Gear pump
United States Patent [191 Svensson Apr. 8, 1975 i 1 GEAR PUMP 148L560 9 1949 Bakewell 4l8/70 3,4 2 S h&#39; 1 1 Inventor: Sven Hiding Svensson. Lund. R1330? 2532? N222??? 4.8m  
 Sweden [73] Assignee: Alia-Laval AB, Tumba, Sweden primary J Husar [32] p Aug 20 1973 Assistant Examiner-O. T. Sessions Attorney, Agent, or FirmCyrus S. Hapgood [2]) Appl. No: 389,584  
 [30] Foreign Application Priority Data [57] ABSTRACT Aug. 1 72 S eden l075 /72 Means are provided to permit relative axial displacement between one of the two gear wheels and a wall [52] US. Cl t. 418/169; 418/181 of the pump chamber, whereby the sealing engage- [5 I] it 6 6 ment between this wheel and wall is interrupted, A de- [58] Fi ld f Search 418/2 0. 81. 9, vice is operable independently of above-normal prcs- 4l7/430; 425/225. 227 sure in the pump chamber to effect this displacement and thereby establish a free passage through the pump [56] References Cited chamber.  
  UNITED STATES PATENTS M72357 6/1928 Heitz 418/70 6 Clams 3 Draw figures A 17 2O 15 2 9a n z2 27 as GEAR PUMP The present invention relates to a gear pump comprising a pump housing having a pump chamber provided with fluid inlet and outlet means, and two gear wheels rotatable around parallel axes within said pump chamber, said gear wheels being adapted during normal operation of the pump to sealingly engage the walls of the pump housing and having intermeshing teeth or similar elements.  
  Pumps of this kind are used, for example, when a vis cous fluid is to be conveyed through a conduit, as in ice-cream or margarine producing plants.  
  A problem which has long been of interest in plants comprising gear pumps, especially within the food industry, is that the cleaning of the plants has been made more difficult, particularly due to the presence of the pumps. That is, gear pumps have a relatively small capacity which, without special arrangements, makes it impossible to flush cleaning liquid through the plant at a sufficient rate to obtain an efficient cleaning thereof.  
  Heretofore, the flushing of cleaning liquid through such a plant has been made possible by removing the gear wheels from all of the gear pumps of the plant. However, this has required extra manual labor, which has been time consuming and has required specially trained personnel. Another solution of the cleaning problem is to provide the gear pumps with by-pass conduits adapted to open when the plant is to be flushed through with cleaning liquid. However, known plants comprising such by-pass conduits have not fulfilled the demands of hygiene raised in the food industry, be cause the by-pass conduits have formed spaces in which the treated product has been kept stationary during the normal operation of the plant, and thus growth of bacteria has been possible.  
  The principal object of the present invention is to eliminate the above-noted problem and to provide a gear pump arrangement which in a simple way enables plants comprising gear pumps to be cleaned efficiently.  
  The invention is characterized by a device which is adapted, independently of a pressure in the pump chamber exceeding the normal operating pressure, to provide for an axial relative displacement of at least one of the gear wheels and one of the walls of the pump chamber, whereby the sealing engagement between these members displaced in relation to each other is interrupted and a free passage is established through the pump chamber, said passage permitting a generally free flow of fluid through the pump chamber between its inlet and outlet. The arrangement for sealing between the portions of the pump housing can be designed in different ways within the scope of the invention. The pump housing portions are preferably so designed that one of them sealingly surrounds the other one, whereby ordinary sealing rings can be used.  
