Three-stage screw compressor

Abstract

A multi-staged screw compressor system includes a gearbox, a drive gear located in the gearbox, and a first, second and third screw compressor that are fastened to the gearbox and coupled to the drive gear such that the first, second, and third screw compressors are all driven in common by the drive gear. During operation the first screw compressor compresses a flow of gaseous fluid from an inlet pressure to a first intermediate pressure, the second screw compressor compresses the flow of fluid from the first intermediate pressure to a second intermediate pressure, and the third screw compressor compresses the flow of fluid from the second intermediate pressure to a final pressure. The final pressure is at least thirty times the inlet pressure.

Description

BACKGROUND

The invention pertains to a multi-stage screw compressor system. Preferably, the screw compressor system is a “dry-running” system for high pressures, typically 40 bar and above. A preferred area of applicability is the production of compressed air for blow-molding of plastic bottles.

A two-stage screw compressor system is known from U.S. Pat. No. 3,407,996 (corresponding to DE-A-1628201). It has a gearbox with a perpendicular mounting wall, attached to which are two adjacent compressor stages that cantilever parallel with one another. Each compressor stage comprises a screw compressor with two mutually engaging screw rotors. Located in the gearbox is a transmission with a drive gear that meshes with two driven gears that rotate the rotors of the two screw compressors. Also disclosed in the document is that the invention described in it can also be used in multistage compressor systems with more than two stages. However, there is no indication of how further compressor stages can be arranged, and the design that is described in detail has no place for further compressor stages.

A similar two-stage screw compressor system is also known from DE 299 22 878.9 U1.

The object of the invention is to design a three-stage screw compressor system that can deliver a compressed gaseous fluid, in particular compressed air, at a very high pressure, typically about 40 bar and above, and that is characterized by its space-saving design, its simplicity and robustness. In another embodiment of the invention, the three-stage screw compressor system according to the invention allows the ratio of the RPM's of the three compressor stages to be changed in a simple manner.

The screw compressor system according to the invention can compress gaseous fluid, in particular air, to a very high pressure ratio, for example 40:1, using only three compressor stages; thus, compressed air can be supplied at a high pressure as is required for industrial manufacturing processes such as blow-molding of plastic bottles.

In the screw compressor system according to the invention, the screw compressors that constitute the first and second stages are located above the horizontal plane that runs through the rotating axis of the drive gear, whereas the screw compressor of the third stage is located below the screw compressors of the first and second stages and below the horizontal plane running through the rotating axis of the drive gear, and whereas its driven gear meshes with the drive gear near its lowest point. This results in an especially advantageous utilization of the existing space configurations and thus a space-saving, compact design of the compressor system. By using different exchangeable bearings and flange parts, the position of the drive shaft can be changed in the horizontal direction and the position of the third compressor stage can be changed in the vertical direction in order to adjust the gearing configuration to different diameters of gears and thus to different RPM ratios of the compressor stages.

SUMMARY

In one construction, the invention provides a multi-staged screw compressor system with a gearbox (90), a drive gear (95) located in the gearbox, and a first, second and third screw compressor (60, 70, 80) that are fastened to the gearbox and coupled to the drive gear such that they are all driven in common by the drive gear. During operation, the first screw compressor (60) compresses a flow of gaseous fluid from an inlet pressure to a first intermediate pressure, the second screw compressor (70) compresses the flow of fluid from the first intermediate pressure to a second intermediate pressure, and the third screw compressor compresses the flow of fluid from the second intermediate pressure to a final pressure, wherein the final pressure is at least thirty times, preferably at least forty times the inlet pressure.

In another construction, a multistage screw compressor system consists of a gearbox (9)0, to which a first, second and third screw compressor (60, 70, 80) are attached in parallel and cantilevered, and which are driven in common by a drive gear in the gearbox. A gaseous fluid is compressed by the first screw compressor (60) to a first intermediate pressure of about 3.5 bar, by a second screw compressor (70) to a second intermediate pressure of about 12 bar and by the third screw compressor (80) to an internal pressure of about 40 bar. Driven gears (65, 75) of the first and second screw compressors mesh with the drive gear (95) above its axis, whereas the driven gear (85) of the third screw compressor (80) meshes with the drive gear (95) near its lowest point T. The position of the axis of the drive gear (95) is able to be changed in the horizontal direction and the position of the driven gear (85) of the third screw compressor (80) is able to be changed in the vertical direction for the capability of installing gear sets with different diameter ratios.

