SIDE CHANNEL COMPRESSOR

BACKGROUND OF THE INVENTION

Field of the Invention

The invention concerns a side channel compressor for compressing a gas. The invention therefore concerns a work machine for compressing gases, such as air or technical gases.

Background Art

The operation of the side channel compressor results in a broadband sound spectrum. In conventional side channel compressors, tonal sound compo- nents occur at certain frequencies of the side channel compressor which are extremely annoying if they differ from the broadband sound spectrum by more than 7 dB.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a side channel compressor which ensures a particularly silent operation.

This object is achieved by a side channel compressor for compressing a gas the side channel compressor comprising a housing; a side channel located in the housing for compressing a gas; a gas inlet opening formed in the housing which is in flow connection with the side channel for introducing a gas to be compressed; a gas outlet opening formed in the housing for discharging the gas to be compressed from the side channel, the gas outlet

opening being in flow connection with the gas inlet opening by way of the side channel; and an impeller which is mounted for rotary drive in the housing and has at least two impeller blades disposed in the side channel, wherein at least one impeller blade has at least one flow recess in its free edge region. The essence of the invention is that at least one flow recess is provided in the free edge region of at least one impeller blade of the side channel compressor. The free edge region is the region which is located in the side channel and which may be surrounded by the gas to be compressed. The at least one flow recess or the amount of gas flowing through this flow recess, respectively, reduces gas turbulence structures and/or periodic gas flow structures occurring at the trailing side of the impeller blades. This ensures a particularly silent operation of the side channel compressor.

The following is a detailed description of several preferred embodiments of the invention by means of the enclosed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a side view of a side channel compressor and of a drive flange-mounted to the side channel compressor, the Figure showing a partial longitudinal sectional view of the side channel compressor;

Fig. 2 shows a front elevation view of the side channel compressor shown in Fig. 1 ;

Fig. 3 shows a front elevation view of the side channel compressor shown in Fig. 2 with its housing cover taken off;

Fig. 4 shows a schematic view of an inventive impeller according to a first embodiment of a side channel compressor;

Fig. 5 shows a substantially rear view of an impeller blade of the impeller shown in Fig. 4;

Fig. 6 shows a schematic view of an inventive impeller according to a second embodiment;

Fig. 7 shows a substantially rear view of an impeller blade of the impeller shown in Fig. 6;

Fig. 8 shows a schematic view of an inventive impeller according to a third embodiment;

Fig. 9 shows a substantially rear view of an impeller blade of the impeller shown in Fig. 8;

Fig. 10 shows a schematic view of an inventive impeller according to a fourth embodiment;

Fig. 1 1 shows a substantially rear view of an impeller blade of the impeller shown in Fig. 10;

Fig. 12 shows a schematic view of an inventive impeller according to a fifth embodiment;

Fig. 13 shows a substantially rear view of an impeller blade of the impeller shown in Fig. 12;

Fig. 14 shows a schematic view of an inventive impeller according to a sixth embodiment;

Fig. 15 shows a substantially rear view of an impeller blade of the impeller shown in Fig. 14;

Fig. 16 shows a schematic view of an inventive impeller according to a seventh embodiment;

Fig. 17 shows a substantially rear view of an impeller blade of the impeller shown in Fig. 16; and

Fig. 18 shows a schematic view of an inventive impeller according to an eighth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A side channel compressor shown in Figs. 1 to 3 for compressing a gas comprises an impeller 2 which is provided with impeller blades 1 and is mounted in a housing 3 for rotation about a horizontal central longitudinal axis 4. A conventional drive 6 serves for rotary drive of the impeller 2 in the direction of the arrow 5. The gas is thus transported through the housing 3 in the direction of the arrow 5 as well.

The housing 3 comprises a housing body 7 and a demountable housing cover 8 which are joined together according to Figs. 1 and 2 so as to en-

close the impeller 2 comprising the impeller blades 1 which is drivable for rotation and is disposed on a drive shaft 9 for co-rotation therewith.

