing and a flexible conduit extending typically around a 180° sector of the

casing. A central rotor moves pressure cams or rollers, normally spaced apart by 180°,

around the conduit. The pressure cams or rollers are positioned to compress the conduit

as they pass along the operative sector within the casing. The conduit tends to spring

back into shape behind the cams or rollers by virtue of its inherent resiliency, although in

some instances a vacuum source may be used to assist the conduit in returning to shape.

The second cam or roller, normally mounted 180° from the first on the diametrically

opposite side of the rotor, comes into contact with the conduit at approximately the same

time as the first roller reaches the discharge point. In this way, the rollers alternately

produce peristaltic compression waves along the operative section of the conduit and

thereby induce fluid flow from the inlet to the outlet of the pump.

Such pumps are, however, known to suffer from a number of inherent

disadvantages. Firstly, a discharge pulse is induced in the fluid line each time one of the

pressure rollers passes the discharge point. This produces an uneven flow rate which is undesirable in many applications. In addition, pulsations or pressure waves caused by

the operation of such pumps have been known to cause damage to fluid pipelines. It is

known to attempt to reduce such pulsations or pressure waves by means of various

damping mechanisms. In practice, however, these have not been entirely effective.

A further disadvantage is that the conduit is subject to considerable tensile and

shear stress due to the action of the pressure cams or rollers running along its operative

length. This necessitates regular replacement of the conduits which is costly in terms of

capital equipment, downtime, and labour. In an attempt to extend service life, it is

known in some applications to seal the pump casing and to fill the chamber containing

the conduit with lubricant in order to reduce friction. However, whilst this is successful

to some extent in prolonging the service life of the conduit, it makes the task more

difficult, messy, time consuming and expensive when replacement is required.

Another disadvantage with conventional peristaltic pumps is that they are

essentially based around the use of a single hose or conduit. When more than one

conduit is used, the design of the pump necessitates positioning of the respective

discharge and suction ends of the conduits adjacent to one another, thereby exacerbating

the pulsation problem.

A further disadvantage with conventional peristaltic type pumps is that after a

number of compression cycles, the conduit begins to lose some of its initial elasticity and

tends not to return fully to its original circular cross sectional profile, in the relaxed state.

Rather, the hose tends to become permanently flattened, particularly on the suction side

of the pump where the problem is exacerbated by the relatively low internal pressure

within the conduit. This diminishes the overall performance and efficiency of the pump and again, necessitates frequent replacement of the pump conduit, at considerable

inconvenience and cost.

It is an object of the present invention to provide a pump which overcomes or

substantially ameliorates at least some of the disadvantages of the prior art.

DISCLOSURE OF THE INVENTION

Accordingly, the invention as presently contemplated provides a peristaltic type

pump including an outer casing, a flexible conduit extending around an inner peripheral

surface of the casing, and a crank shaft disposed axially within the casing, the crank shaft

having an eccentric lobe disposed such that rotation of the crank shaft periodically

produces peristaltic compression waves along the conduit and thereby induces fluid flow

through the pump.

Preferably, the pump further includes a plurality of pinch bars disposed in a radial

array within the casing, each pinch bar being slidable radially between an outer position

wherein an adjacent portion of the conduit is compressed between the pinch bar and the

inner surface of the casing and an inner position permitting expansion of the conduit,

such that rotation of the crank shaft progressively and sequentially displaces the

respective pinch bars from the inner to the outer positions.

In the preferred embodiment, an annular compression roller is disposed radially

between the eccentric lobe on the crank shaft and the radial array of pinch bars, such that

upon rotation of the crank shaft, the crank lobe causes the compression roller

progressively to revolve eccentrically around the inner edges of the pinch bars, thereby

to produce peristaltic compression in the conduit. In an alternative embodiment, the crank lobe may be configured to act directly on the pinch bars, in which case an

intermediate compression roller is not required.

Preferably, the pump conduit enters and exits the casing via respective slots or

ports, and defines an operative sector extending through at least 180°, and more

preferably through at least 360°, within the casing.

In the preferred embodiment, each pinch bar is constrained for substantially radial

sliding movement within a corresponding pair of parallel, spaced apart, radially

extending guide slots formed in opposite axial faces of the casing. The axial faces are

preferably defined by removable end plates.

