ROTARY PUMP FOR CONVEYING A FLUID

Abstract

A rotary pump for conveying a fluid, includes a pump housing, a pump shaft, a hydraulic unit, a mechanical seal, and a stator. The hydraulic unit conveys and pressurizes the fluid, includes an impeller fixedly mounted on the pump shaft, and during operation generates an axial thrust to act on the pump shaft. The mechanical seal seals the pump shaft and includes a rotor connected to the pump shaft in a torque proof manner. The stator is stationary with respect to the pump housing. The mechanical seal is arranged between the hydraulic unit and an end of the pump shaft, and is a balancing device configured to generate an axial force on the pump shaft during operation, with the axial force configured to counteract the axial thrust.

Claims

1. A rotary pump for conveying a fluid, comprising: a pump housing with an inlet to receive the fluid having a suction pressure and an outlet to discharge the fluid having a discharge pressure; a pump shaft configured to rotate about an axial direction; a hydraulic unit to convey and pressurize the fluid, the hydraulic unit comprising an impeller fixedly mounted on the pump shaft, and during operation the hydraulic unit is configured to generate an axial thrust to act on the pump shaft; and a mechanical seal to seal the pump shaft, the mechanical seal including a rotor connected to the pump shaft in a torque proof manner, and a stator configured to be stationary with respect to the pump housing, and the mechanical seal being arranged between the hydraulic unit and an end of the pump shaft, and the mechanical seal being a balancing device configured to generate an axial force on the pump shaft during operation, with the axial force configured to counteract the axial thrust.

2. The rotary pump in accordance with claim 1, wherein the mechanical seal has a sealing diameter configured to balance the axial thrust generated by the hydraulic unit.

3. The rotary pump in accordance with claim 1, wherein the rotor comprises a rotor seal ring having an inner diameter which is at least 15 mm larger than a diameter of the pump.

4. The rotary pump in accordance with claim 1, wherein the mechanical seal has a sealing diameter, which is at least 15 mm larger than a diameter of the pump shaft.

5. The rotary pump in accordance with claim 1, wherein the mechanical seal is configured to seal a pressure difference, which is at least as large as a difference between the discharge pressure and the suction pressure.

6. The rotary pump in accordance with claim 1, wherein the mechanical seal has a front side facing the hydraulic unit, and a back side facing away from the hydraulic unit, and the front side is arranged adjacent to the impeller of the hydraulic unit, such that the front side of the mechanical seal is exposed to essentially a same pressure as a back side of the impeller.

7. The rotary pump in accordance with claim 6, wherein the front side of the mechanical seal is arranged to be exposed to a pressure, which is essentially a same as the discharge pressure.

8. The rotary pump in accordance with claim 6, wherein the back side of the mechanical seal is arranged to be exposed to a pressure, which is essentially a same as the suction pressure or an ambient pressure prevailing at an outside of the pump housing.

9. The rotary pump in accordance with claim 1, further comprising a disaster bushing configured to restrict leakage of the fluid through the mechanical seal in an event of a failure of the mechanical seal.

10. The rotary pump in accordance with claim 1, wherein the rotary pump is a multistage pump and the impeller is one of a plurality of impellers.

11. The rotary pump in accordance with claim 1, wherein the impeller is a first stage impeller, and the hydraulic unit further comprises a last stage impeller, with each of the first stage impeller and the last stage impeller fixedly mounted on the pump shaft.

12. The rotary pump in accordance with claim 11, wherein the mechanical seal is arranged adjacent to the last stage impeller with respect to an axial direction.

13. The rotary pump in accordance with claim 1, wherein the mechanical seal is configured to seal against the atmosphere.

14. The rotary pump in accordance with claim 1, wherein the rotor comprises a rotor seal ring having an inner diameter which is at least 20 mm larger than a diameter of the pump.

15. The rotary pump in accordance with claim 1, wherein the rotor comprises a rotor seal ring having an inner diameter which is at least 25 mm larger than a diameter of the pump.