The impeller 2 is provided with a single blade ring and is designed like a disk. The impeller 2 comprises an inner impeller hub 10 with a central circular hub bore 11. The impeller hub 10 is formed by an inner hub foot 12 which radially outwardly delimits the hub bore 11 , and by a radial circular hub washer 13 adjoining the hub foot 12. Moreover, the impeller 2 comprises a radial outer carrier ring 14 which adjoins the outside of the hub washer 13 and overlaps with both sides of said hub washer 13 in the direction of the central longitudinal axis 4. The carrier ring 14 carries a multitude of radially projecting impeller blades 1 which are distributed in the circumferential direction. In this embodiment, a total of 52 individual impeller blades 1 are provided which are preferably arranged equidistantly so as to have an angular distance from one another, relative to the central longitudinal axis 4, that amounts to approximately 7°. Thus, 6 to 7 impeller blades 1 are disposed at every 45°. The hub foot 12, the hub washer 13 and the carrier ring 14 form an integral cast part.

The terms "axial" and "radial" used in-here are relative to the central longitudinal axis 4. The terms "inner" and "outer" are relative to the central longitudinal axis 4 as well. The term "inner" means that an inner region is nearer to the central longitudinal axis 4 than an outer region.

The central hub bore 11 may receive the drive shaft 9. A conventional parallel-key connection is provided between the drive shaft 9 and the hub foot 12 so as to transmit the torque generated by the drive shaft 9 to the impeller hub 10 for rotating the impeller 2.

The housing body 7 comprises a central hub portion 15 which radially and axially delimits a partial hub receiving space 16. A central shaft bore 17 passes through the hub portion 15 and opens into the partial hub receiving space 16. An annular side wall 18 adjoins the hub portion 15, said annular side wall 18 extending radially outwardly from the hub portion 15. A circumferential channel portion 19 adjoins the outside of the side wall 18. The hub portion 15, the side wall 18 and the channel portion 19 form an integral cast part which forms the housing body 7. Rib webs 20 extending in a spoke-like manner are provided on the outside of the housing body 7 which considerably increase the stability of the housing body 7. Moreover, screw bosses 21 project radially outwardly from the side wall 18.

The housing cover 8 is secured to the housing body 7 by means of several connecting screws 22 and comprises a central hub portion 23 which ra- dially and axially delimits a partial hub receiving space 24. A radially outwardly extending annular side wall 25 adjoins the hub portion 23. A circumferential channel portion 26 is attached to the outside of the side wall 25. A rolling-element bearing 27 for the drive shaft 9 is disposed in the hub portion 23. The hub portion 23, the side wall 25 and the channel portion 26 form an integral cast part which forms the housing cover 8. Likewise, rib webs 28 extending in a spoke-like manner also project from the outside of the side wall 25 so as to reinforce the housing cover 8.

The housing body 7 and the housing cover 8 are joined together such that the two partial hub receiving spaces 16, 24 define a hub receiving space 29 between each other, and the two channel portions 19, 26 define a side channel 30 between each other for compression of the gas. The two side walls 18, 25 are parallel but spaced from one another. The side channel 30, which is spaced from the central longitudinal axis 4, extends annularly

about the central longitudinal axis 4 and is delimited by the channel portions 19, 26.

An axial gas inlet opening 31 projecting into the side channel 30 is formed at the bottom of the housing cover 8. Further provided at the bottom of the housing cover 8 is an axial gas outlet opening 32 which is in flow connection with the side channel 30 as well and is adjacent to the gas inlet opening 31. A projecting gas inlet connector 33 is connected to the gas inlet opening 31 while a gas outlet connector 34 projecting in a likewise manner is connected to the gas outlet opening 32. An interceptor 35 is disposed in the side channel 30 between the gas inlet opening 31 and the gas outlet opening 32.

