GB2213044A

GB2213044A - Liquid-expressing apparatus and method of operation thereof

Info

Publication number: GB2213044A
Application number: GB8827576A
Authority: GB
Inventors: Stelio Storti
Original assignee: Pirelli Sistemi Antivibranti SpA
Current assignee: Pirelli Sistemi Antivibranti SpA
Priority date: 1987-12-01
Filing date: 1988-11-25
Publication date: 1989-08-09
Anticipated expiration: 2008-11-25
Also published as: FR2623746A1; GB2213044B; IT8722823A0; GB8827576D0; IT1223394B

Abstract

In liquid expressing apparatus for expressing juice from material e.g. fruits and vegetables contained between a rigid cylindrical bobbin having juice extraction passages 26 in its end flanges and a concentric tubular elastomeric membrane 7, by applying fluid pressure to the outside of the membrane to compress the material, in which the internal diameter of the cylindrical membrane 7 is too small to enable the axial introduction thereto of the bobbin and material, a reduced pressure is applied externally of the membrane to dilate it sufficiently to enable the bobbin loaded with material to be axially introduced to the membrane. The membrane has end flanges 8,9 with toothed portions 16,17 clamped between pairs of rings 10,11 and 12,13 forming end walls of cylindrical casing 18. The membrane has weaker portions 22,23,24,25 acting as hinges to enable the membrane to dilate from a position in which membrane 7 engages the material in the bobbin and its end flanges are perpendicular thereto to a position in which the centre of the membrane 7 engages the casing 18 and its end faces are bent about the edges of end walls 11,12. Vacuum is applied via the casing 18 to dilate the membrane and when fluid is introduced under pressure between casing and membrane 7, the membrane is reduced in diameter without wrinkling to compress the material in the bobbin. <IMAGE>

Description

LIQUID-EXPRESSING APPARATUS AND METHOD OF OPERATION THEREOF.

This invention relates to a liquid-expressing apparatus and to a method of operation thereof.

A liquid-expressing apparatus is known which is used to squeeze juices out of, for example, beetroots and fruits and which comprises an elastomeric membrane which is caused (by a suitably pressurised liquid) to press against the material from which juice is to be obtained, said material being carried by a bobbin-shaped carrier. The bobbin-shaped carrier has a right-cylinderical portion whose operative length is limited by annular flanges each of which is fixed to a respective one of the ends of said portion and each of which extends normal to the longitudinal axis of said portion. The annular compartment which is defined by the axially inwardly directed surfaces of the two flanges and the radially outwardly directed surface of the right-cylinderical portion is where the material to be pressed is accommodated.The elastomeric membrane has a tubular part at whose opposite ends there are annular flanges; at least a part of each flange is secured between a respective pair of plates which form part of a fixed supporting structure which itself forms part of said apparatus. The annular flanges of the membrane, as manufactured, extend normal to the longitudinal axis of the tubular part.

The known apparatus has a shaft which is connected to the supporting structure and which extends through the tubular part of the mounted elastomeric membrane along the longitudinal axis of said tubular part.

In use, the bobbin-shaped carrier, already loaded with the material from which juice is to be expressed, is slid along said shaft into the interior of the tubular part of said membrane; this is possible because the inside diameter of the tubular part is such as to provide an adequate clearance between the radially inner surface of said tubular part and the radially outer edge surfaces of the flanges of said bobbin-shaped carrier. A liquid under high pressure is now supplied to the space between the surfaces of the tubular part and the flanges of the membrane and a rigid wall which encircles said membrane and which forms part of said structure.Said applied pressure causes the deformable elastomeric membrane to compress the material with which the bobbin-shaped carrier is loaded, thereby expressing juice or other liquid; eventually, the annular body of compressed material will not be compressible any further and, at that stage, said material can be regarded as a substantially dry residue of solids from which all of the juice or liquid has been expressed.

It will be apparent from the description in the three preceding paragraphs that the rightcylindrical tubular part of the membrane is forced to assume a smaller diameter when it is applying compression to the material from which juice is to be expressed; this has the inevitable result that the elastomeric material becomes deeply and extensively folded and these folds become squashed by the high force of compression (generally of the order of from 60 to 70 atmospheres). During repeated use of the known apparatus, this squashing and flattening of the folds of elastomeric material leads to said material developing cracks and, eventually, tears or other ruptures. Obviously, tears and other ruptures would at the very least reduce the efficiency of the juice extraction process and would in time necessitate replacement of the damaged membrane.

