Self-priming centrifugal pumps
United States Patent [191 Speck et al.  
 [ Apr. 15, 1975 SELF-PRIMING CENTRIFUGAL PUMPS [75] Inventors: Walter Speck; Oskar Schmidt, both of Hilpoltstein, Germany [73] Assignee: Speck-Pumpen Daniel Speck &amp;  
 Sohne, I-lilpoltstein, Germany 22 Filed: Nov. 26, 1973 211 App]. No.: 419,149  
 [30] Foreign Application Priority Data Sept. 24, 1973 Germany 2347915 [52] U.S. Cl 415/53; 415/207 [51] Int. Cl. F04d 5/00 [58] Field of Search 415/53, 148, 159, 26, 211,  
 [5 6] References Cited UNITED STATES PATENTS 902,605 11/1908 Reeve ..415/26 1,439,365 12/1922 Hazel] 415/53 1,604,328 10/1926 Walker 415/148 1,936,771 11/1933 Schellens 415/169 2,224,615 12/1940 Stratton 415/53 FOREIGN PATENTS OR APPLICATIONS 525,278 8/1940 United Kingdom 415/53 Primary Examinerl-lenry F. Raduazo Attorney, Agent, or Firm-Steinberg &amp; Blake [57] ABSTRACT A self-priming centrifugal pump having an inlet leading to a rotary impeller which has a given axis of rotation. The impeller is surrounded by a fluid guide which is located in a housing provided with an outlet through which fluid is discharged from the pump. The fluid guide is formed with a gap situated in a plane which is perpendicular to the above axis so that during self-priming operations liquid can return back toward the axis of the impeller through the latter gap.  
 6 Claims, 2 Drawing Figures SELF-PRIMING CENTRIFUGAL PUMPS BACKGROUND OF THE INVENTION The present invention relates to pumps.  
  In particular. the present invention relates to centrifugal pumps. and more specifically. to self-priming centrifugal pumps.  
  As is well known. centrifugal pumps must be primed during the initial starting operations so as to eliminate air from the interior of such pumps. Thus. self-priming centrifugal pumps capable of forming in their interiors a mixture of air and liquid are used for pumping liquids. With pumps of this type in addition to providing a high efficiency it is also desired to provide a short priming time. In addition. it is highly desirable to maintain at a minimum the wear resulting from erosion by the liquid and non-uniform loading in the region of the impeller chamber as a result of the liquid action during selfpriming operations.  
  The state of the art indicates that self-priming centrifugal pumps with interior liquid-air mixtures have long been known. The flow of air out of the pump is brought about by mixing liquid which is present in the impeller with air from the suction inlet with this mixture being delivered through a fluid-guide into the pressure chamber ofthe pump. In the latter chamber the air separates itself from the liquid and discharges through the outlet of the pump. The liquid. on the other hand. returns along a circular or closed path to the region of the impeller. The fluid-guide takes the form either of a tubular spiral with one or two vanes or of a ring having vanes uniformly distributed.  
  Suitable passages must be provided in order to return the circulating self-priming liquid at a favorable speed and direction. Thus. it is conventional to provide for this purpose one or more openings in the wall which separates the impeller chamber from the pressure chamber in the pump housing. The arrangement of these openings can vary widely. However in many pumps passages are situated in the region of the impeller vanes. while in other pumps they are situated beyond the periphery of the impeller. It is also conventional to connect a branch conduit to the spiral or volute. this conduit making possible the return of the circulating priming liquid during conveying of air out of the pump when the priming operations are going forward.  
  The great disadvantage of constructions of the above type resides in the fact that the circulating priming liquid is returned only to a predetermined part of the impcller. As a result a non-uniform loading occurs and the impeller. the impeller shaft. and the bearings are undesirably stressed with large loads.  
