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 pumping slurries and will

be described hereinafter with reference to this technological application. It will be

appreciated, however, that the invention is not limited to this particular field of use.

BACKGROUND OF THE INVENTION

In the past, various attempts have been made to transport slurries over relatively

long distances as a means, for example, of efficiently transporting coal, sand, cement

and minerals. In most cases, however, conventional pumping technology has been

found to be inadequate, because ofthe unusual fluid flow characteristics which many

slurries exhibit.

For example, positive displacement type pumps incorporating various

arrangements of pistons are often used to pump liquids. However, the vibrational

pulses imparted by pumps of this type can cause blockages in hydraulic transport

lines. Also, the valve characteristics inherent in piston type pumps typically render

them inadequate for handling larger particles.

Centrifugal pumps are also known and these tend to produce less vibration and

accommodate a larger range of particle size. However, because ofthe rotary nature of

such pumps, rapid wear is a common problem, particularly in shafts, bearings, seals

and the like which translate into high capital and maintenance costs.

Peristaltic pumps are also known. These typically comprise compression

elements such as pressure rollers which are passed in succession along the length of a flexible tube to induce fluid flow through the tube. In the past, however, such pumps

have typically been unable to generate sufficient pressure or flow rate to be effective

in large scale commercial operations. One problem is that if the tube is formed from a

material sufficiently strong to withstand high internal pressures, it is then resistant to

the required external compression from the pressure rollers, without relatively high

energy inputs and consequential inefficiency and rapid mechanical wear. On the other

hand, when more flexible tubes are used, these have a lower pressure capacity and a

tendency to collapse, particularly on the suction side, thereby substantially

diminishing the performance and efficiency ofthe pump. For these reasons, peristaltic

pumps have hitherto been generally confined to low pressure or flow rate applications,

such as in the medical field.

It is an object of the present invention to provide an improved pump which

overcomes or substantially ameliorates at least some of these disadvantages ofthe

prior art.

DISCLOSURE OF THE INVENTION

Accordingly, in a first aspect, the invention consists in a peristaltic type pump

including a flexible composite tube comprising a primary inner tube to contain a

primary fluid to be pumped and an outer jacket containing a secondary fluid,

compression means adapted periodically to produce peristaltic compression waves

along the composite tube thereby to induce flow ofthe primary fluid through the

primary tube, and conduit means to direct a counter flow ofthe secondary fluid from a

downstream section to an upstream section ofthe outer jacket, thereby tending to

expand the primary tube and enhance suction pressure upstream of the compression

waves. Preferably also, the secondary fluid is contained within a secondary flexible tube

spirally wound around the outside ofthe primary tube. In this embodiment, the

contained secondary fluid diverted from the downstream to the upstream sections of

the jacket through the conduit induces increased hoop stress in the spiral wound

secondary tube on the upstream side ofthe compression element, thereby expanding

the primary tube and creating additional suction pressure. Preferably, the conduit also

includes a stabilising fluid reservoir or manifold adapted to absorb transient

differential pressures and accommodate small volumetric changes. The secondary

fluid contained in the jacket and/or the stabilising reservoir may include a liquid or a

gas, or a combination of both, and may be pressurised if required.

Preferably, the compression means includes at least one compression element

adapted periodically to pass along the composite tube, from an inlet end toward an

outlet end, thereby producing said peristaltic compression waves.

Preferably, the pump includes a plurality of such compression elements, each in

the form of a pressure roller assembly adapted to run along the length of the primary

tube and the surrounding jacket. In the preferred embodiment, at least two sets of

complementary pressure roller assemblies are respectively disposed on opposing sides

of the composite tube such that the rube is progressively squeezed between opposing

rollers of each set. In this embodiment, each set of rollers preferably contains at least

three pressure roller assemblies supported on an endless chain or belt extending

around a pair of pulleys spaced apart along the length ofthe composite tube. The

length ofthe endless chain or belt, the spacing of the pulleys, and the number of roller

assemblies of each set are determined such that an opposing pair of rollers engages the

suction end ofthe tube before the preceding rollers disengage the downstream end of

the composite tube, thereby producing a continuous substantially pulse-free linear

pumping action.