16. The rotary pump in accordance with claim 1, wherein the mechanical seal has a sealing diameter, which is at least 20 mm larger than a diameter of the pump shaft.

17. The rotary pump in accordance with claim 1, wherein the mechanical seal has a sealing diameter, which is at least 25 mm larger than a diameter of the pump shaft.

18. The rotary pump in accordance with claim 1, wherein the impeller is a first stage impeller, and the hydraulic unit further comprises a last stage impeller and an intermediate stage impeller, with each of the first stage impeller, the intermediate stage impeller and the last stage impeller fixedly mounted on the pump shaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The invention will be explained in more detail hereinafter with reference to embodiments of the invention and with reference to the drawings.

[0035] FIG. 1 is a schematic cross-sectional view of an embodiment of a rotary pump according to the invention, and

[0036] FIG. 2 is a more detailed and enlarged cross-sectional view illustrating the mechanical seal.

DETAILED DESCRIPTION

[0037] FIG. 1 shows a schematic cross-sectional view of an embodiment of a rotary pump according to the disclosure, which is designated in its entity with reference numeral 1. The pump 1 is designed as a centrifugal pump for conveying a fluid, for example a liquid such as water.

[0038] The rotary pump 1 comprises a pump housing 2 having an inlet 3 and an outlet 4 for the fluid to be conveyed. The inlet 3 is arranged on a suction side and receives the fluid having a suction pressure SP. The outlet 4 is arranged on a discharge side and discharges the fluid having a discharge pressure DP, wherein the discharge pressure DP is larger than the suction pressure SP. The pump 1 further comprises a hydraulic unit 5 for conveying the fluid from the inlet 3 the outlet 4 and for pressurizing the fluid from the suction pressure SP such that the fluid is discharged at the outlet 4 with the discharge pressure DP. In FIG. 1 the flow of the fluid is indicated by the dashed arrows without reference numerals.

[0039] The pressure prevailing in the environment outside of the pump housing 2 is referred to as ambient pressure AP. The ambient pressure can be the atmospheric pressure. Furthermore, the ambient pressure AP can be essentially the same as the suction SP. However, depending from the particular application, the suction pressure SP can considerably differ from the ambient pressure.

[0040] The hydraulic unit 5 comprises at least one impeller 51, 52, 53 for acting on the fluid.

[0041] The pump 1 further comprises a pump shaft 6 for rotating each impeller 51, 52, 53 about an axial direction A. The axial direction A is defined by the axis of the pump shaft 6. A direction perpendicular to the axial direction A is referred to as a radial direction. The pump shaft 6 extends from a drive end 61 to a non-drive end 62. In this embodiment of the pump the drive end 61 of the pump shaft 6 is located outside of the pump housing 2 and can be connected to a drive unit (not shown) for driving the rotation of the pump shaft 6 about the axial direction A. The drive unit can comprise, for example, an electric motor. Each impeller 51, 52, 53 is mounted to the pump shaft 6 in a torque proof manner.

[0042] In the following description reference is made by way of example to an embodiment, which is suited for many applications, namely that the rotary pump 1 is configured as a multistage pump 1, wherein the hydraulic unit 5 comprises a plurality of impellers 51, 52, 53, namely at least a first stage impeller 51, a last stage impeller 52, and optionally at least one intermediate stage impeller 53, with each impeller 51, 52, 53 fixedly mounted on the pump shaft 6. The impellers 51, 52, 53 are arranged one after another on the pump shaft 6. The reference numeral 51 designates the first stage impeller, which is arranged closest to the inlet 3 for receiving the fluid with the suction pressure SP. The reference numeral 52 designates the last stage impeller 52, which is the impeller 52 closest to the outlet 4. The last stage impeller 52 pressurizes the fluid such, that the fluid is discharged through the outlet 4 with the discharge pressure DP. The reference numeral 53 designates an intermediate stage impeller 53. Each intermediate stage impeller 53 is arranged between the first stage impeller 51 and the last stage impeller 52 when viewed in the direction of increasing pressure.