The hub foot 12 of the impeller 2 is disposed in the hub receiving space 29 defined by the hub portions 15, 23, with the drive shaft 9 passing through the hub bore 17. The drive shaft 9 is provided with a free bearing journal 36 at its end which is mounted for rotation in the rolling element bearing 27 in the housing cover 8. The rolling element bearing 27 is provided with an inner ring 37 connected to the bearing journal 36 and an outer ring 38 connected to the housing cover 8, with the rings being separated by rolling elements - in the shape of bearing balls 39 - disposed therebetween. The inner ring 37 is shrunk onto the bearing journal 36 for co-rotation therewith while the outer ring 38 is attached to the housing cover 8 in a non- rotational manner. The hub washer 13 of the impeller 2 extends radially outwardly from the hub foot 12 between the spaced-apart side walls 18, 25 of the housing 3. The carrier ring 14 and the impeller blades 1 are located in the circumferential side channel 30. A certain portion of the foot of the carrier ring 14 is positioned in an outwardly open recess 40 which is formed in the channel portions 19, 26 next to the side walls 18, 25.

The side channel 30 has a free cross-sectional area which is available for transporting the gas and is approximately perpendicular to the arrow 5. Said cross-sectional area tapers from a cross-sectional area A _E at the gas inlet opening 31 to a cross-sectional area A ^ at the gas outlet opening 32 such that A _A < A _E . The side channel 30 may however have a constant cross-sectional area as well.

The side channel 30 has a radial height S. The drive 6 is an electric motor which is detachably connected to the outside of the housing body 7. To this end, several fastening screws are provided which are screwed in the screw bosses 21 at the housing body 7.

In order to ensure that the unit formed by the side channel compressor and the drive 6 is securely installed, support feet 41 are formed at the bottom of the side channel compressor while support feet 43 are formed at the bottom of a carrier body 42 as well, wherein the carrier body 42 is connected to the housing body 7 by means of screws and carries the drive 6.

A vertical plane E runs through the central longitudinal axis 4 and inter- sects the side channel compressor in a vertically symmetrical manner or centrally along the length, respectively.

The impeller blades 1 according to a first embodiment are now described in more detail by means of Figs. 4 and 5. Each impeller blade 1 is substan- tially designed like a plate and has a substantially rectangular shape with a corresponding contour. The impeller blades 1 are designed identically and symmetrically relative to a symmetry plane X which is oriented perpendicular relative to the vertical plane E and runs through the center of the

hub washer 13. Each impeller blade 1 further has an edge which is composed of a radially outer edge region 45, a radially inner edge region 46 opposite thereto, and lateral edge regions 47 inter-connecting the outer and inner edge regions. The inner edge region 46 is in direct connection with the carrier ring 14 and may also be regarded as the foot area of the impeller blade 1 while the entire edge region 45 - which may be regarded as the head area of the impeller blade 1 - is entirely located in the side channel 30 and is oriented substantially parallel to the central longitudinal axis 4. The lateral edge regions 47 are substantially parallel to each other and extend substantially radially outwardly from the inner edge region 46. The edge regions 45 and 47 are free, in other words there are no adjacent elements whatsoever. The inner edge region 46, on the other hand, is not free as it is adjoined by the carrier ring 14. The edge regions 45, 46, 47 define a front surface 48 facing in the direction of the arrow 5 and a rear surface 49 oppo- site thereto, thus facing in the opposite direction of the arrow 5. Each impeller blade 1 further comprises an inner edge portion 50 adjoining the inner edge region 46 and an outer edge portion 51 adjoining the outer edge region 45. The inner edge portion 50 extends radially outwardly from the inner edge region 46, while the outer edge portion 51 is slightly inclined forwardly in the direction of the arrow 5 relative to the inner edge portion 50 for reasons of flow. The outer edge portion 51 also reduces in thickness towards the outer edge region 45 when seen in the circumferential direction.

The distance between the outer edge region 45 and the inner edge region 46 defines a radial height H of an impeller blade 1, wherein the radial height H of the inner edge portion 50 preferably amounts to between 55% and 75% of the radial height H. The radial height H is present near the lateral edge

regions 47. Furthermore, each impeller blade 1 has an axial width B which is defined by the distances between the opposite edge regions 47.