  The invention is applicable to different types of gear pumps and is based on the idea of creating a leakage past the gear wheels within the walls of the pump housing when cleaning is to be carried out, such leakage being prevented during the normal operation of the pump. There are gear pumps of a first type in which both gear wheels have radially outwardly directed teeth, and of a second type having a big gear wheel in the form of a rim having radially inwardly directed teeth, a small gear wheel eccentrically disposed therein and having radially outwardly directed teeth, and a stationary member having a cross-section in the shape of a sickle and filling out the space within the big gear wheel not occupied by the small gear wheel. In gear pumps of the latter type, according to the invention, the stationary member and one of the gear wheels are preferably axially fixed in relation to one of the portions of the pump housing, and the other gear wheel is axially fixed relative to the other portion of the pump housing. Such an arrangement provides for a move ment of the gear wheels relative to each other when the portions of the pump housing are moved relative to each other; and according to a further development of the invention, the gear pump is provided with means for restricting the relative movement of the portions of the pump housing, whereby the teeth of the gear wheels remain intermeshing. In this way, both gear wheels can be kept rotating during a cleaning operation and can thus be cleaned efficiently, even when only one of the gear wheels is connected to a driving shaft, as is usually the case. According to a preferred embodiment of the invention, the gear wheel which is not driven is rotatably supported and axially fixed to a journal which is rigidly connected to the portion of the pump housing supporting said stationary member.  
  The invention will be described more in detail below, reference being made to the accompanying drawing.  
 In the drawing,  
  FIGS. 1 and 2 are longitudinal, sectional views of a gear pump in accordance with the invention, and  
  FIG. 3 is a cross-section taken along line llllll in FIG. 1.  
  The gear pump shown in the drawing has a pump housing comprising a body 1, a cylindrical member 2 connected to the body, and a wall 3 axially slidable within the cylindrical member. In FIG. 1, the slidable wall 3 engages the body I along a step 4 and together with the body defines a pump chamber 5. Sealing rings 6 are provided between the slidable wall 3 and the cylindrical member 2 of the pump housing. In the pump chamber 5, which has an inlet 7 and an outlet 8, are two rotatable gear wheels, a big wheel 9 and a small wheel 10. The big gear wheel 9 has the shape of a toothed rim having radially inwardly directed teeth 11, the spaces between the teeth also opening radially outwards. The small gear wheel 10, which is disposed within the big gear wheel 9, has the form of an ordinary gear wheel, the teeth 12 of which mesh with the inwardly directed teeth of the big gear wheel 9 along a portion of its periphery. The small gear wheel is thus eccentrically oriented with relation to the big gear wheel. In the space within the big gear wheel 9 not occupied by the small gear wheel 10, there is disposed a stationary member 13 having a cross-section in the form of a sickle. This member 13 is formed by a protrusion of the slidable wall 3, said wall also having a journal 14 on which the small gear wheel 10 is rotatably supported. The small gear wheel 10 is axially fixed relative to said journal 14 by means of a bolt 15.  
  The big gear wheel 9 is supported by a shaft 16 which extends out of the pump housing and is connected to a drive means (not shown). A sealing ring 17 is provided between the shaft and the pump housing. The big gear wheel 9 has a number of generally axially extending passages in the form of circumferentially spaced, inclined borings 90, one of which is shown in FIGS. 1 and 2, and another passage in the form of a recess la is provided in the pump housing, as shown in FIGS. 1-3. The function of these passages is to enable the space between the big gear wheel 9 and the adjacent end wall of the pump chamber to be cleaned efficiently, as will be described later.  
  During the operation of the gear pump, a fluid flows from the inlet 7 into the spaces between the teeth of the big gear wheel 9 and the small gear wheel 10 when these spaces are passing the inlet. In order to facilitate the flowing of the fluid into the spaces between the teeth, the slidable wall 3 has a recess 18 in front ofthe inlet 7, as can be seen in FIG. 1. On both sides of (i.e., radially inside and outside) the stationary member 13, the fluid is then transported by the gear wheels to the area in front of the outlet 8 where it is pressed out of the spaces between the teeth and further through the outlet 8, owing to the fact that the teeth of the two gear wheels intermesh again in this area. To facilitate the passing of the fluid out of the pump housing, the slid able wall 3 has a recess (not shown) even at the outlet 8. The big gear wheel 9 seals against the portion 1 of the pump housing circumferentially of its non-toothed portion, and the small gear wheel 10 seals against the slidable wall 3.  
