Axial pressure balancing arrangement for a multistage centrifugal pump
United States Patent Hanagarth Apr. 1, 1975 AXIAL PRESSURE BALANCING 1,151,964 8/1915 Peterson 415/106 AR NG FOR A MULTISTAGE 1,151,965 8/1915 Peterson 415/106 1,609,306 12/1926 Peterson 415/106 CENTRIFUGAL PUMP 1,642,914 9/1927 Whann 415/501 [75] Inventor; Wolfgang Hanagarth, Frankenthal, 2,857,850 10/1958 Tsiguloff 415/501 Pfal Germany Norqurst 3,438,330 4/1969 Evans 415/53 [73] Assignee: Klein, Schanzlin &amp; Becker Aktiengesenschaft Frankenthal, FOREIGN PATENTS OR APPLICATIONS Pfalz, Germany 276,593 7/1914 Germany 415/53 2,483 1909 United Kingdom 415/106 Flledl 17, 1972 205,189 12/1908 Germany 415/106 21 App]. No.: 281,546  
  Primary Examinerl-lenry F. Raduazo [30] F A r r P t D t Attorney, Agent, or FirmMichael S. Striker orergn pp rca ion rlorl y a :1 Aug. 21, 1971 Germany 2141966 [57] ABSTRACT A plurality of rotors alternate with stator portions to g form therewith gaps in which throttle portions, such as [58] Field &#34;A 106 107 a circular recess cooperating with a circular projec- 415/501 tion, are provided. Axial ducts connect the inlet of each rotor with the inner part of the gap, whose outer [56] References Cited part communicates with the outlet of the rotor. The  
  axial force acting on the rotors is balanced by an op- UNITED STATES PATENTS posite axial force produced by the inward stream 958,612 5/1910 Eyermann 415/106 through the gap, until the stream is throttled by the axial movements of the rotors.  
 1,105:808 8/1914 415/106 3 Claims, 6 Drawing Figures PAH-INTER APR 1 ms sum 2 of 4 Fig. :2  
 . ATEHTEBAFR 1 W5 saw 3 or 4 Fig. :5  
 AXIAL PRESSURE BALANCING ARRANGEMENT FOR A MULTISTAGE CENTRIFUGAL PUMP BACKGROUND OF THE INVENTION Multistage centrifugal pumps, as are used, for example, as feeding pumps for boilers having a very great pressure head, develop a pronounced axial force which is generally hydraulically balanced by an additional device. such additional balancing device may include relief pistons which require an additional thrust bearing for the remaining axial forces, or relief discs which automatically balance the axial force acting on the rotors of the pump. Combinations of such constructions also require an additional axial thrust bearing to control certain axial forces.  
  The relief devices according to the prior art perform the desired function to a certain degree, but have the disadvantage of a complicated structure which increases the cost and the axial length. Also a substantial loss in efficiency occurs due to the flow losses in the relief device caused by a friction at the endfaces of the relief device. The wear upon the relief device is quite pronounced due to the high pressure differential, and also the mechanical reliability, when pump distortion or rotor bending occurs, is unsatisfactory.  
  The conventional relief devices have the disadvantage that the limit of automatic regulation is located at a value not much greater than Q/Q I :3 to 1:4 which when the pump is operated under an overload, as may occur upon a pipe break or another disturbance, frequently results in jamming of the relief device and destruction of the pump.  
 SUMMARY OF THE INVENTION It is an object of the invention to overcome the disadvantages of known axial pressure relief arrangements for centrifugal pumps, and obtain balancing of the axial forces at each stage of a multistage centrifugal pump.  
  Another object of the invention is to provide a simple and inexpensive axial pressure balancing arrangement using a duct through each rotor, and a throttle controlling the branch flow through the gap between a rotor and the adjacent stator portion.  
  With these objects in view, a multistage centrifugal pump with a plurality of rotors and stator portions between the rotors is provided with gaps between the rotors and stator portions whose width varies depending on the rotor position, and which is arranged in series with one or several relief openings or ducts at each rotor. The arrangement requires only normal tolerances for the several rotors, because the total axial pressure equalization occurs even if the widths of the several gaps differ. The multistage centrifugal pump according to the invention has substantial advantages, for example the elimination of a separate relief device, and thereby the possibility to obtain a short, compact, reliable and inexpensive pump, as well as an increase in efficiency as compared with pump provided with known relief devices. Such improvement of the pump is due to the elimination of friction at the endfaces of the relief devices, and also to the reduction of the endface friction of the several rotors which, according to the invention, are used as relief device. The endface friction is reduced due to the fact that the relief flow flows inwards in radial directions through the gap, while in the prior art the flow takes place outward in the space adjacent the rotor endface, which causes an increased friction on the endfaces. Another advantage is the automatic relief of the axial pressure forces up to the highest flow at H= O(mFe.S.), which occurs at Q/Q 2 without further auxiliary devices such as thrust bearings.  