The principal object of the present invention is to provide a new apparatus which is operable to obtain juice or other liquid by expression from many different types of crops (e.g. fruit or dry granular materials) and which is free from the major drawback discussed in the preceding paragraph. It is a subsidiary object of the present invention to provide a method of operation of said new apparatus.

According to a first aspect, the present invention consists in a method of expressing a liquid from a material, said method comprising the following steps, namely, (a) dilating from its at-rest or as-moulded condition an elastomeric membrane, which includes a rightcylindrical portion, by means of nagative pressure applied by vacuum pump to at last the radially outer surface of said portion; (b) placing inside said dilated membrane a carrier shaped like a bobbin and about which a quantity of said material has been packed so as to form an annulus whose outside diameter is of large size; and (c) thereafter using a pressurised liquid to cause the radially inner surface of said membrane to compress said annulus of material from all angles in order to change the outside diameter of said annulus from said large size to a small size which is that of the liquidexhausted residue of said material and which is equal to the inside diameter of the right-cylindrical portion of the membrane in its at-rest (as moulded)condition.

Preferably, during step (c), the pressure exerted by said liquid builds up gradually to a value of the order of 60 to 70 atmospheres.

According to a second aspect, the present invention consists in an apparatus for expressing a liquid from a material, said apparatus comprising a first part which includes an elastomeric membrane having, as moulded and in its at-rest condition, a right-cylindrical portion of a certain inside diameter; a second bobbin-shaped part which is adapted for being loaded with an annulus of said material, said annulus having an outside diameter which is greater than said certain diameter; first means operable to apply a negative pressure at least to said right-cylindrical portion of the membrane in order to effect dilatation of said membrane for the purpose of facilitating the insertion of the loaded bobbin-shaped part inside the membrane; and second means operable to cause the radially inner surface of said right-cylindrical portion to move radially inwardly for the purpose of compressing said annulus until its outside diameter is equal to said certain inside diameter.

In an apparatus as described in the preceding paragraph, said certain inside diameter may fall within the range from 500 mm to 2000 mm.

Said membrane may have a thickness, in its asmoulded or at-rest condition, a thickness which falls within the range from 5 mm to 20 mm.

In an apparatus as described in any of the three preceding paragraphs, the ratio between the diameter of the membrane in its at-rest condition and the diameter of said membrane in its condition of maximum dilatation, both measurements being made along a central plane which extends normal to the longitudinal axis of said right-cylindrical portion, preferably falls within the range from 0.4 to 1.

It is preferred that there are flanges at the opposite ends of said right-cylindrical portion, each flange being an annulus which extends away from and in a direction normal to the longitudinal axis of said portion, said flanges being clamped in a fluid-tight and liquid-tight manner between clamping devices.

In an apparatus as described in any of the five preceding paragraphs,there is further included a shaft whose longitudinal axis is coincident with that of said right-cylindrical portion of the membrane, said shaft being provided for said bobbin-shaped part to be moved along for insertion into or withdrawal from its position inside said membrane.

Each of the flanges hereinbefore mentioned may be formed with at least one hinge in a zone remote from that part of said flange which is clamped between said clamping devices.

In an apparatus as described in the preceding paragraph, there is preferably a hinge at the junction of each flange with the respective end of the rightcylindrical portion of the membrane.

In one embodiment of the apparatus as described in either of the two preceding paragraphs, in the condition of maximum dilatation of said membrane, the unclamped part of the membrane assumes a configuration which (1) includes an axially centralised portion which is in contact with a rigid wall of the apparatus and which is parallel to the longitudinal axis of said right-cylindrical portion, and (2) includes two additional portions each of which is attached to a respective end of said axially centralised portion and each of which not only extends towards said longitudinal axis but also makes an obtuse angle with said axially centralised portion.

In another embodiment of the apparatus as described in the second or third preceding paragraph, in the condition of maximum dilatation of said membrane, the unclamped part of the membrane assumes a configuration which (1) includes an axially centralised portion which is in contact with a rigid wall of the apparatus and which is parallel to the longitudinal axis of said right-cylindrical portion, and (2) the axually outer remaining portions of the membrane are folded concertina fashion.

Some embodiments of a liquid-expressing apparatus according to the present invention will now be more particularly described, by way of example only, with reference to the accompanying diagrammatic drawings, in which Figure 1 is a perspective view of part of a fixed supporting structure and other elements of said apparatus; Figure 2 consists of cross-sectional views, placed side by side for comparison, of an elastomeric membrane and a bobbin-shaped carrier; Figure 3 is an axial section through a portion of a first embodiment of said apparatus, showing the manner of behaviour of the elastomeric membrane; and Figure 4 is an axial section similar to that of Figure 3 but of an alternative embodiment of said apparatus.

