SCREW SPINDLE PUMP

Abstract

A screw spindle pump, comprising a pump housing having a lead screw received therein and at least one running spindle which meshes with said lead screw, as well as a connector housing which is placed onto the pump housing and has a suction connector and a pressure connector, the two latter fluidically communicating with a suction inlet and a pressure outlet of the pump housing, wherein the connector housing is composed of a first housing part and a second housing part, one of the two latter having the suction connector and the other having the pressure connector, both said housing parts being rotatable relative to the pump housing and both being rotatable relative to one another.

Claims

1. A screw spindle pump, comprising a pump housing having a lead screw received therein and at least one running spindle which meshes with said lead screw, as well as a connector housing which is placed onto the pump housing and has a suction connector and a pressure connector, the two latter fluidically communicating with a suction inlet and a pressure outlet of the pump housing, wherein the connector housing is composed of a first housing part and a second housing part, one of the two latter having the suction connector and the other having the pressure connector, both said housing parts being rotatable relative to the pump housing and both being rotatable relative to one another.

2. A screw spindle pump according to claim 1, wherein each housing part is rotatable relative to the pump housing by at least 45°.

3. A screw spindle pump according to claim 2, wherein each housing part is rotatable relative to the pump housing by 360°.

4. A screw spindle pump according to claim 1, wherein sealing elements by way of which the housing parts are mutually sealed and at least one housing part is also sealed in relation to the pump housing.

5. A screw spindle pump according to claim 4, wherein the housing part that has the suction connector is sealed in relation to the housing part that has the pressure connector, and the housing part that has the pressure connector is sealed in relation to the pump housing.

6. A screw spindle pump according to claim 4, wherein one of the housing parts has a cylindrical flange which extends axially and engages in an annular beading on the other housing part, wherein the sealing element that mutually seals the two housing parts seals between the flange and the annular beading.

7. A screw spindle pump according to claim 4, wherein annular seals that are inserted in annular receptacles are provided as sealing elements.

8. A screw spindle pump according to claim 1, wherein the suction inlet is formed by one radial inlet opening, or a plurality of radial inlet openings configured so as to be distributed in the circumferential direction on the pump housing, which opens out into a suction chamber that is configured between the one housing part and the pump housing, and the pressure outlet is formed by one radial outlet opening, or a plurality of radial outlet openings configured so as to be distributed in the circumferential direction on the pump housing, which opens out into a pressure chamber that is configured between the second housing part and the pump housing.

9. A screw spindle pump according to claim 8, wherein at least two inlet openings and at least four outlet openings are provided.

10. A screw spindle pump according to claim 8, wherein further axial inlet openings that form the suction inlet are configured on an end-proximal base of the pump housing.

11. A screw spindle pump according to claim 1, wherein only one radial suction connector, or one radial suction connector and one axial suction connector, is/are provided on the suction-proximal housing part.

12. A screw spindle pump according to claim 11, wherein in the instance of two suction connectors one thereof is closed by means of a releasable closure element, in particular a closure plug.

13. A screw spindle pump according to claim 1, wherein the housing parts in distinguished or arbitrary rotated positions relative to one another are fixable on one another, and one housing part in terms of the rotated position thereof in distinguished or arbitrary positions relative to the pump housing is fixable on the latter.

14. A screw spindle pump according to claim 13, wherein screw connections are provided for fixing.

15. A screw spindle pump according to claim 14, wherein a plurality of axial through bores are provided so as to be distributed in the circumferential direction on the end-proximal housing part, and a plurality of axial internal-thread bores are provided so as to be distributed at the same pitch in the circumferential direction on the neighboring housing part, and/or in that a plurality of axial through bores are provided so as to be distributed in the circumferential direction on a radial flange of the pump housing, and a plurality of axial internal-thread bores are provided so as to be distributed at the same pitch in the circumferential direction on the neighboring housing part.

16. A screw spindle pump according to claim 15, wherein the through bores and internal-thread bores have a pitch between 15° and 90°, in particular between 22.5° and 45°.

17. A screw spindle pump according to claim 1, wherein at least two axially open slots are provided so as to extend in the circumferential direction on the end-proximal housing part, and a plurality of axial internal-thread bores are provided so as to be distributed in the circumferential direction on the neighboring housing part, and/or or in that at least two axial slots are provided so as to extend in the circumferential direction on a radial flange of the pump housing, and a plurality of axial internal-thread bores are provided so as to be distributed in the circumferential direction on the neighboring housing part.

