EP1023538A1

EP1023538A1 - Spiral vacuum pump

Info

Publication number: EP1023538A1
Application number: EP97938731A
Authority: EP
Inventors: René GIGON
Original assignee: Ateliers Busch SA
Current assignee: Ateliers Busch SA
Priority date: 1997-09-16
Filing date: 1997-09-16
Publication date: 2000-08-02
Also published as: AU731955B2; AU4109597A; CA2304018A1; WO1999014502A1; US6290477B1; JP2001516848A; KR20010023800A

Abstract

The invention concerns a pump with spirals comprising means (29, 19, 19A) for preserving a minimum clearance between the joints (5) arranged on the ridges of each spiralling wall (27, 28, 33, 34) and the flat wall (25, 26, 31, 32) facing it. Such an arrangement, which is made possible by the low pressure difference prevailing between the two adjacent transfer chambers (50, 51), prevents the wear of the joints, the soiling of the transfer chambers as well as overheating caused by friction between the joints.

Description

Spiral vacuum pump

The present invention relates to a spiral vacuum pump, in particular the means for ensuring a certain seal between the movable part and the fixed part of the pump.

Spiral vacuum pumps are generally known in the art. They consist in particular of a fixed envelope portion supporting at least a first wall in the form of a spiral, and a movable portion, supporting at least a second wall in the form of a spiral, moving in an orbital motion at the inside said envelope portion. The two spirals being nested one inside the other, the orbital movement of the spiral mounted on the movable portion relative to the spiral mounted on the fixed envelope portion creates a change of shape and a displacement, along said spirals, a plurality of transfer chambers, each limited by a wall portion of the fixed casing portion, the movable portion and two spirals. Considering a transfer chamber, its movement thus brings a quantity of gas or air introduced into said chamber when the latter is at one end of said spirals towards the other end of said spirals where said quantity of gas or air can escape. In the case where gas or air is introduced from the outside of the spirals to be extracted towards the inside of the spirals, there is a decrease in the volume of the transfer chamber between these two points, respectively an increase in the pressure gas or air.

The advantage of such pumps is that they can work completely dry, that is to say that no lubricant comes into contact with the gas or the pumped air which cannot therefore be contaminated, so that they are particularly suitable for laboratories, the chemical industry, the food industry, etc.

An important problem of known pumps consists in ensuring the tightness of the transfer chamber, between the edge of the fixed spiral and the wall portion of the movable portion which faces it as well as between the edge of the movable spiral and the wall portion of the fixed envelope portion which faces it, respectively between the transfer chambers.

One known way of solving this problem consists in allowing a slight axial movement of the movable portion on its axis, and in ensuring the sealing of the transfer chamber by placing a seal disposed in a groove running along the edges of the spirals, said seals coming into sliding contact against the walls which face them, thus causing the movable portion according to an orbital movement to center itself inside the fixed envelope portion. Given the sliding contact mentioned, the seal must be a wear seal, that is to say relatively rigid, respectively having only little elasticity. In order to allow the dimensional adaptation of the seals to ensure the sealing of the transfer chamber, a first method consists in interposing a flexible seal between the bottom of the groove and the wear seal; the dimensional adaptation being produced by the flexible joint. A major drawback of this solution comes from its high cost. A second method consists in providing an air circulation channel between the bottom of the groove and the sliding joint, this air circulation channel having an intake orifice at a place in the spiral where the air is relatively high pressure. One of the drawbacks of this method comes from the irregularities of effect between various operating modes of the pump. On the other hand and generally, these systems where the seals are in sliding contact with a wall lead to wear of said seals, or to fouling of the transfer chamber and the need for frequent change of seals, as well as 'to a heating of the walls on which the joints slide. In addition, sealing is not guaranteed in the same way between new seals and worn seals, leading to a deterioration in the performance of the pump during use.

A first object of the invention is therefore to propose a spiral vacuum pump which does not meet the mentioned drawbacks of known pumps.

For this, the proposed pump avoids using seals in sliding contact on a wall; on the contrary, a very slight clearance is left during the mounting of the pump between the seal and the wall which faces it. This first provision avoids having to install an elastic means under the joint. In addition, in order to avoid that, contrary to what is desired, the seal inadvertently comes into sliding contact with the wall, the movable portion is mounted on its axis so as to have no possible axial movement. Thus, all the problems of friction, wear and overheating between the fixed and movable portions are avoided, while ensuring sufficient sealing of the transfer chamber. A second embodiment makes it possible to completely remove the joints between the fixed and mobile portions.