Referring to Figures 1 and 2, there is illustrated, very diagrammatically and incompletely, a liquid-expressing apparatus 1 which essentially comprises a first part having a rigid right cylindrical container 2 inside which is disposed a membrane made of an elastomeric material, and a second part which is bobbin-shaped and has a right-cylindrical portion 3 at whose opposite ends there are flanges 4, 5 which are annular and which lie on parallel planes which are normal to the longitudinal axis of the portion 3. The bobbin-shaped part can be mounted for making sliding movements along a shaft 6; the manner of connection between said part and said shaft is not important and said connection could, for example, be effected by a series of spokes which extend radially outwardly from a sleeve to said part, said sleeve being slidable on said shaft.When mounted on said shaft 6, the longitudinal axis of said bobbin-shaped part is coincident with that of said shaft or substantially so.

The membrane hereinbefore referred to consists of a right-cylindrical portion 7 at whose opposite ends there are flanges 8, 9 which are annular and which lie on parallel planes which are normal to the longitudinal axis of said portion 7. Said flanges 8, 9 or at least parts of them are clamped between suitable elements (not shown) of a fixed supporting structure to which the shaft 6 is connected. The reference numeral 10 is intended to indicate the through-passageway which is delimited by the portion 7 and which can be increased in size (diameter) in the manner hereinafter described.

The membrane could be made, for example, of natural rubber or of a styrene butadiene rubber or of any other broadly equivalent material. Moreover, the generally preferred hardness of said elastomeric material from which the membrane is made is 65 Shore A, and the thickness of said elastomeric material of said right-cylindrical portion 7 falls within the range from 5 mm to 20 mm.

The material from which a liquid is to be expressed (e.g. fruit from which juice is to be taken) is packed around the portion 3 of the bobbin-shaped part up to the level which is represented by the diameter d in Figure 2. The diameter dl represents the level of the substantially dry or exhausted residue of said material after the liquid has been expressed therefrom and it will be noted that the internal diameter of the portion 7 of the cured or vulcanised membrane has a value D which is equal to that of the diameter dl. It must be stressed that the condition illustrated in the left-hand half of Figure 2 is the at-rest condition of the membrane and this at-rest condition is the condition of the membrane at the end of the liquid-expressing process.

Therefore, there cannot be any objectionable folding of the membrane under the high pressuresnecessary for liquid-expression and the disadvantage inherent in the operation of said known apparatus is avoided completely.

In preferred embodiments of the liquidexpressing apparatus according to the present invention, the membrane has a diameter D (described in the preceding paragraph) whose value falls within the range from 500 mm to 2000 mm, such membrane being for use with a bobbin-shaped part which is such that the material which is to be pressed can be built up to a level represented by the diameter d whose value falls within the range from 700 mm to 2400 mm.

The dimensional values, given above, for the membrane have been found to be particularly suitable for the achievement of correct dilatation of the portion 7 of said membrane by the use of reduced pressure acting on the radially outer surface of said portion 7 (as described later). This dilatation of the portion 7 facilitates the insertion of bobbin-shaped part and its flanges 4, 5 into the enlarged throughpassageway 10. In fact, the ratio between the diameter of the portion 7 in the at-rest condition of the membrane and the diameter of said portion 7 in its condition of maximum dilatation (both measurements being made on a central plane which is perpendicular to the longitudinal axis of the tubular membrane) falls within the range from 0.4 to 1.

Referring now to Figure 3, it will be seen that parts of the flanges 8, 9 attached to the opposite ends of the portion 7 of the membrane are clamped between pairs of rings 10, 11 and 12, 13, respectively.

The clamping effect is maintained by threaded bolts 14, 15 and the connection between said flanges 8, 9 and the surfaces between which they are sandwiched is improved by said surfaces being provided with serrations or toothings 16, 17.

The inner two rings 11, 12 have central apertures therein which are of larger diameter than those in the outer rings 10, 13; this is to facilitate dilatation of the membrane, as will become apparent.

As stated above, reduced pressure is applied to the radially outer surface of the portion 7 of the membrane by means of suction pumps. Said pumps are connected to the space which is bounded by a rightcylindrical wall 18 of the container 2, by the surfaces of the rings 11, 12, by the flanges 8, 9 of the membrane and by the portion 7 of said membrane.