18. A screw spindle pump according to claim 1, wherein a plurality of discharge bores which are provided with releasable closure plugs and lead into the interior of the connector housing are provided so as to be distributed in the circumferential direction on each housing part.

19. A screw spindle pump according to claim 18, wherein three discharge bores which are disposed so as to be mutually offset by 90° are provided per housing part.

20. A screw spindle pump according to claim 1, wherein a flat fastening region having a plurality of internal-thread bores for fastening a line to be connected to the suction connector and to the pressure connector is configured in the region of the suction connector and pressure connector on both housing parts.

21. A screw spindle pump according to claim 20, wherein an adapter plate which is able to be releasable fastened to the fastening region and which has fastening installations, in particular internal-thread bores, for fastening at least one connector flange plate is provided.

22. A screw spindle pump according to claim 1, wherein a stand element which is preferably able to be releasably attached to the pump housing is provided.

23. A screw spindle pump according to claim 22, wherein the stand element is L-shaped or U-shaped and has a leg having at least two bores provided thereon, screw connections by way of which the pump housing is connected to the neighboring housing part engaging through said bores.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0030] In the drawing:

[0031] FIG. 1 shows an exploded view of a screw spindle pump according to the invention;

[0032] FIG. 2 shows a sectional view through a screw spindle pump according to the invention;

[0033] FIG. 3 shows a plan view in the direction of the arrow III from FIG. 2;

[0034] FIG. 4 shows a view of the end side in the direction of the line IV in FIG. 2;

[0035] FIGS. 5-16 show various perspective views of dissimilar types of screw spindle pumps which are able to be produced from the elements shown in FIG. 1, having in each case the same positioning of the pump housing but a variable disposal of the first and the second housing part as well as of the suction connector;

[0036] FIG. 17 shows an exploded view of a screw spindle pump according to the invention in a further embodiment; and

[0037] FIG. 18 shows the assembled screw spindle pump from FIG. 17.

DETAILED DESCRIPTION OF THE INVENTION

[0038] FIG. 1 shows an exploded illustration of a screw spindle pump 1 according to the invention. Said screw spindle pump 1 comprises a pump housing 2 in which a lead screw 3 (cf. FIG. 2), which by way of a connection pin 4 is to be connected to a drive motor (not shown in more detail) that is to be connected to the pump housing 2, as well as at least one running spindle 16 which meshes with the lead screw 3 are received. The pump housing 2 has a cylindrical housing portion 5 which is axially delimited by way of a base plate 6 of an end-proximal base part 7. This base part 7 by way of corresponding screw connections 8 is connected to a second pump housing part 9 which, besides the further part of the cylindrical portion 5, has a radial flange 10 and which is furthermore axially delimited by way of an end-proximal flange 11 to which the housing of the drive motor is to be fastened. To this end, corresponding fastening bores 12 for placing corresponding connection screws are provided.

[0039] Trough-shaped depressions 13 which serve for placing connection screws 14, with the aid of which a connector housing (yet to be described hereunder) is fixed to the pump housing 2 are configured in the region between the radial flange 10 and the connector flange 11.

[0040] First inlet openings 15 are provided on the cylindrical portion 5 of the pump housing 2 in the region of the base plate 6, wherein two such inlet openings 15 are provided so as to be mutually opposite. The inlet openings 15 are of a quasi-rectangular cross section and configured in the manner of windows and extend over an angular segment of approx. 90°, for example. The running spindle 16 can be seen through the inlet opening 15 shown in FIG. 1. These inlet openings 15 define a suction inlet 17 which is furthermore formed by axial inlet openings 18 which are configured on the base plate 6. Fluid to be conveyed makes its way into the operating region of the spindles 3, 16 by way of this suction inlet 17.

[0041] Furthermore configured on the pump housing 2 are a plurality of outlet openings 20 in the form of radial bores forming a pressure outlet 19, wherein four inlet openings 20 which are mutually offset by 90° are provided in the example shown. The conveyed fluid exits said inlet openings 20 again at a corresponding pressure.