[0043] The embodiment shown in FIG. 1 has nine stages, i.e. the hydraulic unit 5 comprises the first stage impeller 51, the last stage impeller 52 and seven intermediate stage impellers 53. Of course, the number of nine stages has to be understood exemplary. The plurality of impellers 51, 52, 53 can be arranged in an in-line configuration as shown in FIG. 1 or in a back-to-back configuration. In case of embodiments of the pump 1 as a single stage pump the hydraulic unit is provided with only one impeller constituting the first stage impeller 51 or the last stage impeller 52, respectively.

[0044] The multistage rotary pump 1 shown in FIG. 1 is designed as a horizontal pump, meaning that during operation the pump shaft 6 is extending horizontally, i.e. the axial direction A is perpendicular to the direction of gravity. The rotary pump 1 shown in FIG. 1 is configured without an outer barrel casing, for example as a BB4 type pump. In other embodiments, the rotary pump 1 can be designed as a horizontal barrel casing multistage pump, i.e. as a double-casing pump.

[0045] It has to be understood that the disclosure is not restricted to this types of rotary pump 1. In other embodiments, the rotary pump can be designed for example as a vertical pump, meaning that during operation the pump shaft 6 is extending in the vertical direction, which is the direction of gravity.

[0046] The rotary pump 1 comprises bearings on both sides of the hydraulic unit 5 (with respect to the axial direction A), i.e. the rotary pump 1 is designed as a between-bearing pump. A first radial bearing 81, a second radial bearing 82 and an axial bearing 83 are provided for supporting the pump shaft 6. The first radial bearing 81 is arranged adjacent to the drive end 61 of the pump shaft 6. The second radial bearing 82 is arranged adjacent or at the non-drive end 62 of the pump shaft 6. The axial bearing 83 is arranged between the hydraulic unit 5 and the first radial bearing 81 adjacent to the first radial bearing 81. The bearings 81, 82, 83 are configured to support the pump shaft 6 both in the axial direction A and in a radial direction. The radial bearings 81 and 82 are supporting the pump shaft 6 with respect to the radial direction, and the axial bearing 83 is supporting the shaft 6 with respect to the axial direction A. The first radial bearing 81 and the axial bearing 83 are arranged such that the first radial bearing 81 is closer to the drive end 61 of the shaft 6. Of course, it is also possible to exchange the position of the first radial bearing 81 and the axial bearing 83, i.e. to arrange the first radial bearing 81 between the axial bearing 83 and the plurality of impellers 5, 51, so that the axial bearing 83 is closer to the drive end 61 of the shaft 6.

[0047] In other embodiments the axial bearing 83 can be arranged next to the second radial bearing 82, i.e. next to the non-drive end 62 of the pump shaft 6. In such embodiments the axial bearing 83 can be arranged between the hydraulic unit 5 and the second radial bearing 82 or between the second radial bearing 82 and the non-drive end 62 of the pump shaft 6.

[0048] A radial bearing, such as the first or the second radial bearing 81 or 82 is also referred to as a “journal bearing” and an axial bearing, such as the axial bearing 83, is also referred to as an “thrust bearing”. The first radial bearing 81 and the axial bearing 83 can be configured as separate bearings as shown in FIG. 1, but it is also possible that the first radial bearing 81 and the axial bearing 83 are configured as a single combined radial and axial bearing supporting the shaft both in radial and in axial direction.

[0049] Usually the bearings 81, 82, 83 are provided in separate bearing housings 84, 85, which are fixedly connected to the pump housing 2. The first radial bearing 81 and the axial bearing 83 are arranged in a first bearing housing 84 arranged adjacent to the drive end 61 of the pump shaft 6. The second radial bearing 82 is provided in a second bearing housing 85 arranged adjacent to the non-drive end 62 of the pump shaft 6.