  Another advantage of the invention is the increase of the Lomakin forces in the clearances between the rotor shaft and the stator bores of the respective stator portion which results in a better centering of the rotors, and eliminates the necessity for a radial bearing in the middle of a multistage centrifugal pump. Such an additional bearing in accordance with the prior art, requires space corresponding to an additional rotor and pump stage. The danger of wear is reduced in the arrangement of the invention since not the entire end pressure is used for balancing the axial force produced by one stage. The increase of the width of the control gaps, as compared with construction of the prior art using relief discs, is another object of the invention.  
  The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved pump itself, however, both as to its construction and its make of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments when read in connection with the accompanying drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary axial sectional view illustrating an embodiment of the invention;  
  FIG. 2 is a fragmentary sectional view illustrating on an enlarged scale, a modification of the embodiment of FIG. 1;  
  FIG. 3 is a fragmentary axial sectional view illustrating another modification;  
  FIG. 4 is a fragmentary axial sectional view illustrating another modification;  
  FIG. 5 is a fragmentary axial sectional view illustrating another modification; and  
  FIG. 6 is a fragmentary axial sectional view illustrating another embodiment of the invention.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS:  
  FIG. 1 illustrates an embodiment of the invention in which a multistage centrifugal pump has stator means 20 consisting of several parts held together by bolts 21A and supporting a shaft 22 for rotation. Two rotors I have inner hubs 30 surrounding shaft 22. A first stator portion 21 is disposed between the two rotors 1 and has a sleeve 31 surrounding shaft 22. Stator 20 has an inlet 23 and an outlet 24, and a fluid flows into the inlet la of the first rotor 1 and from the outlet lb in outward direction and is then guided by the first stator portion 21 into the inlet 1a of the next following rotor l, and discharging the fluid from the outlet 1b of the second rotor into a second stator portion 21.  
  The front face on the left of each rotor 1 is adjacent to the rear the respective of each stator portion 21 and forms a gap 5 therewith. Radially outward of its hub 30, each rotor 1 is formed with at least one but preferably a plurality of axially extending ducts 2 each of which connects the inlet la of one rotor 1 with the radially inner part of a gap 5 formed between the front face of rotor 1 and the rear face of the next following stator portion 21. The front face of each rotor l is provided with a circular recess 3 confronting a circular projection 4 on the rear face of the respective stator portion 21. Axially extending stator ducts 7 connect the inner part of each gap with the inlet of the next following rotor 1. Preferably, each duct 7 is located in the respective stator portion 21 adjacent the stator sleeve 31. When a rotor 1 is moved toward a stator portion 21, the circular projection 4 enters the circular recess 3, acting as a throttle. Therefore, parts 3 and 4 may be considered as throttling portions of each rotor and .corresponding stator portion 21.  
  It will be understood that it is possible to provide the projection 4 on the front face of the respective rotor l, and a recess 3 on the rear face of the respective stator portion 21. In the arrangement of FIG. 1, each rotor 1 is relieved and its own pressure head acts in the throttling portions 3 and 4.  
  During operation of the multistage pump shown in FIG. 1, the rotors 1 are displaced to the right in the direction of the arrow A due to the prevailing axial forces caused by the change of direction of the fluid between the inlet 1a and outlet 1b of each rotor 1. Consequently, the width of each control gap 5 is increased so that water flows from the outlet lb of each rotor into the outer part of the respective gap 5 and radially inward through gap 5, past the throttling portions 3 and 4, and through the relief ducts 2 into the respective inlets 1a of the rotors 1. Due to the radial inward flow of the relieving streams in gaps 5, the water of the streams is accelerated in accordance with the constant factor Cu.r, so that the static pressure is reduced in each gap 5 which brings about a resultant axial force acting on the rotors 1 in the direction B, opposite to the direction A, until the front and rear faces of the rotors and stator portions 21 have approached each other to such an extend that the circular projection 4 enters the circular recess 3, acting as a throttle which throttles the stream of relieving water in gap 5 until the axial forces are balanced.  
  The relieved water flowing through the gaps 5 excites the vortices in the gaps 5 to such an extent that the relative speed between the front faces of the rotors 1 and such vortices becomes smaller, resulting in a substantial reduction of the friction losses on the front faces of the rotors, as compared with the arrangements of the prior art in which the branch stream flowing through gap 5 moves outward in gap 5, braking the vortex at the front face of the rotor, which results in a greater relative speed between the front face of the rotor and the vortex adjacent thereto in gap 5, bringing about greater friction losses, irrespective of the increased axial force due to the slower rotation of the vortex.  