[0042] Furthermore provided are two annular receptacles 21 which are provided on the cylindrical portion 5 and in which in each case one annular seal 22 which serves for sealing in relation to the connector housing is inserted, cf. FIG. 2. Simple O-rings are thus used as annular seals.

[0043] In the case of the assembled pump, a connector housing 23 is pushed onto the pump housing 2, or the pump housing 2 by way of the cylindrical portion 5 thereof is pushed into the connector housing 23, respectively. The connector housing 23 is composed of a first housing part 24 which is embodied in the manner of a pot and has a base 25 as well as a cylindrical cavity 26 in which the front end of the pump housing 2 engages, cf. FIG. 2. The first housing part 24 has a first suction connector 27 in the form of a radial internal-thread bore which is configured on a flat fastening portion 28 which offers a flat fastening interface for an infeed line to be connected or for an adapter plate yet to be described hereunder. Four internal-thread bores 29 to which either the line or the adapter plate can be screwed are configured on the fastening portion 28.

[0044] Furthermore shown is a closure plug 30 having an assigned annular seal 31, said closure plug 30 to be optionally placed. The closure plug 30 is screwed into the suction connector 27 if the latter is not to be required.

[0045] This is the case when the second suction connector 32, which is configured on the base plate 25 and is likewise configured in the form of an internal-thread bore and is likewise assigned four fastening bores 33 for connecting the infeed line, or an adapter plate, is used. Since such an optional axial connection of an adapter plate is presently illustrated, cf. FIG. 1, the closure plug 30 would consequently have to be screwed into the first pressure connector 27. Should the adapter plate be placed on the first pressure connector 27, the closure plug 30 would of course have to be screwed into the second pressure connector 32.

[0046] The first housing part 24 on the base plate 25 furthermore has a plurality of through bores 34 through which corresponding connection screws 35 which effect corresponding screw connections and which serve for fixedly connecting the first housing part 24 to a second, axially adjoining, housing part which is to be described hereunder, are driven in.

[0047] Furthermore provided on the first housing part 24 are a total of three discharge bores 36 which are preferably disposed so as to be offset by 90°, one of said discharge bores 36 being shown in FIG. 1 and one in FIG. 2, and which are in each case closed by means of a closure plug 37 having an assigned annular seal 38. Fluid situated in the pump can be discharged by way of these discharge screws in the case of maintenance.

[0048] Furthermore shown is a second housing part 39 which is axially contiguous to the first housing part 24 and, when pushed onto the cylindrical shoulder 5 of the pump housing 2, is disposed between the first connector housing 24 and the radial flange 10. Said second housing part 39 is embodied as a hollow cylinder, thus having a hollow-cylindrical internal shape, cf. FIG. 2, wherein two annular shoulders 40 which project radially inward are configured on the internal circumference, cf. FIG. 2, the respective annular seal 22 bearing in a sealing manner on said annular shoulders 40. In this way, two mutually separate chambers are configured when viewed in the axial direction of the pump, specifically a suction chamber 41 in the region of the first housing part 24 and of the second housing part 39 up to the first annular shoulder 40 and the sealing plane situated there, wherein the two suction connectors 27, 32 open into the suction chamber 41, as well as a pressure chamber 42 between the second housing part 39 and the pump housing 2 in the region between the two sealing planes formed by way of the annular seals 22, wherein the pressure connector 43 which is configured on the second housing part 39 opens out into this suction chamber, cf. FIG. 2. The outlet openings 20 also open out into this pressure chamber 42, just like the two inlet opening 15 open into the suction chamber 41, such that there is a fluidic connection from the respective suction connector 27, 32 to the pressure connector 43.

[0049] The pressure connector 43 here too is configured on a flat fastening portion 44 and is again embodied in the form of an internal-thread bore. The flat fastening portion 44 again serves as a fastening interface for a discharging line or for an adapter plate yet to be described hereunder. Corresponding internal-thread bores 45 are also provided here for fastening the line, or the adapter plate, respectively.

[0050] The second housing part 39 also has three discharge bores 46 which are disposed so as to be distributed by 90°, for example, and which are closed by way of corresponding closure plugs 47 having an assigned annular seal 48. Fluid situated in the pressure chamber 42 can be discharged by way of said discharge bores 46, while fluid situated in the suction chamber can be discharged by way of the discharge bores 36.