The radial height H of an impeller blade 1 is smaller than the radial depth S of the side channel 30. The radial height H amounts to between approximately 50% and 75%, preferably to approximately 60%, of the radial depth S of the side channel 30. Moreover, the axial width B of an impeller blade 1 is always considerably smaller than the corresponding axial width of the side channel 30.

In this embodiment, the lateral edge regions 47 of an impeller blade 1 are in each case further equipped with a reduction groove 52 having a substantially rectangular cross-section, wherein said reduction groove 52 is axially outwardly open and is parallel to the outer edge region 45. These reduction grooves 52 are not shown in Figs. 1 to 3. Each reduction groove 52 opens into the corresponding front surface 48 and rear surface 49 of an impeller blade 1, thus passing through the entire outer lateral side of the impeller blade 1. The opposite reduction grooves 52 are on a common level in the inner edge portion 50. They are located in the lower half of the inner edge portion 50 at a distance from the inner edge region 46, with each of the reduction grooves having a radial height A which amounts to between approximately 5% and 20%, preferably to between 10% and 15% of the radial height H of an impeller blade 1. The axial depth T of a reduction groove 52 amounts to between approximately 2% and 12%, preferably to between 5% and 9%, of the axial width B of an impeller blade 1.

The following is a description of an inventive side channel compressor. The drive shaft 9 is set in rotation about the central longitudinal axis 4 in the direction of the arrow 5 by means of the drive 6. As it is coupled to the

drive shaft 9 for co-rotation therewith, the impeller 2 comprising the impeller blades 1 therefore starts to rotate in the direction of the arrow 5 as well. Passing close to the gas inlet opening 31, the impeller blades 1 draw the gas to be compressed into side channel 30 through the gas inlet connector 33 and the gas inlet opening 31. The gas located in the side channel 30 is accelerated, by means of the impeller blades 1, in the direction of the arrow 5 which may thus also be referred to as transport arrow. The front surfaces 48 of the impeller blades 1 face forwardly in the direction of the arrow 5 and serve for the transport of the gas located in the side channel 30. During the transport, the gas is virtually trapped in cells 44 which are inwardly delimited by the carrier ring 14 and by adjacent impeller blades 1 in the circumferential direction. A cell 44 is in particular defined by the front surface 48 of an impeller blade 1 and the rear surface 49 of an impeller blade disposed adjacent thereto. The edge regions 45, 47 are free, thus allowing the gas to flow across or to pass by, respectively.

Due to the reduction grooves 52, the respective surface area of the front surfaces 48 and rear surfaces 49 of the impeller blades 1 is smaller than that of conventional ungrooved impeller blades. The reduction grooves 52 form flow channels, enabling a part of the gas to pass from one cell into another, downstream cell 44 which is located in the opposite direction of the arrow 5. The reduction grooves 52 thus also act as lateral flow grooves through which a part of the gas can flow. These reduction grooves 52, or the amount of gas flowing through these reduction grooves 52, respec- tively, lead to a reduction of gas turbulence structures at the trailing side of the impeller blades 1. This in particular reduces the magnitude and intensity of the gas turbulence structures in the side channel 30 and consequently leads to a reduction of pressure variations. The operating noise of the side channel compressor is reduced as well. At the end of the circula-

tion zone, the compressed gas is discharged from the side channel 30 via the gas outlet opening 32 and the gas outlet connector 34 by way of the impeller blades 1. The angular path covered by the gas in the side channel compressor amounts to approximately 300°. The interceptor prevents the gas transported by the impeller 2 from being carried over from the gas outlet opening 32 to the gas inlet opening 31 in the side channel 30.