In one preferred embodiment, the pump includes a plurality of discrete hoses or

conduits, positioned such that the respective inlet and discharge points are

circumferentially spaced apart, thereby tending to even out the pressure pulses and

produce substantially constant flow. In a preferred embodiment of this form of the

invention, the respective inlet and discharge points are spaced uniformly around the 360°

extent of the cylindrical casing to minimise pulsation. Preferably also, the pinch bars are

spaced uniformly around the casing. Preferably, the pump includes a single inlet and

outlet flange connected to manifolds for splitting the inlet flow into the discrete hoses or

conduits and combining the discharge from each hose.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way of

example only, with reference to the accompanying drawings in which: -

Figure 1 is a front elevation view showing a pump according to the present

invention; Figure 2 is a plan view showing the pump of Figure 1;

Figure 3 is a side elevation showing the pump of Figures 1 and 2; and

Figure 4 is a simplified schematic view showing the configuration of the eccentric

cam lobe, compression roller, pinch bars and pump conduit of the pump shown in

Figures 1 to 3.

PREFERRED EMBODIMENT OF THE INVENTION

Referring to the drawings, the invention provides a peristaltic type pinch pump 1

comprising an outer casing 2. The casing is defined by a generally cylindrical tubular

body 3 and axially spaced apart end plates 4. The tubular body 3 and end plates 4

together define an internal pump chamber 5, which is generally circular in cross

sectional profile.

The pump further includes a flexible conduit, hose or conduit 10 which extends

circumferentially around an inner peripheral surface 11 of the tubular body 3 as best seen

in Figure 4. A plurality of pinch bars 12 are disposed in a radial array within the

chamber 5 of the casing. Each pinch bar 12 is constrained for substantially radial sliding

movement within a corresponding aligned pair of parallel, spaced apart, radially

extending guide slots 13 formed in the respective end plates 4 of the pump casing. In

this way, each pinch bar is slidable radially between an outer position wherein an

adjacent portion of the conduit 10 is compressed between the pinch bar 12 and the inner

surface 11, and an inner position permitting expansion of the adjacent portion of the

pump conduit. In Figure 4, the pinch bars toward the bottom of the casing are shown in

the outer positions with the conduit compressed whereas the pinch bars disposed toward

the top of the casing are shown in the inner positions with the conduit relaxed. The pump further includes a crank shaft 19 disposed axially within the casing and

rotatably driven by a motor 20 or other suitable drive means. The crank shaft includes

an eccentric lobe 21. An annular compression roller 22 is disposed radially between the

eccentric lobe 21 on the crank shaft and the radial array of pinch bars 12. Upon rotation

of the crank shaft, the crank lobe causes the pressure roller to revolve and roll

eccentrically around the inner edges of the pinch bars. In this way, rotation of the crank

shaft progressively and sequentially displaces the respective pinch bars from the inner to

the outer positions, and back again. This periodically produces peristaltic compression

waves along the operative length of the conduit and thereby induces fluid flow through

the pump.

As best seen in Figure 4, the conduit enters and exits the tubular body 3 of the

casing via respective circumferential inlet and outlet ports 25 and 26. These ports are

configured such that the operative sector of the conduit extends through an angle of at

least 180°, and ideally at least 360°, within the casing. In the preferred embodiment, the

conduit extends around the inner periphery of the body of the casing for marginally

greater than 360° to provide an extent of overlap, which prevents back-flow through the

pump.

In an alternative embodiment of the invention, (not shown), the pump includes a

pair of conduits, positioned such that the respective inlet and discharge ports 25' and 26'

are circumferentially spaced apart from one another around the periphery of the casing.

The discharge lines are joined together immediately downstream of the pump via a Y-

connection and similarly, the suction lines are joined together by a Y-connection,

immediately upstream of the pump. It will be appreciated that by circumferentially staggering the respective inlet and discharge points, the pressure pulses are reduced in

magnitude for a given set of output pressure and flow rate characteristics. The pulses are

also spaced closer together, tending generally to produce a more constant flow. It will be

appreciated that additional conduits may be provided with larger casings, in which case

the respective suction and discharge lines may be joined by manifolds. A greater

number of circumferentially staggered conduits tends progressively to produce smaller

pressure pulses and more uniform flow. This reduces or substantially eliminates the

pulsation problems inherent in known peristaltic type pumps.