[0051] In order for the two housing parts 24, 39 in the push-fitted state to be fastened to one another by way of the connection screws 35, axially running internal-thread bores 49, just like the through bores 34, are provided on the end side of the second housing part 39. The connection screws 35 are screwed into said internal-thread bores 49 such that the two housing parts 24, 39 are fixedly screwed to one another in an axial manner. In order for said two housing parts 24, 39 to also be mutually sealed, the first housing part 24 has an axially extending annular flange 50, cf. FIG. 2, which engages in an annular beading 51 on the second housing part 39. An annular seal 53 in the form of an O-ring is received in an annular receptacle 52 on the annular flange 50 such that the two housing parts 24, 39 are mutually sealed in a radial manner.

[0052] As is shown in FIG. 1, the through bores 34 and the internal-thread bores 49 are offset so as to be equidistant about the circumference. Said through bores 34 in the example shown have a pitch, or a pitch angle, respectively, of 45°. This means that the two housing parts 24, 39 can be disposed and mutually fixed at different rotated positions relative to one another.

[0053] In the context of assembling, the second housing part 39 is first pushed onto the cylindrical portion 5 on which the corresponding annular seals 22 are already disposed, until said second housing part 39 bears on the radial flange 10. Thereafter the second housing part 24 on which the annular seal 53 is disposed is pushed on. The two housing parts 24, 39 are brought to the desired rotated position relative to one another just like said two housing parts 24, 39 are also conjointly brought to a desired rotated position relative to the pump housing 2, or to the radial flange 10, respectively. Once the corresponding rotated positions are assumed, the two housing parts 24, 39 by way of the connection screws 35 are fixedly screwed to one another, on the one hand, and the entire connector housing 23 is fixed by way of the connection screws 14 which are driven through corresponding through bores 54 on the radial flange 10 and screwed into corresponding axial internal-thread bores 55 on the end side of the second housing part 39, on the other hand. All three housing parts are thus brought to a desired rotated position relative to one another, on the one hand, but are also fixedly screwed to one another in an axial manner, on the other hand.

[0054] As described, there is either the possibility for the respective line at the required suction connector 27 or 32 as well as at the pressure connector 43 to be screwed directly to the fastening portion 28, or the base 25, or the fastening portion 44, respectively, corresponding connection screws 56, 57 serving to this end. The corresponding line is sealed in relation to the corresponding fastening portion 28, 44 or to the base 25 by a corresponding annular seal 58, 59. The direct fastening in this case takes place at a standard fastening interface.

[0055] In principle however, it is also possible for an adapter plate 60, 61 to be screwed onto the respective fastening portion 28, 44 or the base 25 by means of the connection screws 56, 57, while disposing therebetween the annular seals 58, 59. The adapter plates 60, 61 have corresponding through bores 62, 63 which are then penetrated by the corresponding connection screws 56, 57 which are screwed into the internal-thread bores 29 or 33 or 45, respectively. The adapter plates 60, 61 in the example shown furthermore have four further internal-thread bores 64, 65 which serve for fastening a connector flange plate 66, 67, the latter to this end having corresponding through bores 68, 69 through which the corresponding connection screws 70, 71 are driven and screwed into the internal-thread bores 64, 65 of the adapter plates 60, 61. Instead of the internal-thread bores 64, 65, it would also be conceivable for through bores to be provided and for the connection screws 70, 71 to be screwed into the internal-thread bore 29, 30, or 45, respectively. Here too, one annular seal 72, 73 is disposed therebetween, said annular seal 72, 73 being configured in a corresponding annular receptacle 74, 75 on the adapter plate 60, 61. This connector flange plate 66, 67 furthermore has internal-thread bores 76, 77 into which connection screws (not shown in more detail) are screwed, the corresponding line then being fastened by means of said connection screws. The disposal of these internal-thread bores 76, 77 can differ from one connector flange plate to another connector flange plate, this means that dissimilar connector flange plates having dissimilar bore patterns and thus connection geometries of different standards can be attached.

[0056] Furthermore provided is a stand element 78 which here is embodied so as to be L-shaped and has a vertically running fastening leg 79 on which corresponding through bores 80 which are penetrated by two fastening screws 14 which serve for connecting the radial flange 10 to the second housing part 39 are configured such that the stand element 78 herewith can be selectively fastened to the pump. The stand element 78 by way of a second horizontally running leg 81 bears on the floor[possibly->‘base’?] such that the screw spindle pump 1 is supported by way of said leg 81.

