Patent Publication Number: US-6210138-B1

Title: Rotary pump apparatus and method

Description:
TECHNICAL FIELD 
     This invention relates to rotary pump apparatus incorporating structure for reducing cavitation during pump operation and reducing pump damage caused by cavitation. The invention also encompasses a method. 
     BACKGROUND OF THE INVENTION 
     Rotary pumps are well known structures employed to pump fluids from one location to another. Rotary gear pumps conventionally employ two gears having meshing teeth disposed in a rotary pump housing to deliver fluid entering the housing interior from an inlet opening to an outlet opening. One of the toothed gears is a drive gear rotated by a motor or other suitable means while the other gear conventionally is a driven gear driven by and rotating in response to rotation of the drive gear. 
     It is not at all unusual for cavitation pitting damage to occur in rotary pumps. Typically such damage will be in the form of pitting occurring within the interior of the pump housing. Pump life can be drastically reduced and considerable time and expense can be involved when repairing or replacing pumps having cavitation pitting damage. 
     DISCLOSURE OF INVENTION 
     The present invention is directed to a rotary pump apparatus and to a method for reducing cavitation damage. 
     The rotary pump apparatus of the present invention includes a pump housing defining a housing interior, a fluid inlet opening in communication with the interior and a fluid outlet opening in communication with the interior and spaced from the fluid inlet opening. 
     A drive gear having drive gear teeth is rotatably mounted relative to the pump housing and located within the housing interior. 
     A driven gear having gear teeth is rotatably mounted relative to the pump housing and located within the housing interior. The gear teeth of the drive gear mesh with the gear teeth of the driven gear and define therewith a space located between the meshing drive gear teeth and the driven gear teeth varying in volume during rotation of the drive and driven gears. 
     A fluid-flow passageway extends between the inlet fluid opening and the space for introducing fluid into the space from the fluid inlet opening during increase in volume of the space during rotation of the drive and driven gears to relieve negative fluid pressure within the space during the increase in volume. 
     The invention further encompasses a method of reducing cavitation in a rotary pump, the pump including a pump housing forming a housing interior and a pair of rotating toothed gears forming a gear mesh located in the housing with the teeth of the gears engaged in the mesh forming a volumetrically variable space during gear rotation. 
     The method includes the step of establishing a fluid-flow passageway extending to the gear mesh. 
     Fluid is introduced into the fluid-flow passageway and the method further includes the step of flowing the introduced fluid through the fluid-flow passageway. 
     The fluid flowing through the fluid-flow passageway is directed into the space during rotation of the gears to relieve negative fluid pressure in the space caused by the rotation. 
     In the illustrated preferred embodiment, a fluid inlet opening is formed in the pump housing and the fluid-flow passageway is established between the fluid inlet opening and the gear mesh, the fluid flowing into the fluid-flow passageway from the fluid inlet opening. 
     Other features, advantages, and objects of the present invention will become apparent with reference to the following description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of rotary pump apparatus constructed in accordance with the teachings of the present invention; 
     FIG. 2 is an elevational view of the apparatus illustrating the fluid inlet and outlet openings or ports thereof, with interior structural features of the apparatus shown by dash lines; 
     FIG. 3 is a perspective view of a cap incorporated in the pump housing and illustrating an interior wall thereof defining fluid inlet and outlet openings and a fluid-flow passageway in the form of a channel formed in the cap; 
     FIG. 4 is an elevational view of the cap as seen from the interior of the housing; 
     FIG. 5 is an exploded, perspective view illustrating structural components of the rotary pump apparatus prior to assembly thereof; 
     FIG. 6 is an enlarged, partial cross-sectional view taken along the line  6 — 6  of FIG. 2; 
     FIG. 7 is an enlarged, cross-sectional view taken along the line  7 — 7  of FIG. 2; and 
     FIGS. 8-10 are somewhat diagrammatic enlarged views of gear mesh teeth of the rotary pump apparatus during sequential stages of operation thereof and their relationship to a fluid-flow passageway formed in the pump housing and extending to the mesh, the location of the fluid-flow passageway being depicted by phantom lines. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Referring now to the drawings, rotary pump apparatus constructed in accordance with the teachings of the present invention is illustrated. The apparatus includes a pump housing  10  having a housing interior. In the arrangement illustrated, the pump housing includes a cap  14 , a housing body  16  and a housing member  18  having a cylindrical outer surface secured between the cap  14  and housing body  16  by any suitable expedient such as bolts  20  threadedly engaged with housing body  16 . 