In another construction, the invention provides a multi-staged screw compressor system that includes a gearbox including a housing having a mounting wall. A drive gear is supported by the housing for rotation about a drive axis. The drive axis divides the drive gear into a first upper quadrant, a second upper quadrant, a first lower quadrant, and a second lower quadrant, each quadrant extending between a vertical plane and a horizontal plane that intersect on the drive axis. A first mating flange, a second mating flange, and a third mating flange are each formed as part of the mounting wall to define three substantially planar surfaces arranged normal to the drive axis. A low pressure screw compressor is coupled to the first mating flange and includes a first driven gear, the first driven gear disposed completely within the first upper quadrant. A middle pressure screw compressor is coupled to the second mating flange and includes a second driven gear, the second driven gear disposed completely within the second upper quadrant. A high pressure screw compressor is coupled to the third mating flange and includes a third driven gear, the third driven gear disposed within at least one of the first lower quadrant and the second lower quadrant. The low pressure screw compressor, the middle pressure screw compressor, and the high pressure screw compressor cooperate to compress a gas from a first pressure to a second pressure that is at least 30 times the first pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention is explained in more detail with the help of the drawings. Shown are:

FIG. 1 a perspective view of three-stage compressor system according to an embodiment of the invention;

FIG. 2 a perspective, partial sectional view of the screw compressor that constitutes the third stage of the compressor system according to FIG. 1;

FIG. 3 a perspective, partial sectional view of the gearbox and transmission of the compressor system according to FIG. 1, with the compressor stages left out;

FIG. 4 a simplified representation of the gears that make up the transmission of the compressor system;

FIG. 5 a view of the mounting wall of the gearbox, partially removed in order to make the transmission visible.

DETAILED DESCRIPTION

FIG. 1 shows a perspective view of a three-stage screw compressor system with three screw compressors 60, 70, 80 that are attached to a gearbox 90 via flanges, said gearbox having essentially the shape of a perpendicular plate, and said screw compressors cantilevered parallel to one another. To accomplish this, the housing of each screw compressor 60, 70, 80 has a flange 64, 74 and 84 at its end facing the gearbox 90, said flange being connected to an associated mating flange on the gearbox 90. The three screw compressors 60, 70, 80 are driven by a common motor-driven drive gear held in the gearbox 90; this arrangement will be explained in more detail below. In the compressor system shown, screw compressor 60 is the initial stage (low pressure stage), with inlet opening 61 and outlet opening 63, screw compressor 70 is the second or intermediate stage with inlet opening 71 and outlet opening 73, and screw compressor 80 is the final stage (or high pressure stage) with inlet opening 81 and an outlet opening on the side opposite the inlet opening 81 that is not shown in FIG. 1. FIG. 1 also shows an oil sump housing 76 that is flanged to the base of the gearbox 90 and that is connected to the synchronizing gears of screw compressors 60, 70, 80 and to the drive gear located in the gearbox 90.

Not shown in FIG. 1 are the connection lines for the medium to be compressed, in particular air, which connect the inlets and outlets of the three screw compressors 60, 70, 80. These lines are designed in a manner known to those trained in the art and can be equipped with filters, intercoolers, and/or mufflers, for example.

The screw compressors 60, 70 of the first and second stage are located next to one another horizontally, whereas screw compressor 80, the third stage, is located beneath the screw compressors of the first and second stage. The oil sump housing 76 has a recess 79 on its upper surface that creates additional space with which to hold the screw compressor of the third stage.

Each of the three screw compressors 60, 70, 80 of FIG. 1 has two rotors, in the usual fashion, that are rotatably held in a rotor housing with parallel axes and that mesh with one another with screw-shaped ribs and grooves. For example, FIG. 2 shows screw compressor 80, which constitutes the third stage of the three-stage compressor system of FIG. 1, said compressor being especially designed for high pressures of preferably about 40 bar and above.

The screw compressor shown in FIG. 2 has a rotor housing 1 (shown in a longitudinal section) in which two rotors 3 and 5 are rotatably held with parallel axes. The rotating axes of the rotors 3, 5 lie in a common vertical plane. Each rotor 3, 5 has a profile section 7 and 9 with a profile that contains screw-shaped ribs and grooves, wherein the ribs and grooves of the two profile sections 7, 9 mesh with one another to form a seal. On both sides of the profile sections 7, 9 are shaft pins 7a, 7b, 9a, 9b, the surfaces of which cooperate with seal arrangements 11, 12 to seal the rotor in the rotor housing 1. The shaft pins 7a, 7b, 9a, 9b are also rotatably held in the rotor housing 1 with bearings 13, 15.