Another problem with spiral vacuum pumps is the unbalance created by the movable portion mounted eccentrically relative to the drive axis, thus causing vibrations when the vacuum pump is in operation. In known manner, one or more counterweights adjoining the drive shaft make it possible to achieve static balancing of the rotating masses. In the case of a vacuum pump, the movable portion of which comprises two spiral walls each disposed on one face of a central wall, a 180 ° offset between the two spirals already makes it possible to substantially reduce the imbalance of the rotating masses. This arrangement also has the advantage of reducing the gas or air vacuum peaks at the inlet of the pump by a factor of two, respectively the pressure peaks at the outlet of the pump, while doubling their frequency. . However, in operation, vibrations from a lack of dynamic balancing can act on the movable part and not allow the clearance described above to be maintained between the seal and the wall facing it. To avoid this, the mobile portion of the vacuum pump is also dynamically balanced.

In order to achieve the set goals, there is provided a scroll vacuum pump having the features of the main claim, particular variants or embodiments being described in the dependent claims.

The following description of a preferred embodiment of a spiral vacuum pump according to the invention is to be considered with reference to the appended drawing comprising the figures where: FIG. 1 represents a view in longitudinal section of a preferred embodiment of a spiral vacuum pump according to the invention,

FIG. 2 represents a cross-sectional view along the line II-II of the previous figure,

FIG. 3A represents an enlarged sectional section of a spiral joint,

FIG. 3B represents the same portion of the device in the embodiment without joint, and

FIG. 4 represents an enlarged sectional view along line IV-IV of FIG. 2.

Figure 1 shows a preferred embodiment of a scroll vacuum pump 1 seen in section along its longitudinal axis. The pump shown is composed of a drive part 10, in this case an electric motor, of a coupling part 11 as well as of the pump body 12, these three elements being connected by an external carcass 13, it - even mounted on a chassis 14. The pump body 12 essentially comprises a fixed portion 2 and a movable portion 3.

In this embodiment, the fixed portion 2 is composed of two half-shells 20 and 21, fixed together by fixing means such as for example the screws 22, the half-shell 20 being fixed to the carcass 13, respectively to the frame 14, by other fixing means such as for example the screws 23. A circular seal 24 seals between the two half-shells 20 and 21. The bottom walls 25, respectively 26, of the two half-shells 20 and 21 are essentially plane along a plane perpendicular to the axis 15 of the pump and each comprise a spiral wall 27, respectively 28, projecting perpendicularly to said bottom walls 25 and 26, and extending from a region close to the large diameter part of the wall 25 or 26 towards a region close to the center of each of the same walls. The movable portion 3 is composed of a central disc 30 supporting on each of its opposite faces 31 and 32 a spiral wall 33, respectively 34, projecting perpendicularly to said faces 31 and 32, and extending from a region close to the part of large diameter of the face 31 or 32 towards a region close to the center of each of the same faces.

Figure 2 which is a section along the line ll-ll of Figure 1, shows the half-shell 20 and the spiral 28 which is adjacent to the half-shell 21, as well as the central disc 30 and the spiral 34 which is attached. We see that the two spirals 28 and 34 have the same development and are nested.

The disc 30 is mounted in its center on a shaft portion 16 mounted eccentrically to the axis 15 of the drive shaft 17 of the pump (see Figure 1); on the other hand, the disc 30 is guided by eccentric guide means 4 (see Figure 2). Thus, the disk 30, respectively the whole of the mobile portion 3 has an orbital movement during the rotation of the drive axis 17. As can be seen in FIG. 2, this orbital movement between the mobile spiral 34 and the fixed spiral 28 creates a change in shape, a displacement as well as a reduction in volume of a transfer chamber 50 disposed between the walls of the two said spirals, leading to an admission and compression of the gas or air that 'it contains. As indicated above, the same arrangement of spirals 27 and 33 is provided on the other side of the disc 30, for the same effect.

It will be understood from the foregoing that an important point of the device consists in sealing the transfer chamber during the orbital movement of the mobile portion 3. Referring to FIG. 3A, an enlarged portion of an edge is seen. of the mobile spiral 34 opposite the bottom wall 26 of the half-shell 21. The problem and the figure would be identical in the case of the other mobile spiral 33 or fixed spirals 27 or 28 facing the walls which make them respectively face.