     Cap  14  of the pump housing has a fluid inlet opening  22  and a fluid outlet opening  24  formed therein at spaced locations in a conventional manner. The fluid inlet opening is of course connected to a source (not shown) of fluid to be pumped and fluid outlet opening  24  communicates with a downstream fluid flow path (not shown). 
     Formed in the inner wall of the cap  14  are two recesses  26  which receive bushings  28  therein. A circular groove  30  receives an O-ring seal  32  to provide a fluid-tight seal between cap  14  and housing member  18  when the apparatus is secured together. 
     Positioned in housing member  18  are a drive gear  40  and a driven gear  42  having gear teeth  44 ,  46 , respectively, disposed thereabout. Stub shafts  48  project from the gears and are rotatably disposed in bushings  28 . 
     The gears  40 ,  42  are disposed in a cavity  50  formed in housing member  18 , the gears closely conforming to the shape of the cavity to deliver fluid from fluid inlet opening  22  to fluid outlet opening  24  in the spaces between the gear teeth and the housing member  18  in a well known manner. 
     An elongated shaft  52  projects from drive gear  40  through a hole  54  formed in housing body  16 , a bushing  56  being employed to rotatably support the shaft  52 . Any suitable means such as the output shaft of a motor (not shown) may be employed to rotate shaft  52  and drive gear  40 . The intermeshing of the teeth of the drive gear and the driven gear cause driven gear  42  to rotate with the drive gear. A stub shaft  58  projecting from driven gear  42  is rotatably positioned in a bushing  60  residing in a recess  62  of the housing body  16 . An O-ring seal  64  maintains the housing body  16  and housing member  18  in fluid-tight relationship. 
     The illustrated pump housing, drive and driven gears and related structure just described are of a conventional nature and such construction is merely representative of rotary pump structures to which the teachings of the present invention are applicable. 
     FIGS. 8 through 10 illustrate rotation of drive gear  40  and driven gear  42  during pump operation when pumping fluid from fluid inlet opening  22  to fluid outlet opening  24 . The gears rotate in the directions shown by the arrows in these figures. In these figures, two adjacent teeth  46  of driven gear  42  and one tooth  44  of drive gear  40  are designated or marked by dots and one can readily follow the relative movement of the these marked teeth for an illustration of the problems that can occur in conventional rotary pumps that produce pitting or other cavitation caused damage. 
     It will be noted that in FIG. 8 a tooth  44  is centered between two teeth  46 . Fluid is trapped in the space formed by the two marked teeth  46  and the marked tooth  44 . This space is designated by reference numeral  72 . Further rotation of the gears as shown in FIG. 9 will cause the space to increase volumetrically to a significant degree. That is, an expanding volume is created at the roots of the gear teeth in the mesh. This expansion in volume can cause the fluid pressure in the space to drop below fluid vapor pressure and vapor cavities to be formed in the space. Once the gear mesh opens to the suction fluid these cavities will implode if the suction pressure is high enough. This action results in pitting of the pump components over a period of time. FIG. 10 illustrates the fluid entering the space from outside the mesh. However, in a conventional rotary pump the volume of the space expands faster than the fluid in the pump interior is capable of filling the space. 
     The above-described problem has been solved by the present invention and the solution is accomplished simply and inexpensively. 
     More specifically, a fluid-flow passageway in the form of a channel  70  is formed in the pump housing, the channel extending between inlet fluid opening  22  and the volumetrically varying space  72  formed by three meshing teeth of the drive gear and driven gear. This arrangement provides the desired amount of “make-up” fluid in the space as it expands and prevents the formation of vapor cavities in the fluid during expansion of the space. That is, the fluid from channel  70  prevents the pressure in the space from dropping below the vapor pressure of the fluid. 
     The fluid-flow passageway or channel  70  has a tapered, tear-shaped cross-section diminishing in size in the direction of the space  72  and directs a portion of the fluid passing through the fluid inlet opening to the space. The fluid-flow passageway has a distal end adjacent to the space and the fluid-flow passageway is partially covered by the meshing drive gear teeth and the driven gear teeth. The interior or end wall of the cap  14  is otherwise in substantially fluid-tight relationship with the drive gear and the driven gear, as is the inner wall of housing body  16 . 
     The distal end of the fluid-flow passageway is located at the gear mesh and equi-distant from the axis of rotation of the rotating toothed gears. Thus, the fluid-flow passageway can provide “make-up” fluid to all spaces serially formed at the mesh during rotation of the gears.