  While in the embodiment of FIG. 1, the relie-fducts 2 are located radially inward of the recesses 3, the modification of FIG. 2 positions the relief duct 2 at the same radial distance as the circular throttling recess 3 so that the duct 2 opens into the recess 3. In this arrangement, the branch stream flowing through the stator duct 7 is also regulated by the throttle 3, 4 if it is not required for obtaining greater radial forces, as in the embodiment of FIG. 1.  
  FIG. 3 illustrates another modification in which the relief duct or ducts 2 directly open into the circular recess 3 which has a rectangular cross section, as in the embodiments of FIGS. 1 and 2. However, the circular projection 4 is differently constructed, and has a radial inner face 4a sliding on a complementary face in the recess 3, and at a greater radius a regulating edge 4b. which is spaced from the corresponding face and edge in recess 3. The regulating edge 4b effects an automatic.  
 balancing of the axial forces, and the throttling face 4a 1 has the effect of reducing the flow out of the stator duct 7.  
 In the embodiment of FIG. 4, the relief duct or ducts 2 also open into the circular recess 3 which cooperates with a circular projection 4 to form a throttle. Addi-. tionally, bores 8 are provided at the inner end of the rotor 1 to connect the inner part of gap 5 with the inlet 1a of rotor 1 and cooperating with the stator duct 7 so I that fluid can flow through stator duct 7 and bores 8, as indicated by arrows. The communication between stator ducts 7 and rotor bores 8 is continuous in the arrangement of FIG. 4. The branch stream through gap 5 is substantially independent of the regulation of the axial forces. In the embodiment of FIG. 3, the rotor 1 may also be provided with an open bore or duct 8, as shown in FIG. 4, so that the branch stream is practically independent of the balancing of axial forces, and can be regulated in accordance with the diameters of bores 8.  
 FIG. 5 illustrates an embodiment of the invention in.  
 which a throttling portion 9a at the radially inner end of the front face 9 of the rotor 1 cooperates with a throttling portion at the radially inner end of rear face 10 of stator portion 21.  
 During rotation, the throttling portions 10a and 9a engage each other so that the relief ducts 2 are more or less closed resulting in an automatic balancing of the axial forces. An advantage of the arrangement of FIG.  
 5 is a more rigid regulation than in the arrangement of FIGS. 1 to 4, but requires precise tolerances for the throttling face portions 9a and 10a, which is difficult to obtain for high rotary speeds so that the modification of FIG. 5 should mainly be used for pumps having a small number of rotors.  
  FIG. 5 further shows a rotor duct 7, and also two circular grooves 11 having semicircular cross sections and confronting each other to form a circular conduit.  
 In the embodiment of FIG. 6, the outlet 1b of each rotor is connected by a conduit 25 of respective stator portion 21 with the inlet 1a of the next following rotor. Only the first rotor 1 is provided with a relief duct 2 as described with reference to FIG. 1. Rotors 40 and 41 have hub portions formed with axial channels 6a com,- municatin g with the inner parts of gaps 5. The channels 6a are aligned with channels 6 in the inner surfaces of I sleeve portions 31 within the stator portions 21. In this manner, ducts 2&#39; are formed adjacent the outer surface of shaft 22, and may be angularly staggered about the periphery of shaft 22. The channels or ducts 2&#39; take the place of the relief ducts 2, but the first rotor 1 may be constructed as described with reference to FIG. 1. A  
 further rotor 42 is shown between the rotors l and 41. r  
  The embodiment of FIG. 6 is advantageous if additional weight acts in axial direction, for example if the pump has a vertical axis and the rotor weight is effective in axial direction. The arrangement of FIG. 6 is also advantageous for extending the limits of relief for high speed rotors.  
  It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of balancing arrangements for centrifugal pumps differing from the types described above.  
  While the invention has been illustrated and described as embodied in an axial pressure balancing arrangement for a multistage centrifugal pump, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
  Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of the invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.  
  What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.  
 I claim:  
  1. In a multi-stage centrifugal pump, a combination comprising a hollow stator; a shaft rotatably mounted in said stator; a pair of axially movable coaxial rotors mounted in said stator adjacent to each other and being driven by said shaft, each of said rotors having a fluidadmitting inlet nearer to and a fluid-discharging outlet more distant from said shaft and the inlet of one of said rotors being in communication with the outlet of the other of said rotors, each of said rotors defining with said stator a gap extending radially inwardly from and communicating with the respective outlet; and channel means extending from the gap between said stator and said one rotor to the inlet of said other rotor to convey fluid from said last-mentioned gap into said lastmentioned inlet, each of said rotors defining with said stator discrete throttling means for restricting the flow of fluid in the respective gap to an extent which varies in response to changes in the axial position of the respective rotor.  
  2. A combination as defined in claim 1, wherein each of said throttling means comprises a circular groove in the respective rotor and a circular projection provided on said stator and registering with the respective groove.  
  3. A combination as defined in claim 1, further comprising a sleeve rotatably mounted in said stator between said rotors, said channel means including a portion provided in said sleeve.