During its orbital movement, the upper edge 34A of the spiral 34 scans a portion of the surface 26. According to this embodiment, the spiral 34 has a seal 5 on its upper edge 34A in order to separate two transfer chambers 50 and 51 arranged on each side of the spiral 34. The seal 5 has the same spiral shape as the spiral wall which supports it, being fixed in a grooved housing 34B arranged in the edge 34A. Since this seal must be able to slide on the wall 26, it is generally fairly rigid and is not very compressible. In the pumps existing to date, in order to seal between the transfer chambers 50 and 51, pressure means were provided under the seal 5 in order to press the upper face 52 of said seal against the wall 26. These pressure means consisted either of a second elastic seal disposed at the bottom of the housing 34B, or of a gas or air pressure chamber provided in the bottom of the housing 34B. As indicated previously, these means led to heating due to the friction of the seal against the wall, to wear of the seal and fouling of the transfer chambers.

The solution proposed here takes into account the fact that two opposite transfer chambers on a spiral, the two chambers 50 and 51 in the example shown, are at pressures that are relatively little different from each other on a given portion of surface 26, respectively for a determined angular position of the orbital movement (see figure 2). In fact, if the absolute pressure in a transfer chamber increases regularly during its passage from the start of the spiral towards the center thereof, the pressure difference between two contiguous chambers is relatively small. Thus an absolute seal is not necessary. The device therefore comprises, according to this embodiment, a joint 5, rigid or semi-rigid, non-deformable, mounted in a grooved housing 34B with an edge 34A of the spiral 34. The entire device is mounted so as to leave a minimum clearance, of the order of 0 to 5 hundredths of a mm between the upper face 52 of the seal 5 and the wall 26. This minimal clearance makes it possible to avoid the drawbacks mentioned above, namely heating of the seal against the wall , the wear of the seal and the fouling of the transfer chambers. The seal 5 has been shown here as having a flat upper surface 52; such an arrangement is not absolutely necessary, this surface could also be curved or have an edge line facing the wall which faces it, the important thing being the minimal clearance mentioned which must exist between the portion of the joint closest to the wall facing it and said wall. According to a second embodiment shown in FIG. 3B, the seal 5 has been removed and it is directly the upper edge 34A of the spiral 34 which is separated from the wall which faces it by a clearance between 0 and 5 hundredths of a mm. As before, it is not essential that this upper edge is planar.

In order to guarantee this clearance between the seal 5, respectively the edge 34A and the wall which faces it, special precautions must be taken for the mounting of the movable portion 3 relative to the fixed portion 2. First, in order to to guarantee a determined spacing between the walls 25 and 26 of the two half-shells 20 and 21, a circular shim 29 of determined thickness can be placed between the two half-shells 20 and 21 (see FIG. 1). Similarly, the axial movement of the movable portion 3, respectively of the disc 30 carrying the spirals 33 and 34 can be eliminated by rolling bearings without play 19, the setting of the disc 30 on the eccentric bearing 16 also being obtained by shims, arranged in suitable places such as, for example, shims 19A. Thus, the disc 30 carrying the spirals 33 and 34 can be exactly centered in the space situated between the walls 25 and 26 of the half-shells 20 and 21, leaving a determined clearance, of the order of a few hundredths of mm between the joints 5, respectively the upper edges of the spiral walls, and the walls 25 or 26 which face them.