The upper rotor 3 in FIG. 2 is the main rotor, at the left end of which in FIG. 2 is an extended shaft pin 7c that extends into the gearbox 90 (FIG. 1) and supports a gear 85 that meshes with a drive gear in the gearbox in order to turn the rotor 3. At the right end in FIG. 2, the two rotors 3, 5 have two gears 17, 19 that mesh with one another, thus forming a synchronization unit (synchronizing transmission) that conveys the rotation of the upper rotor 3 to the lower rotor 5, which is the secondary rotor, at the desired RPM ratio; this ensures that the profile sections 7, 9 of the rotors 3, 5 mesh with one another without touching.

Rotor housing 1 is surrounding by a cooling jacket or cooling housing 21, which is for the most part designed as one-piece together with rotor housing 1, surrounding the same at a distance. Above and below, the cooling housing 21 has large openings that are closed off using a cover plate 23 and a base plate 25 fastened with bolts. Between the rotor housing 1 and the cooling housing 21, 23, 25 is an annular cooling space 27 surrounding the rotor housing 1 in which a liquid coolant circulates, such as water.

The screw compressor of the third stage shown in FIG. 2 is a “dry-rotor” similar to the screw compressors 60, 70 of the first and second stage; in other words its compression chamber is kept free of oil. Oil from the oil sump 76, which is circulated using an oil pump (not shown), is only used to lubricate the drive gear (gears 65, 75, 85, 95) and bearings 13, 15 as well as the synchronizing transmission (17, 19) of each screw compressor 60, 70, 80 (see 17, 19 in FIG. 2); however, the oil does not enter the compression chamber of the screw compressors.

At the left end of rotor housing 1 in FIG. 2 is a flange plate 84 that is removably attached using bolts, said plate serving to fasten the screw compressor to the mounting wall 91 of the gearbox. For this purpose, the flange plate 84 contains holes for attachment bolts. By replacing the flange plate 84 with a plate with another hole pattern, the position at which the screw compressor is fastened to the gearbox 90 can be changed.

In operating the compressor system shown in FIG. 1, air drawn in at inlet 61 of the first compressor stage 60 is compressed by it to a pressure in the range of 3 to 6 bar, preferably about 3.5 bar, and is then compressed to an intermediate pressure in the range of 10 to 15 bar, preferably about 12 bar, by the second compressor stage 70. This pre-compressed air goes from outlet 73 of the second stage 70 through a connecting line (not shown) to inlet 81 of the third compressor stage 80, where it is compressed to a final pressure in the range of 30 to 50 bar, preferably about 40 bar.

At the preferred operating pressures cited above, the pressure ratios in each of the three screw compressors 60, 70, 80 are nearly the same and decrease only minimally from the first to the third stage. At the pressures cited, the pressure ratio between the inlet ant outlet pressures in the first screw compressor 60 is approximately 3.5, in the second screw compressor 70 it is approximately 3.4 and in the third screw compressor 80 it is approximately 3.3.

FIG. 3 shows a perspective view, in part sectional, of the gearbox 90 with the transmission contained therein to drive the three screw compressors 60, 70, 80. The gearbox 90 has a perpendicular mounting wall 91 on one side, to which the housings of the three screw compressors 60, 70, 80 (not shown in FIG. 3) are attached. On the other side, the gearbox 90 is closed off by a bearing cover 92 inside of which is a drive shaft 94 held by means of a bearing ring 93 and supporting a drive gear 95. The end of the drive shaft 94 that extends beyond the drive gear 95 is held in a bearing seat (see FIG. 5) that is set into the mounting wall 91. The drive gear 95 meshes with the three driven gears 65, 75, 85 associated with the three screw compressors 60, 70, 80, said driven gears being distributed about the perimeter of the drive gear 95. Each of the driven gears 65, 75, 85 sits on a rotor shaft pin of one of the three screw compressors 60, 70, 80, said pin protruding into the gearbox 90 through a corresponding hole in the mounting wall 91.