The following is a description of a second embodiment of the invention by means of Figs. 6 and 7. Identical parts are referred to with the same refer- ence numerals as the first embodiment shown in Figs. 4 and 5 to the description of which reference is made. Parts that are different in design but have the same function are denoted by the same reference numerals with a subsequent a. The impeller 2a shown in Fig. 6 differs from the impeller 1 shown in Fig. 4 with respect to its impeller blades Ia which are again symmetrical relative to the symmetry plane X. Unlike the impeller blades 1 according to Figs. 4 and 5, the impeller blades Ia are provided with two spaced-apart, identical reduction grooves 52 in each edge region 47a, said reduction grooves 52 being parallel to each other and to the outer edge region 45. The reduction grooves 52 are in each case located in the inner edge portion 50 and are disposed one above the other. They pass through the entire impeller blade 1 again, thus virtually forming flow channels. The lower reduction groove 52 is disposed at a distance from the lower edge region 46 while the upper reduction groove 52 is disposed at a distance from the edge portion 51. As far as design, dimension and function of the reduction grooves 52 are concerned, reference is made to the aforementioned embodiment. Compared to the aforementioned embodiment, i.e. compared to the impeller blades 1 according to the first embodiment, the surfaces 48a, 49a of the impeller blades Ia are even smaller, and due to the doubling of the reduction grooves 52, approximately twice the amount of

gas is able to flow from cell 44 to cell 44. The gas turbulence structures at the trailing side are reduced even more.

The following is a description of a third embodiment of the invention by means of Figs. 8 and 9. Identical parts are referred to with the same reference numerals as the second embodiment shown in Figs. 6 and 7 to the description of which reference is made. Parts that are different in design but have the same function are denoted by the same reference numerals with a subsequent b. Unlike the aforementioned embodiment shown in Figs. 6 and 7, this embodiment is provided with a reduction groove 52 in the outer edge portion 51b as well. Each edge region 47b is provided with a total of three identical reduction grooves 52 which are in each case spaced from each other. They are parallel to each other and to the outer edge region 45. The upper reduction groove 52 in the edge portion 5 Ib is disposed at a dis- tance from the outer edge region 45. The reduction grooves 52 are disposed one above the other at identical distances relative to each other. The impeller blades Ib are again symmetrical relative to the symmetry plane X. As far as dimensioning, design and function of the reduction grooves 52 are concerned, reference is made to the aforementioned embodiment. Com- pared to the second embodiment, turbulence structures at the trailing side are reduced even more as the additional reduction grooves 52 make the surfaces 48b, 49b even smaller, thus enabling more gas to flow through the reduction grooves 52.

The following is a description of a fourth embodiment of the invention by means of Figs. 10 and 11. Identical parts are referred to with the same reference numerals as the third embodiment shown in Figs. 8 and 9 to the description of which reference is made. Parts that are different in design but have the same function are denoted by the same reference numerals with a

subsequent c. The only difference to the third embodiment according to the Figs. 8 and 9 is that the reduction grooves 52c have a semi-circular cross- section instead of a rectangular one. They are again axially outwardly open and pass through the entire impeller blades Ic. They are disposed one above the other and have a maximum depth that is equal to depth T. Their maximum outside height is approximately equal to height A. As far as position and function of the reduction grooves 52c are concerned, reference is made to the third embodiment. In this embodiment, the impeller blades Ic are subject to a particularly low notch effect. Semi-circular reduction grooves 52c are also suitable for the first and second embodiments.

The following is a description of a fifth embodiment of the invention by means of Figs. 12 and 13. Identical parts are referred to with the same reference numerals as the first embodiment shown in Figs. 4 and 5 to the de- scription of which reference is made. Parts that are different in design but have the same function are denoted by the same reference numerals with a subsequent d. Unlike the first embodiment shown in Figs. 4 and 5, the lateral edge regions 47d are not provided with reduction grooves. Instead, the outer edge region 45d is provided with four spaced-apart, identical reduc- tion grooves 52 that pass through the entire impeller blade Id and are disposed next to each other. In this embodiment, the reduction grooves 52, which form flow channels, are located in the outer edge portion 51 only and have a radial depth that is substantially equal to depth T. Their width is also substantially equal to height A so that the cross-sectional area of a re- duction groove 52 is thus equal to the cross-sectional area of a reduction groove 52 shown in Figs. 4 and 5. The reduction grooves 52 have a rectangular cross-section and are radially outwardly open. They have an identical distance from each other. The impeller blades Id are designed symmetrically relative to the plane X. This design reduces gas turbulence structures