  Other known pumps have a fluid-guiding structure in the form of several vanes arranged on a circular ring. With such constructions the pumping passages must also be used for the return of the circulating priming liquid or with such constructions it is also known to provide special passages for this purpose. The stream of circulating priming liquid quickly brings about an extensive erosion at the impeller vanes and in the region of the return openings at the pump housing. This undesirable rapid erosion is intensified in the case where impurities are carried along with the fluid. A further disadvantage of this type of construction resides in the fact that it is possible for the return openings or passages to become easily stopped up. and there is an unavoidable loss of efficiency inasmuch as during the liquid pumping operation. subsequent to the priming operation. the liquid continues to flow along the circular or closed path which the priming liquid follows during the priming operations. In addition. with constructions of this type it is frequently essential to provide the pump with an extremely and undesirably large size. resulting in a requirement of a large space to accommodate the pump.  
 SUMMARY OF THE INVENTION lt is accordingly a primary object of the present invention to provide a self-priming centrifugal pump which will avoid the above drawbacks and which will improve the manner in which the self-priming operations are carried out.  
  Also it is an object of the present invention to provide a centrifugal pump with the capability of carrying out the priming operations in an extremely short time.  
  Furthermore. it is an object of thepresent invention to provide a self-priming centrifugal pump which is capable of eliminating or at a minimum sharply reducing undesirable operating characteristics such as unbalanced loads, rapid wear of the pump components. and possibility of plugging passages with foreign matter.  
  It is also an object of the present invention to provide a self-priming centrifugal pump which terminates the flow of liquid in the direction it takes during the selfpriming operations so that the efficiency of the pump is not reduced by maintaining liquid flowing in the same way subsequent to priming operations as during the priming operations.  
  It is also an object of the present invention to provide a self-priming centrifugal pump which is capable of achieving all of the above objects while at the same time having a simple rugged construction which is highly reliable in operation.  
  According to the invention the self-priming centrifugal pump has an inlet means through which fluid enters to a rotary impeller means which has a predetermined axis of rotation. A fluid guiding means extends circumferentially around the rotary impeller means to receive the fluid therefrom, and a housing means houses the fluid guiding means and is provided with an outlet through which pumped fluid is discharged. In accordance with the invention the fluid-guiding means is formed with a gap situated in a plane which is perpendicular to the impeller axis. Through this gap it is possible for the self-priming liquid to return in all directions toward the impeller axis.  
 BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:  
  FIG. I is a schematic partly sectional elevation of a pump according to the present invention. the section of FIG. I being in a plane which contains the pump axis; and  
  FIG. 2 is a fragmentary sectional illustration of another embodiment of the pump of the invention.  
 DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. I. the self-priming centrifugal pump illustrated therein includes a housing means 1 fluid-tightly accommodating in its interior an inner housing portion 2 as well as an inner fluid-guiding means which in the illustrated example takes the form of a volute means 3. Normally. in a conventional pump. the volute means 3 and the inner housing unit 2 would form a unitary structure fluid-tightly accommodated in the interior of the housing I by way of sealing rings 13 and 14. However. in accordance with the invention. the volute means 3 is in its outer wall with an outer gap 4. so that the volute means includes in the illustrated example a pair of sections separated from each other by the outer gap 4. A rotary impeller means 5 is also accommodated in the interior of the housing means I. this rotary impeller means 5 being carried by a drive shaft I1 driven from any suitable motor and having an axis coinciding with the axis of rotation of the impeller means 5. Along this axis the housing means 1 is formed with the suction inlet 8 through which fluid enters the pump to be received at the central inlet in the impeller means 5. The outer gap 4 in the illustrated example may have a width of approximately I mm. and it extends completely through the entire volute means along the entire contour thereof. It will be seen that the volute means 3 has directly next to the outer periphery of the impeller means 5 an inner circumferential gap substantially wider than the outer gap 4 which is situated in a plane which extends midway through the inner gap as well as through the outer periphery of the impeller means 5 substantially midway between the outer circumferential end edges of the impeller means 5. Moreover it will be seen that the hollow interior ofthe volute means 3 has in a direction parallel to the axis of the impcller means 5 a width which at a minimum is equal to the width of the inner gap and which over most of the length of the volute means 3 is substantially wider than the inner gap. A means is provided for determining the width of the gap 4, and in the example of FIG. 1 this means takes the form of a plurality of projections 10 carried by one of the sections ofthe volute means 3 and extending across the gap 4 into engagement with the other of the sections. A minimum of three of these spacer projections 10 are provided. distributed at a considerable distance from each other along the volute means 3. and these projections 10 which in the illustrated example determine the width of the gap 4 are so small with respect to the total length of the gap 4 along the contour of the volute means 3 that for practical purposes the entire gap 4 may be considered as being uninterrupted. Thus. by way of these spacer elements 10 the uniform width of the gap 4 is maintained.  