Said space is also utilized for applying pressure, by way of said membrane, to the material from which liquid (e.g. juice) is to be expressed; in that case, a liquid under pressure is pumped into said space as will be described below. The vacuum pumps, the pumps for pumping liquid under pressure into said space and the other means enabling such reduced and elevated pressures to be applied to said space alternately are not shown but are considered to be within the competence of an engineer to provide.

The portion 7 of the membrane is connected to the flange 8 by means of spaced hinges which are created by the existence of cavities 22, 23 which are substantially of semi-circular cross-sectional shape; similar cavities 24, 25 create hinges by which said portion 7 is connected to the flange 9. In its at-rest condition, the portion 7 of the membrane extends parallel to the Dngitudinal axis of the first part of the apparatus and the major proportion of each flange extends radially outwardly away from said axis.

In its dilated condition, which is also illustrated in Figure 3, the membrane assumes the configuration in which a part 19 is in contact with the wall 18 (and is therefore parallel to said axis), two other parts 20, 21 extending away from the part 19 and towards said axis and also towards the respective rings 11, 12. It will be understood, of course, that the parts 20, 21 comprise some of the flanges 8, 9 and also the membrane portions which lie between the respective cavities 22 and 23 on the one hand and 24 and 25 on the other hand. It will also be seen from Figure 3 that the various parts 19, 20 and 21 are rectilinear and that said parts 20, 21 merge into those parts of the respective flanges 8, 9 which have been bent around the radially inner peripheries of the rings 11, 12.

The hinges created by the cavities 22, 23 and 24, 25 could be created by other constructions, it being realised that the hinges result from the reduction of the thickness of the membrane at those zones. It will be seen that the hinges are placed at the transition zones in which the right-cylindrical portion 7 (Figure 3) and the respective flanges 8,9 are interconnected.

In order to extract liquid from a material, the following sequence of operations is carried out: (a) said material (perhaps ground to smaller particule size) is packed around the bobbin-shaped part up to the diameter d (Figure 2), said material being kept in place by suitable circumferentially disposed sheets or covers which are deformable; (b) the suction pumps are started in order to achieve maximum delatation of the membrane; (c) the bobbin-shaped part with its loaded material is introduced into the container 2 along the shaft 6; (d) the suction pumps are stopped and the other pumps are started in order to force a liquid under pressure into the space bounded by the membrane and the rings 11, 12 and the wall 18 for the purpose of applying gradially increasing pressure to the membrane which is in contact with the sheets or covers enclosing said material; and (e) said pumps continue to pump the liquid in order to compress said material and in order to express the juice or other extractable liquid therefrom, until said material reaches the diameter d (Figure 2).

The juice or other liquid is forced out of the bobbin-shaped part through a suitable number of axially directed passageways 26 formed in the flanges 4, 5 thereof.

The final pressure of the liquid which is pumped into said space for the purpose of expression of said juice reaches a value of from about 60 atmospheres to about 70 atmospheres by the time the material has been compressed down to the diameter dl.

When the end of juice-expression has been reached, the liquid pump is shut off and the pressurizing liquid is drained off. Then, the space is once again connected to the suction pump and the membrane is sucked into its condition of maximum dilatation,whereupon the bobbin-shaped part is removed. This permits another cycle to be started.

Referring to Figure 4, the illustrated arrangement is quite similar to the one illustrated in Figure 3 except for the membrane and the manner in which the membrane behaves in order to achieve maximum dilatation. Thus, parts of the flanges are clamped between rigid parts which are bolted to one another and the remaining parts of said flanges are provided with cavities 30 which create hinges which connect rectilinear parts 28, 29 to one another. Said hinges permit the portion 7 of the membrane to move, under the influence of reduced pressure, in a radially outwards direction, towards the wall 18. This is achieved, as can be seen,by the unclamped portions of the flanges folding axially inwardly like a concertina or bellows.

It would, in addition, be possible to provide two cavities 31, 32 in each flange, said additional cavities having the same semi-circular cross-sectional shape as that of the cavities 30 and creating additional hinges to facilitate the concertina-folding of the membrane as it moves to maximum dilatation.

It will be seen that an operating difference between the Figures 3 and 4 embodiments is that, in the Figure 4 embodiment, quite a large portion of each flange lies against the surface 34 of the wall 18, as also does most of the portion 7 of the membrane. This last-mentioned feature (namely, of the portion 7 lying in contact with the wall 18 upon maximum dilatation being attained) is not illustrated in the interest of the drawing being easier to interpret.