In a further refinement of the invention (also not shown), a short length of conduit

can be positioned to extend from the internal pump chamber 5, part way around the inner

surface of the casing, and out through a discharge port to atmosphere such that operation

of the pump tends to evacuate the pump chamber 5, which is otherwise sealed. The

resultant negative relative pressure within the chamber tends to expand the main pump

conduit(s) on the suction side, thereby tending to avoid or at least minimise the problem

of the conduits becoming permanently flattened on the suction side after prolonged use.

Preferably, the conduit is of a one way design or, alternatively, utilises a non-return

valve to prevent air flowing back into the pump casing. This could also be achieved by

utilising a mechanical arrangement in which, for example, a piston is acted on by one or

more pinch bars. This preferred modification to the invention ameliorates a fundamental

problem inherent in known peristaltic pump designs.

It will also be appreciated that because the pinch bars 12 are constrained by the

respective guide slots 13 to move solely in a radial direction, the compressive forces

applied to the pump conduit are exclusively radial. Because there are no pressure cams or rollers being dragged longitudinally over the conduit, tensile and shear stresses are

almost entirely eliminated which substantially prolongs conduit life. Again, this

addresses a fundamental failing of known peristaltic pumps.

A further advantage of the present invention is that when the pump conduits are

eventually worn and require replacement, this is a straightforward procedure which

simply involves removing one of the end plates and axially sliding out the pinch bars.

This in turn allows the removal of the conduit, with installation simply being a reverse of

this procedure. Again, this represents a significant improvement, particularly over prior

art pumps where the casing is sealed and filled with a lubricating fluid. It should be

reiterated that the present invention does not require such lubrication, since the

peristaltic compression is achieved solely by radial compressive forces. In all these and

other respects, the invention presents a commercially significant improvement over the

prior art.

Although the invention has been described with reference to specific examples, it

will be appreciated by those skilled in the art that the invention may be embodied in

many other forms.

Claims

1. A peristaltic type pump including an outer casing, a flexible conduit extending

around an inner peripheral surface of the casing, and a crank shaft disposed axially

within the casing, the crank shaft having an eccentric lobe disposed such that rotation of

the crank shaft periodically produces peristaltic compression waves along the conduit

and thereby induces fluid flow through the pump.

2. A peristaltic type pump as claimed in claim 1 wherein the pump further includes a

plurality of pinch bars disposed in a radial array within the casing, each pinch bar being

slidable radially between an outer position wherein an adjacent portion of the conduit is

compressed between the pinch bar and the inner surface of the casing and an inner

position permitting expansion of the conduit, such that rotation of the crank shaft

progressively and sequentially displaces the respective pinch bars from the inner to the

outer positions.

3. A peristaltic type pump as claimed in claim 2 wherein an annular compression

roller is disposed radially between the eccentric lobe on the crank shaft and the radial

array of pinch bars, such that upon rotation of the crank shaft, the crank lobe causes the

compression roller progressively to revolve eccentrically around the inner edges of the

pinch bars, to thereby produce peristaltic compression in the conduit.

4. A peristaltic type pump as claimed in any one of claims 1 to 3 wherein the conduit

enters and exits the casing via respective ports, the ports being configured such that the

conduit has an operative sector extending through an angle of at least 180° within the

casing.

5. A peristaltic type pump as claimed in claim 4 wherein the ports are configured

such that the conduit has an operative sector extending through at least 360° within the

casing.

6. A peristaltic type pump as claimed in any one of claims 2 to 5 wherein each pinch

bar is constrained for substantially radial sliding movement within a corresponding pair

of parallel, spaced apart, radially extending guide slots formed in opposite axial faces of

the casing.

7. A peristaltic type pump as claimed in claim 6 wherein the axial faces are defined

by removable end plates.

8. A peristaltic type pump as claimed in any one of claims 1 to 3 wherein the pump

includes a plurality of discrete hoses or conduits, positioned such that respective inlet

and discharge points are circumferentially spaced apart, thereby tending to even out the

pressure pulses and produce substantially constant flow.

9. A peristaltic type pump as claimed in claim 8 wherein the respective inlet and

discharge points are spaced uniformly around the 360° extent of the cylindrical casing to

minimise pulsation.

10. A peristaltic type pump as claimed in any one of claims 2 to 9 wherein the pinch

bars are spaced uniformly around the casing.

11. A peristaltic type pump as claimed in any one of claims 1 to 10 wherein the pump

includes a single inlet and outlet flange connected to manifolds for splitting the inlet

flow into the discrete hoses or conduits and combining the discharge from each hose.