at the trailing side as well. As far as dimensioning and shape of the reduction grooves 52 are concerned, reference is made to the first embodiment. Instead of the four reduction grooves 52, only one central reduction groove 52 may be provided. However, each impeller blade Id may also be pro- vided with two or three or even more reduction grooves 52, which should then also be disposed in a preferably symmetrical manner. Instead of the rectangular shape shown here, other shapes are applicable as well, such as a semi-circular shape.

The following is a description of a sixth embodiment of the invention by means of Figs. 14 and 15. Identical parts are referred to with the same reference numerals as the third or fifth embodiments, respectively, shown in Figs. 8 and 9 as well as Figs. 12 and 13 to the description of which reference is made. Parts that are different in design but have the same function are denoted by the same reference numerals with a subsequent e. This impeller 2e has impeller blades Ie which are substantially a combination of the impeller blades Ib and Id shown in Figs. 8, 9 and 12, 13. In this embodiment, each impeller blade Ie has three spaced-apart reduction grooves 52 disposed one above the other in each lateral edge region 47b and four spaced-apart reduction grooves 52 disposed in succession in the radial outer edge region 45d of the impeller blade. As far as dimensioning, position and shape of the reduction grooves 52 are concerned, reference is made to the first, third and fifth embodiments. In this embodiment, each of the free edge regions 45d, 47b is thus provided with grooves, which results in a particularly low turbulence structure at the trailing side since a particularly high number of reduction grooves 52 is provided and the surfaces 48e, 49e are particularly small. The impeller blades Ie are again symmetrical relative to the symmetry plane X. Alternatively, the semi-circular reduction grooves 52c are also applicable in this embodiment. Furthermore, each of

the edge regions 45d and/or 47b may be provided with a different number of reduction grooves 52.

An axially lateral and/or radially outer grooving of the impeller blades re- duces the front and rear surfaces thereof by forming flow channels, thus reducing turbulence structures at the trailing side. The reduction grooves may be of any desired shape. To this end, each impeller blade is provided with at least one reduction groove. Each of the lateral edge regions and/or the radially outer edge regions may be provided with any desired number of grooves. One and the same impeller blade may also be provided with reduction grooves of different shapes. Each lateral edge region and/or each outer edge region is provided with at least one reduction groove, wherein the actual number of which in the respective edge regions may be randomly selected and may be different from one edge region to the next. A symmetrical design of the impeller blades or a symmetrical arrangement of the reduction grooves, respectively, is preferred.

As an alternative to the described grooves, the lateral edge regions can also be chamfered, in other words they can have set-back blade edges, and/or the radially outer edge regions can be chamfered as well. These chamfers form flow recesses again that reduce the front and/or rear surfaces of the impeller blades so that turbulence structures at the trailing side are reduced to a minimum. The lateral flow recesses may be oriented such that the impeller blades become larger or smaller from their front surfaces towards their rear surfaces. The impeller blades or lateral edge regions, respectively, may also converge upwardly or radially outwardly, respectively, such that the outer edge portion has a substantially trapezoidal shape, for instance. In that case, flow recesses are thus provided both radially and laterally.

The following is a description of a seventh embodiment of the invention by means of Figs. 16 and 17. Identical parts are referred to with the same reference numerals as the first embodiment to the description of which reference is made. Parts that are different in design but have the same function are denoted by the same reference numerals with a subsequent f. In all aforementioned embodiments, the impeller 2 has a single blade ring. In this embodiment on the other hand, the impeller 2f is configured as a double blade ring with another, outer carrier ring 53 which delimits the cells 44 radially outwardly and adjoins the outer edge region 45f of the impeller blades If. Otherwise, there are no major differences compared to the first embodiment. The individual impeller blades 2f are again symmetrical relative to a symmetry plane X. As in the first embodiment, each edge region 47f of this embodiment is provided with a reduction groove 52. The reduction grooves 52 are adjacent to the corresponding edge region 46f. As far as shape, dimensioning and position of said reduction grooves 52 are concerned, reference is made to the first embodiment. According to alternative embodiments, each of the lateral edge regions 47f is provided with more than one reduction groove 52. Alternatively, the reduction grooves 52 are again so designed as to have a different, for instance a semi-circular, cross- section. Again, other recesses, such as chamfers, in the edge regions 47f are conceivable as well.