Each opposing pair of roller assemblies is preferably urged into compressive

engagement with the composite tube by a pair of mutually opposed inwardly

depending guide tracks, the relative spacing of which may be selectively adjusted to

control the pressure and flow characteristics ofthe pump. Preferably also, a

replaceable wear resistant curtain is disposed between each set of pressure rollers and

the adjacent outer side wall ofthe composite tube. This minimises wear on the tube

by avoiding direct contact with the rollers.

The entire pump assembly is preferably housed within a sealed casing, which

can be selectively pressurised with a suitable liquid to reduce friction between the

various moving parts and enable the pump to accommodate higher intemal pressures.

According to a second aspect, the invention provides a flexible primary tube for

use with a peristaltic type pump as defined above, said tube being initially formed

with an elliptical profile in a relaxed condition, as manufactured.

Preferably, the elliptical profile ofthe primary tube is defined by a minor axis X

and a major axis Y, determined by the relationships:

X = P_ ; and Y = X x 7 ^{0 5} 2

where D is the nominal intemal diameter of the primary tube when fully expanded to a

circular cross-sectional profile.

In this way, the inner circumference ofthe primary tube does not substantially

change, despite variations in the cross-sectional profile during the compression cycles.

Advantageously also, the elliptical profile reduces the extent of maximum deformation

during each compression phase by effectively dividing the operational flexure into two

opposite phases of bending, about a median position corresponding to the relaxed

configuration ofthe tube, rather than a single bending phase of twice the magnitude.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments ofthe invention will now be described, by way of

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

Figure 1 is diagrammatic a cross-sectional side elevation showing a pump

according to a first embodiment ofthe present invention;

Figure 2 is a cross-sectional view showing the primary tube in more detail,

including longitudinal grooving on the inner surface ofthe tube;

Figure 3 is a diagrammatic cross-sectional side elevation similar to Figure 1 ,

showing a second embodiment ofthe invention;

Figure 3 A is an enlarged detail showing the compression profile ofthe pump of

Figure 3;

Figure 4 is a diagrammatic cross-sectional side elevation showing a third

embodiment ofthe invention;

Figure 5 is a side elevation showing a fourth embodiment ofthe invention;

Figure 6 is a longitudinal section showing the inner tube, the outer jacket, and

the intermediate spirally wound secondary tube;

Figure 7 is a transverse cross-section taken along line 7-7 of Figure 6 showing

the elliptical cross-section ofthe composite tube, in a relaxed configuration as

manufactured;

Figure 8 is a transverse section showing the composite tube of Figure 7 in a

compressed configuration; and

Figure 9 is a transverse section showing the composite tube of Figure 7 in an

expanded configuration.

PREFERRED EMBODIMENTS OF THE INVENTION

Referring firstly to Figure 1 , the invention provides a pump 1 comprising a

flexible primary inner tube 2 defining an inlet 3 and an outlet 4 at opposite ends. The

inlet and outlet incorporate flanges 5 enabling the pump to be serially connected in a

fluid pipe line. As best seen in Figure 2, the primary tube 2 consists of an inner layer

10 formed from relatively soft rubber or similar material with intemal grooves 1 1

running longitudinally along its length. These grooves enable the tube more readily to

accommodate the required deformation and subsequent restoration. An outer covering

12 of the inner primary tube encapsulates intermediate layers of fibrous reinforcement

13 to provide additional intemal pressure capacity.

As best seen in Figure 6, the pump further includes an outer jacket 15, again

suitably reinforced, which surrounds a secondary flexible tube 20 wound spirally

around the primary tube. Thus, the outer jacket 15 encases the primary and secondary

tubes together to form an integrated composite tube 21. In an altemative embodiment,

the secondary tube may simply be defined by a continuous spiral cavity formed within

a thick-walled flexible tube such that the primary tube, the secondary tube, and the

outer jacket are effectively integral. An integral tube in this form may be conveniently

manufactured from a single material in discrete longitudinal segments, and joined such

that the inner longitudinal conduit defining the primary tube and the spiral cavity

defining the secondary tube are effectively continuous. In a further variation, the outer

jacket may simply be defined by the secondary spiral tube itself, without the need for a

surrounding layer, or jacket as a separate and discrete element. This may require

attachment ofthe secondary tube directly to the primary tube (if not integral

therewith) in order to achieve the desired functionality whereby radial expansion of

the outer spiral tube effects a corresponding radial expansion ofthe inner primary tube

without separation between the two. In yet a further embodiment, the inner primary

tube and the outer jacket define one or more intermediate annular cavities to contain

the secondary fluid, without the need for a spiral tube or cavity per se.