  The housing means 1 defines a collecting chamber 7 in its interior in which fluid is collected prior to discharge out of the pressure outlet 9. The driving motor carries a flange 12 on which the pump structure is mounted as illustrated. The fluid-guiding means formed by the volute means 3 has an outlet 6 communicating with the interior of the collecting chamber 7.  
  During the priming operations. when the pump is started. the liquid which is present in the impeller means 5 is thrown by centrifugal force through the inner relatively wide circumferential gap of volute means 3 into the volute means 3 to discharge through the outlet 6 thereof into the collecting chamber 7 of the pump housing. The suction pipe of the pump is connected to the suction inlet 8. From the latter. air which enters into the pump when the latter is started is mixed with the liquid present in the pump and is delivered with this liquid into the collecting chamber 7. At the chamber 7 the air separates itself from the liquid and.  
 discharges outthrough the pressure outlet 9 which also may be connected to a suitable discharge conduit. At the same time the liquid from which the air has become separated returns through the gap 4 into the impeller where this liquid again mixes with air priming operations.  
  In this manner the self-priming takes place with the air which is present at the starting of the pump being automatically removed in an extremely short time so that after this short time the normal pumping operations can go forward with pumping only of liquid. Thus. after a short period of time only liquid will enter through the suction inlet 8 into the impeller means 5. This liquid which is sucked into the pump during the normal pumping operations discharges from the volute means 3 through the outlet 6 thereof and ispumped out through the outlet 9 after being received in the chamber 7. During this normal pumping operation. the liquid:  
 no longer flows through the gap 4 toward the axis of the impeller means 5 but instead flows only in a direction away from the axis of the impeller through the gap 4 into the chamber 7. Thus. during the normal pumping operations the flow of liquid through the gap 4 is the reverse of the direction of flow itself thereof through the gap 4 during the priming operations. Thus. during normal pumping operations with the pump of the. invention the pumped liquid will reach the chamber 7 not only from the outlet 6 of the volute means 3.but also from the gap 4.  
  Other constructions are possible. instead of the spacer means I0. in order to determine the. width of the gap 4. Thus. FIG. 2 shows an embodiment of the invention where a connecting means connects the separated sections of the volute means 3 to the housing means 1 in order to determine the width of the gap 4. Thus. as is illustrated in FIG. 2. this connecting means may take the form of a plurality of rods 20 connected with the separate sections of the volute means 3. FIG. 2 illustrates one rod 20 connected to each of the sections of r the volute means 3. These rods 20 may be formedintegrally with the volute sections. At their outer ends. the  
 rods 20 engage the inner surface of the housing I. and  
 suitable bolts. screws. or the like. such as the illustrated screws 22, extend through suitable openings of the housing I into threaded bores of the rods 22 in order to fix the latter to the housing 1. In this way the connecting means 20 fixes the separated sections of the volute means with respect to the housing 1 so as to determine the width of the gap 4.  
  With the above-described structure of the invention. the circulating priming liquid is capable of returning toward the pump axis. in a substantially radial direction toward the center of the impeller thus engaging the vanes thereof and entering deep into the spaces between the vanes toward the impeller axis. It willbe noted that the plane in which the gap 4 is located is not only perpendicular to the axis of the impeller means 5 but also the periphery of the impeller means 5 extends through this plane. The liquid which returns toward the impeller axis during the priming operations is capable of flowing in all directions in the plane of the gap 4 inwardly toward the impeller axis. As a result. during the self-priming operations the impeller means is at all times uniformly loaded at its entire periphery with the circulating priming liquid. so that with the pump of the invention the priming liquid is utilized in a far superior to repeat these manner than has been the case heretofore for the purpose of conveying air out of the pump. and in this way a considerable reduction in the time required for the priming operations is achieved. Moreover. the uniform centralized loading of the impeller means reduces the extent to which wear takes place from the liquid. and if foreign bodies or other impurities are present. the extent to which the structure will be worn by such foreign matter is also reduced. In addition. the undesirably excessive loading of the impeller. the impeller shaft. and the bearings. as is present with known constructions. is reduced to a very large extent. so that with the construction of the invention the wear which results from the operating conditions is greatly reduced.  