[0057] FIG. 2, as described, shows a sectional view through a screw spindle pump 1 according to the invention, wherein the adapter plate 60, deviating from the illustration in FIG. 1, here is disposed on the suction connector 27, while the suction connector 32 is closed by way of the closure plug 30. As can be seen, the suction connector 27 which in a radially outward manner by way of the corresponding bores in the adapter plate 60 and the connector flange plate 66 is of course extended in length, opens out into the suction chamber 41 which extends up to the first sealing plane, the latter being implemented by way of the first sealing element which in an axial manner follows toward the right and is in the form of the annular seal 22. Inflowing fluid, or suction fluid, respectively, by way of the inlet openings 15 makes its way into the pump housing 2 and therein is guided by the spindles 3, 16 to the outlet openings 20 where said fluid exits into the surrounding annular suction chamber 42 and makes its way to the pressure connector 43, the latter here of course also being extended in length in an outward manner by way of corresponding bores in the adapter plate 61 and the connector flange plate 67.

[0058] As already described, there is the possibility for bringing the two housing parts 24 and 39 to a variable relative position in relation to one another, on the one hand, as well is for bringing the two housing parts 24, 39 to a variable relative position in relation to the pump housing 2. This means that there is double rotatability. This is possible since the pump housing 2 has the cylindrical portion 5, while the two housing parts 24, 39 have corresponding internal cylindrical geometries such that a rotation is possible. At the same time, the housing parts are mutually sealed by way of the corresponding annular seals, wherein these annular seals permit rotation and nevertheless correspondingly seal in the desired rotated position. Particular requirements as a result of the rotatability are not to be set for the annular seals since the housing parts are rotated in a mutually relative manner only once in the context of assembling; the housing parts, or the connector housing, respectively, is/are subsequently fixedly screwed to the pump housing.

[0059] FIG. 2 shows an arrangement in which the two housing parts 24, 39 are disposed so as to be mutually aligned in an axial manner in terms of the pump longitudinal axis, cf. to this end also FIGS. 3 and 4. By virtue of the rotatability of the two housing parts 24, 39 relative to one another as well as relative to the pump housing 2, there is however a multiplicity of further potential arrangements or potential alignments, respectively. The latter are ultimately limited, or limited to defined connecting positions, respectively, only by the pitch of the respective through bores 34 and internal-thread bores 49 on the two connector housings 24, 39, or 54, 55, respectively, on the radial flange 10 and the second connector housing 39. It is assumed that the pitch in both connection planes corresponds in each case to 45°.

[0060] FIGS. 5 to 16 show a total of twelve exemplary arrangements of how the suction connectors 27 or 32, respectively, and the pressure connector 43 can be positioned relative to one another. The position of the pump housing 2 is in each case identical in all variants shown in FIGS. 5 to 16, only the housing parts 24 and 39 are brought to dissimilar positions either only relative to the pump housing 2 or else relative to one another.

[0061] FIGS. 5, 6, and 7 show a linear disposal of the suction and pressure connectors 27, 43, thus along the pump longitudinal axis. While said suction and pressure connectors 27, 43, proceeding from FIG. 5 and when viewed on to the fastening flange 11 of the pump housing 2, are directed toward the right in FIG. 5, said suction and pressure connectors 27, 43 in FIG. 6 stand in a vertically upward manner, so to speak, while said suction and pressure connectors 27, 43 are directed toward the left in FIG. 7. The housing parts 24, 39 here are thus not rotated relative to one another but are in different positions which differ by 90°.

[0062] The suction connector 27 in FIG. 8 is directed toward the right, while the pressure connector 43 is directed upward. Both have a mutual angle of 90°, are thus fastened to one another by means of the connection screws 35 so as to be mutually rotated by two pitches of 45°.

[0063] The pressure connector 43 in the design embodiment according to FIG. 9 is disposed so as to be rotated further by yet again 90° such that the suction connector 27 and the pressure connector 43 are directed in opposite directions, the two housing parts 24, 39 thus consequently being mutually rotated by 180°.

[0064] In the design embodiment according to FIG. 10 the suction connector, proceeding from FIG. 9, is rotated by 90° and points vertically upward, while the pressure connector 43 like before is directed toward the left. A 90° configuration is again provided here.