Otherwise, the mode of operation of the Figure 4 embodiment is the same as that of the Figure 3 embodiment.

Some important features of the hinges provided by the cavities 30 (Figure 4) are (1) the ratio between the width 1 (measured between the hinges connecting the respective parts 28, 29) and the width L (which is the width.of the rightcylindrical portion of the membrane) falls within the range from 0.85 and 0.93, all measurements being made parallel to the longitudinal axis; and (2) the ratio between the distance H (measured from the longitudinal axis to said hinges) and the distance h (measured from the longitudinal axis to the radially outer surface of portion 7 of the membrane) falls within the range from 1.1 to 1.3.

The various hinges provided both in the Figure 3 embodiment and in the Figure 4 embodiment may be reinforced with a flexible tension-resistant fabric.

Discussing now the behaviour of the membrane during the various stages of the juice-expressing method, the following advantageous points should be noted: (a) When the loaded bobbin-shaped part has been inserted into the first part, the membrane starts (as soon as the vacuum pump has been stopped) to unfold gradually and radially inwardly under the influence of its elasticity until its entire surface is in contact with the material carried by said bobbin-shaped part.

(b) At the end of the pressing step, namely, when the material is in the form of a substantially dry residue because all or substantially all of the juice or other liquid has been expressed, the membrane will have returned to its at-rest condition.

(c) In the condition of maximum dilatation of the membrane, the flanges have undulations. These undulations gradually disappear as the pressure, applied by the pumped liquid during juice-expression, gradually builds up from nil to the highest value of about 60 atmospheres to 70 atmospheres. By the time that pressure has been reached, all of the undulations have disappeared because the membrane has been restored exactly to its as-moulded (or at-rest) condition.

(d) Folds in the membrane which will become squashed or flattened during juice-expression under pressure cannot occur in the methods described above with reference to the accompanying drawings.

The diameter D of the portion 7 of the membrane could, if desired, be slightly larger than the diameter dl (see Figure 2).

Moreover, one and the same membrane can be used to express juice or other liquid from materials whose dry-residue diameters dl differ from one another by as much as from 4 to 10%.

The flanges of the membrane, in the regions thereof which are clamped between the clamping rings of the apparatus, are provided with teeth on both surfaces; these teeth mesh with complementary teeth formed on the respective surfaces of said clamping rings. This arrangement ensures a very positive connection or anchorage for the membrane flanges.

Claims

CLAIMS:

1. A method of expressing a liquid from a material, said method comprising the following steps, namely, (a) dilating from its at-rest or as-moulded condition an elastomeric membrane,which includes a rightcylindrical portion, by means of negative pressure applied by vacuum pump to at least the radially outer surface of said portion; (b) placing inside said dilated membrane a carrier shaped like a bobbin and about which a quantity of said material has been packed so as to form an annulus whose outside diameter is of large size; and (c) thereafter using a pressurised liquid to cause the radially inner surface of said membrane to compress said annulus of material from all angles in order to change the outside diameter of said annulus from said large size to a small size which is that of the liquidexhausted residue of said material and which is equal to the inside diameter of the right-cylindrical portion of the membrane in its at-rest (as-moulded) condition.

2. A method as claimed in Claim 1, wherein, during step (c), the pressure exerted by said liquid builds up gradually to a value of the order of 60 to 70 atmospheres.

3. An apparatus for expressing a liquid from a material, said apparatus comprising a first part which includes an elastomeric membrane having, as moulded and in its at-rest condition, a right-cylindrical portion of a certain inside diameter; a second bobbinshaped part which is adapted for being loaded with an annulus of said material, said annulus having an outside diameter which is greater than said certain diameter; first means operable to apply a negative pressure at least to said right-cylindrical portion of the membrane in order to effect dilatation of said membrane for the purpose of facilitating the insertion of the loaded bobbin-shaped part inside the membrane; and second means operable to cause the radially inner surface of said right-cylindrical portion to move radially inwardly for the purpose of compressing said annulus until its outside diameter is equal to said certain inside diameter.

4. An apparatus as claimed in Claim 3, wherein said certain inside diameter falls within the range from 500 mm to 2000 mm.

5. An apparatus as claimed in Claim 3 or Claim 4, wherein said membrane has a thickness, in its asmoulded or at-rest condition, a thickness which falls within the range from 5 mm to 20 mm.