The following is a description of an eighth embodiment of the invention by means of Fig 18. Identical parts are referred to with the same reference numerals as the embodiment shown in Figs. 4 and 5 to the description of which reference is made. Unlike the first embodiment, not all of the impeller blades 1 of this embodiment are grooved in the lateral edge regions 47 but only 30% to 70%, preferably 40% to 60%, of all impeller blades. In this embodiment, impeller blades 1 with reduction grooves 52 according to the

first embodiment are disposed between impeller blades without reduction grooves. The grooved impeller blades 1 are disposed randomly, i.e. stochastically. As shown at the top of Fig. 18, three regular, i.e. ungrooved impeller blades are provided between two grooved impeller blades 1. At the upper lateral sides on the other hand, only two regular impeller blades are provided between two grooved impeller blades 1. It is however also conceivable to arrange two grooved impeller blades 1 directly behind each other. In this embodiment, the reduction grooves 52 act as reducing grooves for reducing periodic flow structures. This prevents formation of regular, harmonic flow structures, thus ensuring a particularly silent operation of the side channel compressor. Again, the gas turbulence structures at the trailing side are reduced as well.

Instead of the impeller blades 1 described here according to the embodi- ment shown in Figs. 4 and 5, the other aforementioned impeller blades are applicable as well. Also, several different impeller blades of the aforementioned embodiments may be provided in one and the same impeller. Sequence repetitions are possible. Alternatively, identically grooved impeller blades may be provided several times in a row. The sequence is thus com- pletely random. What is essential is that the impeller blades are designed differently, for instance in terms of their shape and/or size. The impeller blades can also only differ in height and/or width. They are preferably disposed equidistantly.

The side channel compressor may comprise at least one stationary projection for engaging with the at least one flow recess or reduction groove 52, 52c. In contrast to the at least one movable flow recess or reduction groove 52, 52c, the at least one projection is immobile.

The interceptor 35 for the impeller 2, 2a, 2b, 2c, 2e, 2f may have at least one projection which projects towards the impeller 2, 2a, 2b, 2c, 2e, 2f and may engage with the at least one flow recess or reduction groove 52, 52c in the lateral edges 47, 47a, 47b, 47c, 47f of the impeller blades 1, Ia, Ib, Ic, Ie, If. One projection of the interceptor 35 is provided for each flow recess or reduction groove 52, 52c. The interceptor 35 for the impeller 2 has one projection. The interceptor 35 for the impeller 2a has two separate projections. The interceptors 35 for the impellers 2b, 2c and 2e have three separate projections. The interceptor for the impeller 2f has one projection. The size and the design of the projections are adapted to the size and the design of the flow recesses or reduction grooves 52, 52c. There is a small play between the at least one projection and the at least one flow recess or reduction groove 52, 52c. The at least one projection counteracts with a pressure release.

According to a further embodiment, there is at least one projection on the housing 3 which projects towards the impeller 2, 2a, 2b, 2c, 2d, 2e, 2f and may engage with the at least one flow recess or reduction groove 52, 52c. The at least one projection may engage with the flow recesses or reduction grooves 52, 52c in the lateral edges 47, 47a, 47b, 47c, 47f and/or in the head edges 45, 45d. The size and the design of the at least one projection is adapted to the size and the design of the flow recesses or reduction grooves 52, 52c.

The at least one projection may have an elongate curved form which is concentric to the longitudinal axis 4.