The need to maintain a constant clearance between the joints or the edges of the spiral walls and the walls which face them implies suppressing the vibrations caused by the orbital movement of the movable portion 3 as well as by the rotation of all the rotating parts. of the device, that is to say in particular the motor rotor as well as the ventilation means. For this, balancing means 6 are provided. A first balancing means consists in providing one or more counterweights 60 mounted in rotation with the axis of rotation 15 of the movable portion 3. For this, a first fixing disc 61 is fixed on the end of the portion of shaft 18A close to the drive shaft 17, and a second fixing disc 62 is fixed to a portion of shaft 18, aligned on the axis 15 and disposed on the other side of the eccentric portion 16, the counterweights 60 being fixed on said fixing discs 61 and 62. It can be seen in FIG. 1 that, to save space, the two discs attachment 61 and 62 are juxtaposed with wheels carrying the ventilation means 63 of the pump and the motor, without this being absolutely necessary for the operation of the pump according to the invention. The mass and the position of each of the counterweights 60 are determined in a known manner for static balancing in order to counterbalance the unbalance created by the eccentric movable portion 3 as well as other unbalances of the rotating parts. In order to reduce this imbalance, a second balancing means consists in angularly shifting the spirals 27 and 33 by 180 ° relative to the spirals 28 and 34. Referring to FIG. 2, if we see that the intake openings of the spirals 28 and 34 are located approximately at 7 a.m. according to an hourly dial, the spirals 27 and 33 arranged on the other side of the disc 30 and not visible in the figure have their intake openings located approximately at 1 o'clock on the same hourly dial. Such an arrangement slightly reduces the unbalance of the mobile portion 3. Another advantage of such an arrangement being that by putting in parallel the gas and air inlets and outlets of the spirals on the intake orifices, respectively discharge of the pump, the amplitude of the gas or air pressure pulsations is halved while the frequency of said pulsations is doubled. There is therefore a suction, respectively a more regular expulsion of gas or air.

The two balancing means mentioned provide static balancing of the movable portion 3 of the pump; in order to guarantee that the play of a few hundredths of a mm on the seals mentioned above are maintained during the operation of the pump, a dynamic balancing of the entire rotating part of the device is also carried out according to a known dynamic balancing technique . FIG. 1 shows small masses 64 and 65 respectively disposed on the ventilation means 63, which were fixed during this dynamic balancing operation.

It has been mentioned previously that the central disc 30 is guided by eccentric guide means 4. Referring to FIG. 2, it can be seen that the device here comprises three guide means 4. These guide means are intended to prevent that the central disc 30 rotates with the rotation of the eccentric scope 16, but has the desired orbital movement. For this, and as can be seen in FIG. 4, each guide means 4 consists of a first portion of shaft 40, in rotation in a housing 41 provided in the half-shell 20. A crank pin 42 is fixed to one end of the first shaft portion 40, said crank pin carrying a second shaft portion 43 mounted eccentrically relative to the first shaft portion 40. The offset value between the shaft portions 43 and 40 corresponds at the offset value between the drive shaft 17 and the offset bearing 16. The second shaft portion 43 is pivotally mounted in a housing 44 of the central disc 30, a needle bearing 45 ensuring this pivoting. Since the central disc 30 is guided during its orbital movement by the eccentric bearing 16 as well as by the shaft portions 43, that is to say in more than two points, one could have a blockage of the orbital movement or at least a strong wear bearings if the dimensional manufacturing tolerances do not compensate for each other. To overcome this, it is necessary to provide a possibility of adapting the positioning of the central disc 30 relative to the guide means 4. For this purpose, the shaft bearing 43 includes at least one groove 46 in which an elastic O-ring O-Ring type is arranged. Due to the elasticity of the seal (s) 47, the positioning of the central cage 48 of the bearing 45, respectively of the central disc 30 relative to the shaft portion 43, respectively to the half-shell 20 adapts automatically. The device has been described provided with three guide means 4, another number of such means or other means could be provided in order to prevent the rotation of the disc 30 and to allow the described orbital movement.

The embodiment of a spiral vacuum pump described here is only a preferred embodiment, in which the two pairs of spiral walls 27,33 and 28,34 operate in parallel, that is that is to say that the two sets of spirals are identical, being only offset by 180 ° as indicated and that the intake chambers of the two sets of spirals are connected together on the intake port of the pump while the two expulsion chambers of the two sets of spirals are also connected together on the expulsion orifice of the pump. FIG. 2 shows the intake chamber 53 and the expulsion chamber 54 of the set of spirals 28,34. The means to connecting the chambers together and connecting them to their respective orifices are known in the art. Other embodiments are possible, for example a two-stage vacuum pump, where the expulsion chamber of a first set of spirals is connected to the intake chamber of the second set of spirals; in this case, the two sets of spirals are not identical, the second set having a higher compression ratio. One could also have a single set of spiral walls, the fixed portion consisting of a single half-shell and the disc in orbital movement having a single set of spiral wall on only one of its faces. Other constructive provisions than those described may be provided, while meeting the characteristics of the claims.