In FIG. 4, the arrangement of the three drive gears 65, 75, 85 is shown in relation to the drive gear 95. The driven gears 65, 75 of screw compressors 60 or 70 of the first and second stage are located above the horizontal plane B-B that runs through the rotating axis A of the drive gear 95. On the other hand, the driven gear 85 of screw compressor 80 of the third stage is clearly below the horizontal plane B-B running through axis A, preferably near the lowest point T of the drive gear 95. It is preferable to locate the drive gear 65 for the first compressor stage such that a line C connecting its axis 65′ to axis A of the drive gear 95 assumes an angle α of not more than 30° with respect to the horizontal line B-B running through axis A of the drive gear 95. For driven gear 75 of the second compressor stage 70, the corresponding angle β is preferred not to be more than 20°. On the other hand, driven gear 85 of the third compressor stage 80 is located close enough to the lowest point T of the drive shaft 95 such that a line D connecting the axis of the driven gear 85 with the rotating axis A of the drive gear 95 assumes an angle γ of not more than 20° with respect to the vertical plane running through the axis A of the drive gear 95.

FIG. 5 shows a view of the mounting wall 91 of the gearbox 90. This view is shown with a cutout in the upper area in order to show the drive gear 95 located behind the wall, said gear engaging with the driven gears 65, 75, 85 of the three screw compressors 60, 70, 80 (left out in FIG. 5). The mounting wall 91 has openings 68, 78, 88 through which the shaft pins (see 7b in FIG. 2) of the screw compressors 60, 70, 80 that support the gears 65, 75, 85 can pass into the gearbox 90. The mounting wall 91 has rib-like raised mating flanges 69, 79, 89 that surround openings 68, 78, 88. Flanges 64, 74, 84 of the compressors 60, 70, 80 (see FIG. 1) are fastened to these mating flanges with bolts and suitable gaskets.

A bearing seat 97 is set into the mounting wall 91 of the gearbox 90. The end of the drive shaft 94 (see FIG. 3) supporting the drive gear 95 is held in this bearing seat. Both the bearing seat 97 and the bearing ring 93 shown in FIG. 3 to hold the drive shaft 94 are eccentrically designed. By exchanging the bearing ring 93 and the bearing seat 97 with others having varying eccentricities, the position of the drive gear 95 can be changed in the horizontal direction, as indicated with the horizontal double arrow 98 in FIG. 5.

Furthermore, the flange plate 84 of screw compressor 80 that constitutes the third stage is removably bolted to the mating flange 89 of the gearbox, along with the rotor housing associated with it. This flange plate can be exchanged with a flange plate having a different hole pattern, which allows the position of the screw compressor 80 and thus its driven gear 85 to change in the vertical direction as indicated by the vertical double arrow 86 in FIG. 5.

This ability to shift the drive gear 95 in the horizontal direction 98 and to shift the driven gear of the third stage in the vertical direction 86 enables the use of different gear sets for gears 95, 65, 7585 that make up the transmission, whereupon the gear ratios and thus the relative RPM's of the three compressor stages 60, 70, 80 can be changed by using different diameters matched with one another. In the process, all four gears 65, 75, 85, 95 that make up the transmission can be exchanged with such other diameters, wherein a shift of only two of these elements in two directions perpendicular to one another is sufficient, namely the drive gear 95 in the horizontal direction 98 and the gear 85 of the third stage in the vertical direction 86, to ensure proper meshing of the gears even when the diameter ratios are changed.

Claims

1. A multi-staged screw compressor system comprising: a gearbox;a drive gear located in the gearbox;the multi stage screw compressor system consisting of a first screw compressor; a second screw compressor; and a third screw compressor;the first screw compressor, the second screw compressor, and the third screw compressor fastened to the gearbox and coupled to the drive gear such that the first screw compressor, the second screw compressor, and the third screw compressor are all driven in common by the drive gear and are spaced circumferentially around the drive gear such that the first screw compressor, the second screw compressor, and the third screw compressor are positioned in a nonlinear orientation relative to one another as defined by a plane extending radially through an axis of rotation of the drive gear, wherein during operation the first screw compressor compresses a flow of gaseous fluid from an inlet pressure to a first intermediate pressure, the second screw compressor compresses the flow of fluid from the first intermediate pressure to a second intermediate pressure, and the third screw compressor compresses the flow of fluid from the second intermediate pressure to a final pressure, wherein the final pressure is at least thirty times the inlet pressure.