[0050] All bearings 81, 82, 83 are preferably configured as antifriction bearings, such as ball bearings. Of course, it is also possible that some or all bearings 81, 82, 83 are configured as hydrodynamic bearings.

[0051] The rotary pump 1 further comprises two sealing devices, namely a mechanical seal 7, for sealing the pump shaft 6 between the hydraulic unit 5 and the first bearing housing 84, and a second sealing device 8 for sealing the pump shaft 6 at the suction side adjacent to the first stage impeller 51 and the inlet 3. With respect to the axial direction A the second sealing device 8 is arranged between the hydraulic unit 5 and the second radial bearing 82, and the mechanical seal 7 is arranged between the hydraulic unit 5 and the axial pump bearing 83. Both the mechanical seal 7 and the second sealing device 8 seal the pump shaft 6 against a leakage of the fluid along the shaft 6 e.g. into the environment. Furthermore, by the sealing devices 7 and 8 the fluid can be prevented from entering the bearings 81, 82, 83. Preferably, the second sealing device 8 is configured as a second mechanical seal.

[0052] In other embodiments, there is no second sealing device 8 at the non-drive end 62. The second radial bearing 82 is configured as a process fluid lubricated bearing 82, which is also referred to as PLB (process lubricated bearing). The term “process fluid lubricated bearing” refers to a bearing, where the process fluid that is conveyed by the pump 1 is used for the lubrication and the cooling of the bearing 82. The bearing 82 is flooded with the fluid conveyed by the pump 1. Therefore, there is no need for a second sealing device 8.

[0053] Mechanical seals as such are well-known in the art in many different embodiments and therefore require no detailed explanation. The mechanical seal 7 is a seal for the rotating pump shaft 7 and comprises a rotor 76 fixed to the pump shaft 6 and rotating with the pump shaft 6, as well as a stationary stator 77 fixed with respect to the pump housing 2. During operation the rotor 76 and the stator 77 are sliding along each other—usually with a liquid film there between—for providing a sealing action to prevent the fluid from escaping to the environment or entering the bearing housing 84. The second sealing device 8 is configured as the second mechanical seal and comprises a second rotor 86 fixed to the pump shaft 6 and rotating with the pump shaft 6, as well as a stationary second stator 87 fixed with respect to the pump housing 2. During operation the second rotor 86 and the second stator 87 are sliding along each other—usually with a liquid film there between—for providing a sealing action to prevent the fluid from escaping to the environment or entering the bearing housing 85.

[0054] The mechanical seal 7 can be configured according to different well-known configurations, for example as a single mechanical seal or as a double mechanical seal, such as a tandem mechanical seal or a back-to-back mechanical seal.

[0055] For a better understanding FIG. 2 shows a more detailed and enlarged cross-sectional view illustrating the mechanical seal 7.

[0056] In FIG. 2, the centerline M of the pump shaft 6 is shown. The centerline M extends in the axial direction A.

[0057] The rotor 76 of the mechanical seal 7 comprises a rotor seal ring 761 having a annular seal face. The stator 77 of the mechanical seal 7 comprises a stator seal ring 771 having an annular mating face for cooperating with the annular seal face of the rotor seal ring 761. The contact area between the seal face of the rotor seal ring 761 and the mating face of the stator seal ring 771 provides the sealing action during operation of the rotary pump 1. Usually, there is a fluid film on the contact area constituting a lubricant for the relative sliding motion between the rotor seal ring 761 and the stator seal ring 771. The fluid film can consist of the fluid which is conveyed by the rotary pump 1, or a lubricant different from the process fluid conveyed by the pump 1 is supplied to the mechanical seal 7 for forming the fluid film on the contact area, i.e. between the rotating rotor seal ring 761 and the stationary stator seal ring 771. The process fluid or the lubricant also provide for a cooling action to remove the heat which is generated by the relative movement between the rotor 76 and the stator.