Claims

1 - Spiral vacuum pump (1) comprising at least

a fixed portion (2) comprising at least one essentially planar wall (25,26) arranged perpendicularly to a longitudinal axis (15) of the pump, a spiral wall (27,28) being arranged perpendicularly projecting on said essentially planar wall ,

a movable portion (3) comprising at least one disc (30) parallel to said essentially flat wall and pivotally mounted on a shaft seat (16) eccentric relative to a drive shaft (17) parallel to said longitudinal axis, guide means (4) imposing an orbital movement of said disc around said eccentric bearing during the rotation of the drive shaft, a spiral wall (33,34) being arranged perpendicularly projecting on at least one essentially flat face (31, 32) of said disc,

the spiral wall (27, 28) of the fixed portion (2) being directed towards said essentially planar face (31, 32) of said disc and the spiral wall (33, 34) of the movable portion (3) being directed towards said essentially planar wall (25, 26) of the fixed portion (2), the two spiral walls having essentially the same shape and being nested one inside the other,

each spiral wall (27, 28, 33, 34) comprising an upper edge (34 A; 52) close to the wall (25, 26) or to the face (31, 32) essentially plane facing it,

characterized in that

a play of small amplitude is arranged between each of said upper edges (34A; 52) and the wall (25, 26) or the essentially planar face (31, 32) facing it. 2- vacuum pump according to claim 1, characterized in that said upper edge is disposed on the upper face (52) of a seal (5) disposed in a housing (34B) arranged on the edge (34A) of said spiral wall

3- Vacuum pump according to claim 1, characterized in that said upper edge is arranged on the upper face of the edge (34A) of said spiral wall.

4- Vacuum pump according to one of the preceding claims, characterized in that the clearance of small amplitude arranged between each of said upper edges (34A; 52) and the wall (25,26) or the face (31, 32) essentially plane facing it is between 0 and 5 hundredths of a mm.

5- vacuum pump according to one of the preceding claims, characterized in that it further comprises means (29) for ensuring a fixed spacing between said essentially planar wall (25,26) of the fixed portion (2 ) and the essentially planar face (31, 32) of the movable portion (3).

6- vacuum pump according to claim 5, characterized in that the means for ensuring a fixed spacing between said essentially planar wall of the fixed portion and the essentially planar face of the movable portion consist of at least one circular shim (29) for axially positioning said fixed portion (21) relative to the frame (13,14) of the pump.

7- Vacuum pump according to one of the preceding claims, characterized in that it further comprises means (19,19A) for axially wedging the movable portion (3.30) in order to prevent any axial movement of said mobile portion.

8- vacuum pump according to claim 7, characterized in that the means for axially wedging the movable portion to prevent any axial movement of said movable portion consist of rolling means (19) and shims (19A) capable of axially fixing said movable portion relative to a bearing surface of the drive shaft (17).

9- Vacuum pump according to one of the preceding claims, characterized in that it further comprises means (60,61, 62,64,65) for statically and dynamically balancing the rotating parts.

10- Vacuum pump according to one of the preceding claims, characterized in that the guide means (4) imposing an orbital movement of said disc (30) around said eccentric bearing (16) during the rotation of the shaft d drive (17) consist of at least a first portion of shaft (40) pivotally mounted in a housing (41) fitted in the fixed portion (2), a pin (42) provided with a second portion d 'shaft (43) being mounted at one end of said first shaft portion, said second shaft portion being offset relative to said first shaft portion of the same value as that of the offset of said disc (30) to the drive shaft (17), said second portion of the shaft being pivotally mounted in a housing (44) arranged in said disc, means (46,47) being provided to compensate for dimensional tolerances for positioning of said disc relative to the fixed portion.

1 1- Vacuum pump according to claim 10, characterized in that said means provided to compensate for dimensional tolerances for positioning of said disc relative to the fixed portion consist of at least one O-ring (47) disposed in a groove (46 ) arranged on the periphery of said second shaft portion (43) introduced into an internal cage (48) of a needle bearing (45).

12- Vacuum pump according to one of the preceding claims, characterized in that the fixed portion (2) comprises two half-shells (20,21) each comprising an essentially planar wall (25,26), a spiral wall ( 27, 28) being arranged perpendicularly on each of the two said essentially flat walls, each of said spiral walls being turned in the direction of the movable portion (3) consisting of a central disc (30) disposed between the two said essentially flat walls (25, 26) and comprising a spiral wall (33, 34) on each of its faces (31, 32), each pair of spiral walls facing each other being nested.