  At the end of the cylindrical portion 2 of the pump housing, there is an end wall 19. A number of bolts 20 extend through this end wall and further throughout the entire pump housing, said bolts holding together the different portions of the pump housing. Within the cylindrical portion 2 of the pump housing, there is a partition wall 21 which, together with the slidable wall 3. defines a chamber 22 in the cylindrical portion 2 of the pump housing. A spindle 23 connected to the slidable wall 3 extends through the fixed partition wall 2], said spindle supporting, on the opposite side of the fixed partition wall, a second slidable wall 24 which is slidable in the cylindrical portion 2 of the pump housing. The wall 24 is attached to the spindle 23 by means of a nut 25. Sealing rings 26 and 27 are provided between the slidable wall 24 and the cylindrical portion 2 ofthe pump housing. and also between the spindle 23 and the fixed partition wall 21, whereby a sealed chamber 28 is formed between the slidable wall 24 and the fixed partition wall 21. The two sealed chambers 22 and 28 thus formed in the cylindrical portion 2 of the pump housing are adapted to be connected alternately to a pressure source (not shown), whereby the spindle 23 with the slidable walls 3 and 24 can be adjusted to the desired end position. Connection means to the pressure source are shown at 29 and 30. A guide bar 31 having a square cross section extends from said second slidable wall 24 and out through the end wall 19 of the pump housing.  
  As can be seen in FIG. 2, the rightward movement of the slidable walls 3 and 24 is restricted by the nut and the end wall 19 of the cylindrical portion of the pump housing. The portions incorporated in the gear pump have such dimensions that the small gear wheel 10, which moves axially with the slidable wall 3 of the pump housing, will not be slid out of engagement with the big gear wheel 9 when the wall 3 of the pump housing is moved to its extreme right-hand position. The  
 gear wheels can thus be kept rotating irrespective of the position of the slidable walls 3 and 24.  
  When the different portions of the pump housing have taken their positions as shown in FIG. 2, a large amount of liquid (for example, cleaning solution) can flow through the pump from the inlet 7 to the outlet 8 without being obstructed. The liquid passes from the inlet 7 radially inward through the gaps between the teeth of the big gear wheel 9 and then radially outward through said gaps in front of the outlet 8. Liquid is also caused to flow through the openings 9a of the big gear wheel 9, in a leftward direction in FIG. 2, into the space between the big gear wheel 9 and the left end wall of the pump chamber and is discharged therefrom through the recess 10 in the pump housing, whereby this space is cleaned also. The flow of the liquid through these passages is ensured by the centrifugal force acting on the liquid in the inclined openings during the rotation of the big gear wheel 9.  
 l claim:  
  1. A gear pump comprising a housing having walls forming a pump chamber, said chamber having an inlet and an outlet, first and second gear wheels rotatable about parallel axes within said chamber, said gear wheels having intermeshing elements and being adapted during normal operation of the pump to sealingly engage adjacent walls of the pump chamber, one of said first gear wheel and a first said wall being mounted for axial displacement relative to the other of said first wheel and first wall, whereby the sealing engagement between said first wheel and first wall is interrupted, and a device operable independently of an above-normal pressure in the pump chamber to effect said displacement and thereby establish a free passage through the pump chamber, said passage permitting a generally free flow of fluid through the pump chamber between its inlet and outlet.  
  2. The gear pump of claim 1, in which said device includes means located outside the pump housing and connected to said first gear wheel, said means being op erable to positively displace the first gear wheel in opposite directions relative to the second gear wheel.  
  3. The gear pump of claim 1, in which said first wall is movable relative to a second of said walls in the axial direction of the gear wheels, said first and second walls being sealingly interconnected to enable the pump chamber to expand by movement of said first wall away from said second wall.  
  4. The gear pump of claim 3, in which one of said first and second walls is included in a portion of the housing which surrounds the other of said first and second walls.  
  5. The gear pump of claim 3, in which each of said gear wheels is axially fixed relative to one of said first and second walls.  
  6. The gear pump of claim 3, comprising also means for restricting relative movement of said first and second walls to maintain intermeshing of the gear wheels.