2. The screw compressor system according to claim 1, wherein the inlet pressure is approximately 1 bar, the first intermediate pressure is 2 to 6 bar, the second intermediate pressure is 10 to 15 bar, and the final pressure is 30 to 50 bar.

3. The screw compressor system according to claim 1, wherein the first screw compressor, the second screw compressor, and the third screw compressor are each dry running screw compressors.

4. The compressor system according to claim 1, wherein the first screw compressor, the second screw compressor, and the third screw compressor each include two screw rotors, one of which includes a shaft pin that supports respective driven gears that each mesh with the drive gear, wherein the drive gear and driven gears include respective rotating axes, and wherein a plane passing through the rotating axis of the drive gear and the driven gear of the first screw compressor assumes an angle (α) of not more than 30 degrees with respect to the horizontal plane running through the rotating axis of the drive gear.

5. The compressor system according to claim 1, wherein the first screw compressor, the second screw compressor, and the third screw compressor each include two screw rotors, one of which includes a shaft pin that supports respective driven gears that each mesh with the drive gear, wherein the drive gear and driven gears include respective rotating axes, and wherein a plane passing through the rotating axis of the drive gear and the driven gear of the second screw compressor assumes an angle (β) of not more than 20 degrees with respect to the horizontal plane running through the rotating axis of the drive gear.

6. The compressor system according to claim 1, wherein the first screw compressor, the second screw compressor, and the third screw compressor each include two screw rotors, one of which includes a shaft pin that supports respective driven gears that each mesh with the drive gear, wherein the drive gear and driven gears include respective rotating axes, and wherein a plane passing through the rotating axis of the drive gear and the driven gear of the third screw compressor assumes an angle (γ) of less than 20 degrees with respect to the vertical plane running through the rotating axis of the drive gear.

7. The compressor system according to claim 1, wherein the gearbox has a perpendicular mounting wall, a drive shaft rotatably held on a horizontal axis in the gearbox and supporting the drive gear, and wherein the drive shaft supporting the drive gear is held by exchangeable bearing parts that have differing eccentricities in the horizontal direction, such that by changing the exchangeable bearing parts, the position of the rotating axis of the drive shaft in the gearbox can be shifted in the horizontal direction.

8. The compressor system according to claim 7, wherein the first screw compressor, the second screw compressor, and the third screw compressor each include two screw rotors, one of which includes a shaft pin that supports respective driven gears that each mesh with the drive gear, and wherein to change the RPM ratio of the first screw compressor, the second screw compressor, and the third screw compressor of the compressor system, exchangeable gear sets are made available, each of which consists of an additional drive gear and additional driven gears of varying diameters together with additional associated bearing parts and flange parts with which to adjust the position of the drive gear in the horizontal direction and the driven gear of the third screw compressor in the vertical direction.

9. The compressor system according to claim 1, wherein the gearbox has a perpendicular mounting wall, and wherein the third screw compressor is attached to the mounting wall by exchangeable flange parts such that by changing the exchangeable flange parts the position of the third screw compressor can be changed in the vertical direction relative to the gearbox.

10. The compressor system according to claim 1, wherein the first screw compressor has an outlet pressure of 2 to 6 bar, the second screw compressor has an outlet pressure of 10 to 15 bar, and the third screw compressor has an outlet pressure of 30 to 50 bar.

11. A multi-staged screw compressor system comprising: a gearbox including a housing having a mounting wall;a drive gear supported by the housing for rotation about a drive axis, the drive axis dividing the drive gear into a first upper quadrant, a second upper quadrant, a first lower quadrant, and a second lower quadrant, each quadrant extending between a vertical plane and a horizontal plane that intersect on the drive axis;a first mating flange, a second mating flange, and a third mating flange each formed as part of the mounting wall to define three substantially planar surfaces arranged normal to the drive axis;a low pressure screw compressor coupled to the first mating flange and including a first driven gear, the first driven gear disposed completely within the first upper quadrant;a middle pressure screw compressor coupled to the second mating flange and including a second driven gear, the second driven gear disposed completely within the second upper quadrant;a high pressure screw compressor coupled to the third mating flange and including a third driven gear, the third driven gear disposed within at least one of the first lower quadrant and the second lower quadrant, wherein the low pressure screw compressor, the middle pressure screw compressor, and the high pressure screw compressor cooperate to compress a gas from a first pressure to a second pressure that is at least 30 times the first pressure; andmeans for changing eccentricity between the drive gear and the first, second and third driven gears.