13- Vacuum pump according to claim 12, characterized in that the beginnings of the spirals of the pair of spiral walls (27,33) disposed on one side of the central disc (30) are offset by 180 ° relative to the beginnings of the spirals of the pair of spiral walls (28,34) arranged on the other side of the central disc.

14- Vacuum pump according to one of claims 12 or 13, characterized in that the two sets of spiral walls (27,33,28,34) have the same shape and the same development, the inlet chambers ( 53) of the two said sets of spiral walls being connected, the two outlet chambers (54) of the two said sets of spiral walls also being connected.

AMENDED CLAIMS

[received by the International Bureau on September 02, 1998 (02.09..98); claims let 12-14 replaced by new claims 1 and 12; other changes unchanged (4 pages)]

1- Spiral vacuum pump (1) comprising at least

a fixed portion (2) consisting of two half-shells (20,21) each comprising an essentially planar wall (25,26) arranged perpendicular to a longitudinal axis (15) of the pump, a spiral wall (27,28) being arranged perpendicularly projecting on each of said essentially planar walls,

a movable portion (3) comprising at least one disc (30) parallel to said essentially planar walls and pivotally mounted on a shaft seat (16) eccentric relative to a drive shaft (17) parallel to said longitudinal axis, means guide (4) imposing an orbital movement of said disc around said eccentric bearing during the rotation of the drive shaft, a spiral wall (33,34) being arranged perpendicularly projecting on each of the opposite faces essentially planar ( 31, 32) of said disc,

the spiral wall (27,28) of each of the two half-shells (20,21) of the fixed portion (2) being directed towards said essentially planar face (31,32) which faces it of said disc and the wall in spiral (33,34) of each of the faces (31, 32) of the movable portion (3) being directed towards said essentially flat wall (25,26) of the half-shell (20,21) which faces it from the fixed portion (2), each pair of two corresponding spiral walls (27,33; 28,34) consisting of two spiral walls having essentially the same shape and being nested one inside the other,

each spiral wall (27,28,33,34) comprising an upper edge (34A; 52) close to the wall (25,26) or to the face (31, 32) essentially planar facing it, a play of weak amplitude being arranged between each of said upper edges (34A; 52) and the wall (25,26) or the essentially planar face (31,32) facing it,

characterized in that the beginnings of the spirals of the pair of spiral walls (27,33) arranged on one side of the central disc (30) are offset by 180 ° relative to the beginnings of the spirals of the pair of spiral walls (28,34) arranged on the other side of the central disc.

2- vacuum pump according to claim 1, characterized in that said upper edge is disposed on the upper face (52) of a seal (5) disposed in a housing (34B) arranged on the edge (34A) of said spiral wall

5- vacuum pump according to one of the preceding claims, characterized in that it further comprises means (29) for ensuring a fixed spacing between said essentially planar walls (25,26) of the fixed portion (2 ) and said essentially planar faces (31, 32) of the movable portion (3).

6- vacuum pump according to claim 5, characterized in that the means for ensuring a fixed spacing between said essentially planar wall of the fixed portion and said essentially planar faces of the movable portion consist of at least one circular shim (29) for axially positioning said fixed portion (21) relative to the frame (13,14) of the pump.

7- Vacuum pump according to one of the preceding claims, characterized in that it further comprises means (19.19A) allowing axially wedging the movable portion (3.30) in order to prevent any axial movement of said movable portion.

8- vacuum pump according to claim 7, characterized in that the means for axially wedging the movable portion to prevent any axial movement of said movable portion consist of rolling means (19) and shims (19A) suitable axially fixing said movable portion relative to a bearing surface of the drive shaft (17).

11 - Vacuum pump according to claim 10, characterized in that said means provided to compensate for dimensional tolerances for positioning of said disc relative to the fixed portion consist of at least one O-ring (47) disposed in a groove (46) fitted around the periphery of said second shaft portion (43) introduced into an internal cage (48) of a needle bearing (45). 12- Vacuum pump according to one of the preceding claims, characterized in that the two sets of spiral walls (27,33,28,34) have the same shape and the same development, the inlet chambers (53) two said sets of spiral walls being connected, the two outlet chambers (54) of the two said sets of spiral walls also being connected.

DECLARATION ACCORDING TO ARTICLE 19

Claim 1 has been amended as follows:

- The characterizing part of initial claim 1 has been introduced in the preamble;

- The characterizing part of initial claim 12 has been introduced in the preamble;

- The characterizing part consists of the characterizing part of the old claim 13.