[0058] Usually, the rotor seal ring 761 and/or the stator seal ring 771 are spring-loaded to pretension the annular seal face of the rotor seal ring 761 with respect to the annular mating face of the stator seal ring 771. To this end the mechanical seal 7 comprises a plurality of springs (not shown) acting on the rotor seal ring 761 and/or the stator seal ring 771.

[0059] According to the disclosure the mechanical seal is configured as a balancing device for generating an axial force FA acting on the pump shaft 6 during operation of the pump 1, wherein the axial force FA counteracts an axial thrust TA, which is generated by the hydraulic unit 5, in particular by the impeller(s) 51, 52, 53. Usually, each impeller 51, 52, 53 increases the pressure of the fluid, Thus, at the discharge side of each impeller 51, 52, 53 a pressure prevails that is larger than the pressure at the suction side of the same impeller 51, 52, 53. Therefore, each impeller 51, 52, 53 generates an individual axial thrust acting on the pump shaft, wherein the individual axial thrust is directed from the discharge side towards the suction side of the particular impeller 51, 52, 53. All the individual axial thrusts generated by the particular impellers 51, 52, 53 add up to the axial thrust TA indicated in FIG. 2.

[0060] Since the mechanical seal 7 is configured as a balancing device for generating the axial force FA directed in the opposite direction than the axial thrust TA there is no need for a separate balancing device other than the mechanical seal 7, i.e. there is no need for example for a separate balance drum or a separate balance disc as they are known from conventional rotary pumps.

[0061] In the embodiment shown in FIG. 1 and FIG. 2 the mechanical seal 7 has a sealing diameter, which is configured for balancing the axial thrust TA. In FIG. 2 the sealing radius SR of the mechanical seal 7 is shown. The sealing radius SR corresponds to half the sealing diameter. As customary in the art, the sealing diameter of the mechanical seal 7 is the diameter of the midline of the counter running faces of the rotor 76 and the stator 77. Thus, the sealing diameter is the diameter of the midline of the contact area between the seal face of the rotor seal ring 761 and the mating face of the stator seal ring 771. The location of the midline is indicated in FIG. 2 by the dashed line with the reference numeral ML. The sealing radius SR is the distance in the radial direction between the centerline M of the pump shaft 6 and the midline ML. The sealing diameter is two times the sealing radius SR.

[0062] The mechanical seal 7 is arranged adjacent to the last stage impeller 52 with respect to the axial direction A. The mechanical seal 7 has a front side 71. The front side 71 is the side facing the last stage impeller 52 of the hydraulic unit 5. Regarding the axial direction the front side 71 is arranged adjacent to a back side 521 of the last stage impeller 52, so that the front side 71 is exposed to the same pressure that prevails at the back side 521 of the last stage impeller 52. Neglecting minor pressure drops, the pressure prevailing at the back side 521 of the last stage impeller 52 is at least approximately the same as the discharge pressure DP.

[0063] The mechanical seal 7 further comprises a back side 72 which is the side facing away from the last stage impeller 52. As it can be seen in FIG. 1, the back side 72 of the mechanical seal 7 faces the bearing housing 84 or the axial bearing 83. Regarding the axial direction A, an annular chamber 9 is provided next to the back side 72 of the mechanical seal 7, i.e. the annular chamber is arranged between the mechanical seal 7 and the axial bearing 83. Thus, the back side 72 is exposed to the pressure prevailing in the annular chamber 9. Preferably, the pressure prevailing in the annular chamber 9 is the same as the suction pressure SP or the same as the ambient pressure AP, i.e. the environmental pressure prevailing outside the pump housing 2. In the embodiment of the rotary pump 1 described here, the pressure in the annular chamber 9 is at least essentially the same as the ambient pressure AP. The annular chamber 9 can be provided with a drainage opening (not shown) for discharging the fluid leaking along the contact area between the rotor 76 and the stator 77 during operation of the pump 1.