A series of compression elements in the form of pressure roller assemblies 25

are adapted to run along the length ofthe composite tube. In the embodiments of

Figures 1 and 3, each roller assembly comprises a central primary roller and

surrounding secondary rollers of relatively smaller diameter so as to define a more

progressive compression profile. As best seen in Figures 3 to 5, two sets 26 of

multiple roller assemblies 25 are disposed on opposing sides ofthe composite tube. In

this case, each set 26 of rollers contains three roller assemblies 25 supported on an

endless chain 27 extending around a pair of pulleys 28 spaced apart along the length

ofthe tube. At least one of the pulleys of each pair is driven by a suitable drive

mechanism (not shown) to provide motive power for the pump.

Each opposing pair of roller assemblies 25 is urged into compressive

engagement with the tube by a corresponding pair of mutually opposed, inwardly

depending guide tracks 30 (see Figure 1), the relative spacing of which is selectively

adjustable via electro-mechanical linear actuators 32. With the guide tracks fully

retracted, the pressure rollers will be completely withdrawn from the tube and no

pumping will occur.

A replaceable wear resistant curtain (not shown) is disposed between each set of

pressure rollers and the adjacent side wall ofthe outer jacket 15 ofthe composite tube.

This minimises wear on the jacket by avoiding direct contact with the rollers.

In altemative embodiments, the compression means may take other forms

including electrically actuated piezoelectric compression elements, hydraulic

actuators, or pneumatic cylinders, which may operate either radially or axially to

induce the desired peristaltic compression.

A second embodiment ofthe invention is show in Figure 3, wherein

corresponding features are denoted by corresponding reference numerals. However,

the guide tracks 30 are omitted for clarity. In this instance, each roller assembly 25

incorporates seven individual rollers of different size, to define a smoother, more

progressive compression profile, as shown in more detail in Figure 3A.

A third embodiment ofthe invention is shown in Figure 4, wherein each roller

"assembly" 25 consists of a single, larger diameter roller. A further variation is shown

in Figure 5 where, again, corresponding features are denoted by corresponding

reference numerals.

As best seen in Figure 6, the jacket 15 surrounds at least a portion ofthe primary

tube, so as to locate the spirally wound secondary tube 20. Conduit means in the form

of a pressure equalising arrangement indicated generally at 40 allows a continuous

counter-flow of fluid contained in the secondary spiral tube between respective

downstream 41 and upstream 42 sections, whilst bypassing the intermediate pressure

rollers (see also Figure 5) as they move along the tube.

In the embodiment illustrated in Figure 6, the secondary spiral tube is divided

into segments A-B, B-C, C-D, etc., each comprising approximately seven rums having

a helix angle of between 1 ° and 20°, ideally around 5°. Transfer ports 43 extend from

a pressure equalising a manifold 45, allowing transfer ofthe secondary fluid between

adjacent segments ofthe secondary tube. The distance between the transfer ports 43 is

preferably less than or equal to the distance between adjacent pressure roller

assemblies 25. This arrangement enhances the pressure response ofthe system, and is

particularly suitable for embodiments where the composite tube is formed in discrete

longitudinal segments.

The fluid contained in the closed circuit defined by the secondary tube, the transfer ports, and the pressure manifold, which also acts as a stabilising reservoir,

may include a liquid or a gas, or a combination of both, and is pressurised as

appropriate to achieve the desired performance characteristics.

The entire pump assembly is housed within a sealed outer casing 50 (see Figures

1 and 5) which may be pressurised with a suitable fluid to reduce friction between the

various moving parts and to enable the pump to accommodate higher intemal

pressures. Conveniently, the surrounding fluid medium also enables the liquid being

pumped to be heated or cooled if desired.