6. An apparatus as claimed in any of Claims 3 to 5, wherein the ratio between the diameter of the membrane in its at-rest condition and the diameter of said membrane in its condition of maximum dilatation, both measurements being made along a central plane which extends normal to the longitudinal axis of said right-cylindrical portion, falls within the range from 0.24 to 1.

7. An apparatus as claimed in any of Claims 3 to 6, wherein there are flanges at the opposite ends of said right-cylindrical portion, each flange being an annulus which extends away from and in a direction normal to the longitudinal axis of said portion, said flanges being clamped in a fluid-tight and liquid-tight manner between clamping devices.

8. An apparatus as claimed in any of Claims 3 to 7, which further includes a shaft whose longitudinal axis is coincident with that of said right-cylindrical portion of the membrane, said shaft being provided for said bobbin-shaped part to be moved along for insertion into or withdrawal from its position inside said membrane.

9. An apparatus as claimed in Claim 7, wherein each flange is formed with at least one hinge in a zone remote from that part of said flange which is clamped between said clamping devices.

10. An apparatus as claimed in Claim 9, wherein there is a hinge at the junction of each flange with the respective end of the right-cylindrical portion of the membrane.

11. An apparatus as claimed in Claim 9 or Claim 10, wherein, in its condition of maximum dilatation, the unclamped part of the membrane assumes a configuration which (1) includes an axially centralised portion which is in contact with a rigid wall of the apparatus and which is parallel to the longitudinal axis of said right-cylindrical portion, and (2) includes two additional portions each of which is attached to a respective end of said axially centralised portion and each of which not only extends towards said longitudinal axis but also makes an obtuse angle with said axially centralised portion.

12. An apparatus as claimed in Claim 9 or Claim 10, wherein, in its condition of maximum dilatation, the unclamped part of the membrane assumes a configuration which (1) includes an axially centralised portion which is in contact with a rigid wall of the apparatus and which is parallel to the longitudinal axis of said right-cylindrical portion, and (2) the axially outer remaining portions of the membrane are folded concertina fashion.

13. An apparatus as claimed in Claim 12, wherein the concertina-folding is facilitated by there being hinges at the opposite ends of said right-cylindrical portion and at the two zones just outside the clamped parts of the membrane and midway between said pairs of hinges, each hinge which is midway between two others being so positioned, in the at-rest condition of the membrane, that two portions of the flange interconnected by said hinge make a shallow V of which the included angle is obtuse and of which the junction of the limbs of the V is directed towards the mid-length point of the longitudinal axis.

14. An apparatus as claimed in Claim 13, wherein, in the at-rest condition of the membrane, the ratio between the dimension L of the membrane (Figure 4) and the dimension 1, measured parallel to the longitudinal axis, ranges from 0.85 to 0.93.

15. An apparatus as claimed in Claim 13, wherein in the at-rest condition of the membrane, the ratio between the dimension H (Figure 4) and the dimension 11, each dimension being measured radially outwardly from the longitudinal axis, ranges from 1.1 to 1.3.

16. An apparatus as claimed in Claim 9 or in any Claim which is appended to Claim 9, wherein each hinge is constituted by a portion of said elastomeric material of a reduced thickness and reinforced by a flexible tension-resistant fabric.

17. An apparatus as claimed in Claim 3 or in any Claim appended to Claim 3, wherein the right-cylindrical portion of the membrane has at each end an annular flange extending normal to and away from the longitudinal axis of said portion, a portion of each flange being clamped between a respective one of two pairs of clamping devices, each axially inner clamping device having a central aperture larger than that of its adjacent axially outer clamping device.

18. An apparatus as claimed in Claim 17 or Claim 7, wherein those portions of the flanges which are clamped between said respective clamping devices are formed with teeth on both surfaces, said teeth meshing with other teeth which are formed on the facing surfaces of the clamping devices.

19. An apparatus as claimed in any one of the preceding Claims 3 to 18, wherein the elastomeric material of the membrane is natural rubber.

20 An apparatus as claimed in any one of the preceding Claims 3 to 18,wherein the elastomeric material of the membrane is a styrolic rubber compound.

21. An apparatus as claimed in any one of the preceding Claims 3 to 20, wherein the elastomeric material of the membrane has a 65 Shore A hardness.

22. An apparatus constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying diagrammatic drawings.

23. A method of expressing a liquid from a material, substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.

24. Any features of novelty, taken singly o-r in combination, of the embodiments of the invention hereinbefore described with reference to the accompanying diagrammatic drawings.