[0064] The axial force FA generated by the mechanical seal 7 results from the different pressures prevailing at the front side 71 and at the backside 72 of the mechanical seal 7. Assuming that the front side 71 is exposed to a pressure which essentially equals the discharge pressure DP and the backside to a pressure which essentially equals the suction pressure SP, the axial force FA depends on the pressure difference DP-SP and on the sealing diameter of the mechanical seal 7. Thus, by means of the sealing diameter of the mechanical seal 7 the axial force FA can be adjusted to such a value that the axial force balances the axial thrust TA generated by the hydraulic unit 5 during operation of the pump 1. The balancing can be a complete balancing of 100% or a balancing of less than 100%.

[0065] For example, the sealing diameter of the mechanical seal 7 can be configured such, that is corresponds to the diameter of the relief passage between the balance drum and the surrounding stationary part, if the same pump were configured according to the conventional design with a separate balance drum. In other words, the rotary pump according to the disclosure can be configured by removing the balance drum of a conventional rotary pump and configuring the mechanical seal 7 with the sealing diameter, which equals the diameter of the relief passage extending along the balance drum in the conventional design.

[0066] Thus, when dimensioning the mechanical seal 7 of the rotary pump 1, in particular with respect to the sealing diameter of the mechanical seal 7, the same methods, procedures or calculations can be used as they are used for dimensioning a balance drum in a conventional pump.

[0067] For many applications it is preferred that the sealing diameter is at least fifteen millimeter larger than the diameter of the pump shaft 6 at the location where the rotor 76 is arranged.

[0068] For many applications it is also preferred that the sealing diameter is at least twenty millimeters or even at least twenty-five millimeters or even thirty millimeters larger than the diameter of the pump shaft 6 at the location where the rotor 76 is arranged.

[0069] Furthermore, from the praxis it became apparent that for many applications the rotor seal ring 761 preferably has an inner diameter, which is at least fifteen millimeter larger than the diameter of the pump shaft 6 at the location where the rotor 76 is arranged.

[0070] For many applications it is also preferred that the rotor seal ring 761 has an inner diameter, which is at least twenty millimeters or even at least twenty-five millimeters or even thirty millimeters larger than the diameter of the pump shaft 6 at the location where the rotor 76 is arranged.

[0071] In FIG. 2 the inner radius IR of the rotor seal ring 761 is indicated. The inner radius IR is half the inner diameter of the rotor seal ring 761.

[0072] The preferred difference between the sealing diameter and the diameter of the pump shaft 6, or between the inner diameter of the rotor seal ring 761 and the pump shaft 6, respectively, depends on the particular application. Based on practical experience, for a diameter of the pump shaft 6, which is less or up to 120 mm, the sealing diameter or the inner diameter of the rotor seal ring 761, respectively, is preferably at least 15 mm larger than the diameter of the pump shaft 6. For a diameter of the pump shaft 6, which is larger than 120 mm the sealing diameter or the inner diameter of the rotor seal ring 761, respectively, is preferably at least 20 mm, or even at least 25 mm larger than the diameter of the pump shaft 6.

[0073] Particularly for pump shafts having a large diameter, it can be advantageous that the sealing diameter or the inner diameter of the rotor seal ring 761, respectively, is preferably at least 30 mm larger than the diameter of the pump shaft 6.

[0074] Optionally, a disaster bushing 10 can be provided for restricting the leakage of the fluid through the mechanical seal in the event of a failure of the mechanical seal 7. The disaster bushing 10 can be arranged at and fixed to the stator 77 of the mechanical seal 7. The disaster bushing 10 surrounds the rotor 76 with a small clearance and is located adjacent to the annular chamber 9.

[0075] In principle, the mechanical seal can be configured according to all known designs for mechanical seals. In particular, the mechanical seal 7 can be configured as a double mechanical seal 7, e.g. in a tandem configuration or in a back-to-back configuration or in a face-to-face configuration.