12. The multi-staged screw compressor system of claim 11, wherein the low pressure screw compressor includes a first rotor and a second rotor that meshes with the first rotor.

13. The multi-staged screw compressor system of claim 12, further comprising a synchronization unit that couples the first rotor and the second rotor for rotation.

14. The multi-staged screw compressor system of claim 11, wherein the low pressure screw compressor is positioned such that a line extending between the drive axis and a rotational axis of the first driven gear defines an angle of not more than 30 degrees with respect to the horizontal plane.

15. The multi-staged screw compressor system of claim 11, wherein the middle pressure screw compressor is positioned such that a line extending between the drive axis and a rotational axis of the second driven gear defines an angle of not more than 20 degrees with respect to the horizontal plane.

16. The multi-staged screw compressor system of claim 11, wherein the high pressure screw compressor is positioned such that a line extending between the drive axis and a rotational axis of the third driven gear defines an angle of not more than 20 degrees with respect to the vertical plane.

17. The multi-staged screw compressor system of claim 11, wherein a portion of the third driven gear is positioned in the first lower quadrant and a portion of the third driven gear is positioned in the second lower quadrant.

18. The multi-staged screw compressor system of claim 11, wherein the low pressure screw compressor has an outlet pressure of about 2 to 6 bar, the middle pressure screw compressor has an outlet pressure of about 10 to 15 bar, and the high pressure screw compressor has an outlet pressure of about 30 to 50 bar.

19. The multi-staged screw compressor system of claim 11, wherein the means for changing eccentricity includes a plurality of exchangeable bearing parts, each exchangable bearing part having a different eccentricity configured to position the drive axis in a desired position between first and second positions along the horizontal plane and to position the third driven gear in a desired position between first and second positions in the vertical plane.

20. The multi-staged screw compressor system of claim 11, wherein the low pressure screw compressor includes one of a plurality of selectable flange plates, each of the plurality of flange plates including a different hole pattern such that the selection of the one of the plurality of flange plates determines the position of the low pressure screw compressor with respect to the horizontal plane.

21. A method to change the output of a multi-stage compressor system comprising: providing a housing to support a plurality of gear eccentricity configurations for the multistage compressor system, wherein gear eccentricity is defined as a distance between a rotational axis of two or more coupled gears;positioning a drive gear in a first location with respect to the housing, the drive gear being selectively positioned in one of a plurality of discreet locations between first and second bounding positions in a linear direction;rotatable connecting first, second and third driven gears to the housing such that each driven gear is in operable engagement with the drive gear to define a first gear eccentricity configuration, wherein the third driven gear is selectively positioned in one of a plurality of discreet locations along a direction perpendicular to the linear direction of the drive gear;connecting first, second and third compressors to the first, second and third driven gears, respectively to provide a first compressor system output; andreconfiguring the multistage compressor to provide a second compressor system output.

22. The method of claim 21, wherein the reconfiguring comprises: removing the first, second and third compressors;moving the drive gear to a second location between the first and second bounding positions;moving the third gear to a different location in response to the moving of the drive gear;changing at least one of the first and second driven gears in response to the moving of the drive gear; andengaging the first, second and third driven gears with the drive gear to define a second gear eccentricity configuration.

23. The method of claim 22 further comprising: reconnecting the first, second and third compressors to the first, second and third driven gears, respectively to provide the second compressor system output.

24. The method of claim 22, wherein the moving of the drive gear and the third gear includes: selecting one of a plurality of differently sized bearing assemblies to position the drive gear and the third driven gear in a desired location relative to the housing.

25. A method to change the output of a multi-stage compressor system comprising: providing a housing configured to support changing the multi-stage compressor system from a first gear eccentricity to a second gear eccentricity;wherein the first gear eccentricity comprises: selectively positioning a drive gear in a first position with respect to the housing, wherein the first position is selected from one of a plurality of locations defined along a linear path,engaging first, second and third driven gears with the drive gear;connecting first, second and third compressors to the first, second and third driven gears, respectively to provide a first output of the multistage compressor; andwherein changing to the second gear eccentricity comprises: selecting one of a plurality of differently sized bearing assemblies to position the drive gear in a second location along the linear path;changing the size of the first and second driven gears to engage with the drive gear in the second location;moving the third gear along a path perpendicular to the linear path of the drive gear to engage with the drive gear in the second location; andwherein the second gear eccentricity provides a second output of the multistage compressor.