  In the event that impurities in the form of any foreign bodies or the like are present. they will be prevented from returning with the circulating priming liquid toward the impeller axis beyond the gap 4 as long as the size of the impurities is large enough to prevent the impurities from passing through the gap 4. It is precisely such impurities which bring about increased wear and damage of the impeller vanes with increasing size of the impurities. as experience has demonstrated. Possible plugging or stopping up of passages. which might occur due to the presence of fiber impurities in the pumped fluid. is reliably avoided since there is no possibility for such impurities to become situated at the gap. As was pointed out above. when the normal pumping operation starts immediately after the priming operation. the flow of liquid through the gap 4 is reversed so that any impurities which have deposited themselves at the gap 4. at the exterior of the volute means 3. are washed away from the gap 4 as a result of the reversal in the flow of liquid. so that self-cleaning of the gap 4 takes place.  
  The width of the gap 4 may range between approximately 0.5 and 5 mm. The particular choice of a specific width for the gap 4 will depend upon the fluid which is pumped and the speed of rotation of the impeller means. so that the pump designer with a knowledge of the present invention can without difficulty select for a particular pump construction and design the optimum gap width. As was indicated above in connection with FIG. 1, it is possible to maintain a uniform width of the gap by the spacer means 10, while. if desired. other constructions may be utilized for this purpose as. for example. by way of a connecting means which connects the fluid-guiding means 3 to the housing means 1, this connecting means being shown in FIG. 2 as taking the form of the rods 20 described above.  
  Because the flow of priming liquid is terminated after the air has been discharged out of the pump, there is no loss of efficiency. as contrasted with conventional selfpriming centrifugal pumps which are known in the art.  
 What is claimed is:  
 1. In a self-priming centrifugal pump. rotary impeller means having a given axis of rotation. at central suction inlet. and an outer peripheral outlet circumferentially surrounding said axis. fluid-guiding means situated at the periphery of said impeller means and being in the form of a hollow volute means formed with an inner relatively substantially constant width axial gap circumferentially surrounding and situated directly next to the periphery of said impeller means for directly receiving fluid therefrom. the hollow interior of said volute means being substantially wider than said inner gap along substantially all of the length of said volute means with the hollow interior of said volute means extending axially in both directions beyond said inner gap of said volute means. and said volute means having an outer wall formed in a plane perpendicular to said axis and through which said outer periphery of said impeller means extends with an outer relatively narrow axial gap extending substantially through the entire length of the outer wall of said volute means and through which liquid can return toward said axis during self-priming operations. and a housing means housing said impeller means and said volute means which is formed with said outer gap in said plane. said housing means having an outlet through which fluid from said volute means is discharged while liquid can return toward said axis during self-priming operations through said gaps in said volute means.  
  2. The combination of claim 1 and wherein said outer gap has a width of 0.5 to 5 mm.  
  3. The combination of claim 1 and wherein said volute means includes a pair of volute sections which are separated from each other at said gaps. and spacer means distributed along said outer gap at a small number of locations and situated between said sections for determining the width of said gap.  
  4. The combination of claim I and wherein a connecting means connects said volute means to said housing means for determining the width of said gaps.  
  5. The combination of claim 1 and wherein said volute means includes a pair of sections separated from each other by said gaps. and means operatively connected with at least one of said sections for determining the position thereof along said axis with respect to the other of said sections for determining the width of said gaps;  
 6. The combination of claim 1 and wherein said hous-&#39; ing means defines a chamber in which said outer gap is located; so that during self-priming operations liquid will return from said chamber toward said axis in one direction through said outer gap while subsequent to self-priming operations liquid will flow from said impeller means through said outer gap into said chamber and out of said housing means through said outlet thereof in .an opposite direction through said outer gap.  
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