[0065] The suction connector 27 in the design embodiment according to FIG. 11 again points upward, while the pressure connector 43 is directed toward the right.

[0066] In the design embodiment according to FIG. 12 the suction connector 27 is rotated relative to the pressure connector 43 by a further 90°. Both point in opposite directions, the housing parts 24, 39 thus being mutually rotated by 180°. This variant is the mirror-image design embodiment of the arrangement according to FIG. 9.

[0067] FIG. 13 finally shows an arrangement in which the suction connector 27 is directed toward the left, while the pressure connector 43 is again directed upward; both are at a mutual angle of 90°.

[0068] All of the configurations are able to be readily set by virtue of the 45° pitch provided in terms of the through bores and internal-thread bores. In principle, further arrangements can also be implemented as a result of the 45° pitch. That is to say that the suction connectors 27 and the pressure connectors 43 can also be mutually disposed at an angle of 45° or at 35°, if required.

[0069] FIGS. 14, 15, and 16 show three variants of arrangement in which the axial suction connector 32 is utilized. While the axial suction connector 32 by way of the closure plug 30 is closed in the design embodiments according to FIGS. 5 to 13, the radial suction connector 27 is closed by way of the closure plug 30 in the design embodiments according to FIGS. 14 to 16. Here, there is the possibility of varying the relative position of the radial pressure connector 43 relative to the axial suction connector 32. While said radial pressure connector 43 in FIG. 14 is directed toward the right, said radial pressure connector 43 according to the design embodiment according to FIG. 15 stands in a vertically upward manner. In the design embodiment according to FIG. 16 the pressure connector 43 is finally directed toward the left.

[0070] Here too, by virtue of the 45° pitch, there is the possibility of also bringing the pressure connector 43 to intermediate positions which differ by 45°.

[0071] All these different pump configurations can be implemented with one and the same set of pump components. This is because the modular system according to the invention enables these different configurations to be configured by simply rotating the components relative to one another while using a standardized pump housing 2 and using two standardized housing parts 24, 39. This offers an extremely high degree of flexibility in terms of the design embodiment of the pump and at the same time simplicity, since only the standardized pump housings 2 having the likewise standardized internal components thereof (spindles, etc.) as well as standardized first housing parts 24 and second housing parts 39 have to be stocked.

[0072] FIGS. 17 and 18 show a further embodiment of a screw spindle pump 1 according to the invention in the form of simplified schematic illustrations, wherein the same reference signs are used for the same components. For reasons of simplicity, only a reduced number of components is shown here in the exploded illustration according to FIG. 17. In principle however, the basic construction of this screw spindle pump also corresponds to that described above.

[0073] Provided here is also a pump housing 2 as well as a connector housing 23 comprising a first housing part 24 and a second housing part 39. Said housing parts 24 and 39 are in turn pushed onto the cylindrical portion of the pump housing 2 in the manner described above and by way of corresponding sealing elements are sealed relative to one another and in relation to the pump housing 2. In this design embodiment, a radial flange 82 is placed between the two housing parts 24, 39. Said radial flange 82 has through bores 83 which are in alignment with the through bores 34 on the first housing part 24. The connection screws 35 penetrate the through bores 34 and 83, and here too are screwed into the corresponding internal-thread bores 49 on the second housing part 39.

[0074] The radial flange 82 furthermore has through bores 84 which in a radial manner lie further outward and serve for receiving connection screws by way of which the screw spindle pump 1 can be screwed to a fastening geometry which is not shown in more detail.

[0075] In this design embodiment, a suction tube 85, which has a fastening flange 86 having through bores 87 through which the connection screws 56 which are screw-fitted in the internal-thread bores 33 of the base 25 of the first housing part 24 are guided, is connected to the axial suction inlet 32. This is of course performed while disposing therebetween the annular seal 58, this however not being shown in more detail here.

[0076] The second suction connector 27 here is closed by means of the closure plug 30.

[0077] An adapter plate 61 by means of the fastening screws 57 is fixed to the fastening portion 44 having the pressure connector 43, as has already been described above.

[0078] This design embodiment enables the configuration of an immersion pump which can be assembled in a tank, either in a horizontal or vertical arrangement.

[0079] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.