Turning now to describe briefly the operation of the pump, the outer casing 50 is

first filled with liquid and pressurised to the desired pressure. The drive pulleys 28 are

then activated to progressively draw the roller assemblies 25 along the length of the

tube. As the pressure rollers successively run along the length ofthe tube toward the

outlet, they produce a corresponding compression wave inducing fluid flow through

- l i ¬

the tube. The lateral positions ofthe guide tracks 30 may be adjusted by actuators 32

to effect the desired pressured and flow rate characteristics (see Figure 1). The

spacing ofthe roller assemblies on the endless chain are such that there is always at

least one pair of opposing pressure rollers engaging the tube at any given time, and a

new pair of rollers engages the suction end ofthe tube before the preceding rollers

disengage the downstream end ofthe tube. This produces a continuous substantially

pulse-free linear pumping action. During movement ofthe pressure rollers along the

tube, the intermediate curtains prevent direct contact between the rollers and the tube,

to reduce wear. As the roller assemblies proceed along the length ofthe tube, the secondary fluid

contained within the spirally wound secondary tube 20 is progressively diverted from

the downstream to the upstream sections ofthe jacket, through the conduit

arrangement 40 comprising pressure manifold 45 and transfer ports 43 and hence

continuously bypassing each opposing pair of compression elements. This induces

increased hoop stress in the spiral windings of the secondary tube on the upstream side

ofthe pressure rollers, thereby tending actively to induce a circular cross-sectional

profile in the secondary spiral tube. This radial expansion ofthe secondary spiral tube

induces a corresponding radial expansion in the primary tube, and thereby creating

additional suction pressure. This performs a two fold function of maintaining the

optimum circular profile ofthe primary tube, which in prior art peristaltic pumps tends

to flatten over time, thereby optimising flow rate whilst also improving pumping

efficiency on the suction side of each compression wave.

Figures 7 to 9 show the shape and configuration of composite tube in more

detail. Referring firstly to Figure 7, the tube is initially formed with an elliptical

profile in the relaxed condition as manufactured, so as to reduce the extent of

maximum deformation during each compression phase. In terms of the pumping

cycle, the elliptical profile ofthe conduit in the relaxed condition as shown in Figure 7

corresponds to the configuration ofthe conduit mid- way through a compression phase.

In this way, it will be appreciated that the elliptical shape effectively divides the

operational flexure into two opposite (i.e. tensile and compression) phases of bending,

rather than a single phase of twice the magnitude. This in effect halves the maximum

extent of deformation from the relaxed or equilibrium condition.

Most preferably, the composite tube is formed on an elliptical mandrel having a

minor axis X and a major axis Y, as shown. If the internal diameter ofthe primary

conduit in the fully expanded circular condition is D, then the following relationships

are apphed :- X = D ; and Y = X x 7 ^{0 5}

2

The significance of these mathematical relationships is that the inner

circumference ofthe primary inner tube does not substantially change, despite

variations in the cross-sectional profile during the compression cycles, which

minimises internal stress and fatigue. However, the mean diameter of the spiral

defined by the secondary tube is necessarily larger than the inner diameter of the

primary tube and hence the mathematical identity no longer applies. Consequently,

pressurisation ofthe secondary tube still induces the desired change from elliptical to

circuiar profile on the suction side of each compression element, as described above.

This arrangement thus optimises the service life ofthe composite tube, and enables the

use of higher pressure capacity materials and designs which might otherwise lack the

required degree of flexibility.

Advantageously, the pump according to the present invention is applicable to a

wide variety of fluids and slurries with abrasive, corrosive or generally contaminate

characteristics. It also has the capacity to be set up to generate a reasonable flow with

only minimal compression by a dynamic pseudo wave action. It may therefore

accommodate relatively large particle size and may even be used to transfer live

specimens, such as fish, between storage tanks. The invention is also particularly well

adapted to pump relatively high viscosity liquids which in prior art pumps would

cause the peristaltic tube on the suction side to collapse under atmospheric pressure.

In all these respects, the invention represents 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.