Abstract:
A gear pump having double-helical gears with bearing assembly seals and gear end seals which provided double seal interfaces between the pump cavity and bearing cups having disposed therein bearing assemblies for supporting pump shafts for rotation. The double seal interfaces preclude pumped fluid, particularly contaminated fluid including entrained abrasives from making contact with the bearing assemblies. An adjustable packing seal mechanism, a gear gap adjustment mechanism, a fluid pressure relief system, and pump heat exchanger features are also disclosed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to pumps used to pump liquids entrained with abrasives, and more particularly, relating to a gear pump including double-helical gears of an construction which reduces end plate wear, reduces the tendency for contaminated fluids fouling pump shaft bearing assemblies, permits packing seal adjustment to compensate for seal wear, and permits the adjustment of gear gap between meshing gear teeth. 
       BACKGROUND OF THE INVENTION 
       [0002]    Pumping liquids and fluids, such as oils and distillates produced from oil wells, presents a problem as these fluids frequently contain entrained contaminating materials such as sand, grit and the like. The pumping of such fluids results in the entrained abrasive materials coming into contact with the pump elements, and in particular, the pump surface elements as well as the pump shaft bearings and seals. Consequently, pumps in service for pumping such liquids require frequent maintenance and repair as a result of premature wear and failure after a relatively short period of use. Pumps employing meshing gears are often used to pump such fluids. Such gear pumps typically include single-helical gears that in operation, as a result of contact between the meshed gear teeth, create axial thrust forces along the pump shafts, which causes an increase in end plate wear. 
         [0003]    To address these problems, pumps include modular designs to increase the serviceability of the pump and reduce overall pump downtime, include wear plates to take the axial thrust forces along the pump shafts to reduce end plate wear, and include bearing assemblies and seal arrangements that operate to reduce the tendency of contaminated fluid contact with the bearing assemblies. 
         [0004]    Another problem encountered is leaking of fluid externally of the pump due to a worn dynamic packing seal that is used to provide a seal between the protruding end of the pump driving shaft and the pump housing or end plate. Heretofore, servicing and replacement of the packing seal required the pump to be shutdown. 
         [0005]    Another problem encountered is the formation of area of high pressurized fluid at the end of a pump shaft created during the pump operation. The pressurized fluid creates an axially loading on the pump shaft causing the pump shaft to be urged towards the opposite end resulting in an increase of pump component wear. 
         [0006]    Accordingly, there is a need for a pump design used to pump fluids contaminated with abrasives that has an increased service life and an improved serviceability and that overcomes the limitations associated with conventional pump designs heretofore. 
       SUMMARY OF THE INVENTION 
       [0007]    In general, in one aspect, a gear pump is provided including a pump housing having opposite ends. A gear is disposed within the pump housing and includes opposed and outwardly facing first and second ends. The first end having a first gear end seal mount, and the second end having a second gear end seal mount. First and second end plates are sealingly joined to the opposite ends of the pump housing. The first end plate has a first shaft passage to receive a pump shaft therethrough and a first seal disc mount on an inner side of the first end plate coaxial with the first shaft passage. The second end plate has a second shaft passage to receive a pump shaft therethrough and a second seal disc mount on an inner side of the second end plate coaxial with the second shaft passage. A first seal disc is mounted to the first seal disc mount. A second seal disc is mounted to the second seal disc mount. A pump shaft having a first shaft end extends through the first shaft passage and the first seal disc, and a second shaft end extends through the second shaft passage and the second seal disc. The gear is fixedly joined to the pump shaft for rotation therewith. A first gear end seal is mounted to the first gear end seal mount and forms a sealing contact between an inner facing side the first seal disc and the first outwardly facing end. A second gear end seal is mounted to the second gear end seal mount and forms a sealing contact between an inner facing the second seal disc and the second outwardly facing end. 
         [0008]    In general, in another aspect, a gear pump includes a first fluid flow passage between the first shaft end and a first discharge/suction port, and a second fluid flow passage between the first shaft end and a second discharge/suction port. Fluid at the first shaft end flows through either of the first or the second fluid passage upon the fluid reaching a pressure above a threshold pressure to vent the fluid at the first shaft end to either of the first or the second discharge/suction ports, respectively. 
         [0009]    In general, in another aspect, a gear pump includes a seal neck including a body having opposed first and second ends and a seal neck shaft passage extending between the first and second ends. The seal neck mounted to the end plate and the pump shaft extending through the seal neck passage and protruding beyond the second end of the seal neck. First and second bushings disposed in the seal neck shaft passage and supporting the pump shaft for rotation. A packing seal disposed within the seal neck shaft passage about the pump shaft and interdisposed between the first and the second bushings. A packing nut including a bore is threadably attached to the second end of the body of the seal neck. The pump shaft extending through the bore of the packing nut, wherein threading the packing nut on the second end compresses the packing seal between the first and the second bushings. A pair of check balls, each disposed in a hole extending through a body of the packing nut. A collar attached to packing nut about the body thereof. The collar captivity retaining the pair of check balls in the holes and rotatable about the body between first and second positions. The collar including a pair of cavities on an interior surface thereof. The seal neck including a plurality of flat lands circumferentially spaced on an exterior surface thereof. The collar is rotated into the first position the cavities are registered with the holes through the packing nut body and the check balls are partially received within the cavities permitting the check balls to float across the flat lands as the packing nut is threaded, and wherein the collar is rotated into the second position the check balls are restrained from floating across the flat lands. 
         [0010]    In general, in another aspect, a gear pump includes double-helical gears shrunk fit to respective driving and idler pump shafts. 
         [0011]    In general, in another aspect, a gear pump includes a plug member threadably received by a plug bore through the first end plate along the axis of the pump shaft. The first shaft end of the pump shaft including an axial bore. A ball is disposed between the first shaft end and a cup of an inward end of the plug member. 
         [0012]    There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood and in order that the present contribution to the art may be better appreciated. 
         [0013]    Numerous objects, features and advantages of the present invention will be readily apparent to those of ordinary skill in the art upon a reading of the following detailed description of presently preferred, but nonetheless illustrative, embodiments of the present invention when taken in conjunction with the accompanying drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of descriptions and should not be regarded as limiting. 
         [0014]    As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
         [0015]    For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated preferred embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The accompanying drawings, which are included to provide further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate preferred embodiments of the invention and together with the description serve to explain the principles of the invention, in which: 
           [0017]      FIG. 1  is perspective view of a gear pump constructed in accordance with the principles of the present invention show assembled; 
           [0018]      FIG. 2  is a top view of the gear pump schematically illustrating a pressure relieving system; 
           [0019]      FIG. 3  is a cross sectional view of the gear pump taken along line  3 - 3  in  FIG. 2 ; 
           [0020]      FIG. 4  is an exploded view of the gear schematically illustrating components of the gear pump; 
           [0021]      FIGS. 5A-5C  schematically illustrate embodiments of floating dynamic seals receivable in gear end seal mounts; 
           [0022]      FIG. 6  is an enlarged schematic view of the gear pump seal neck; 
           [0023]      FIG. 7  is an enlarged schematic, cross-sectional view of the gear pump seal neck taken along line  7 - 7  in  FIG. 6 , and illustrating an adjustable pump shaft packing seal; 
           [0024]      FIG. 8  is an enlarged schematic, cross-sectional view of the seal neck taken along line  8 - 8  in  FIG. 6 , and illustrating a lock assembly of the packing nut; 
           [0025]      FIG. 9  is an exploded, schematic perspective view of the seal neck, packing nut and packing nut lock assembly; 
           [0026]      FIG. 10  is a schematic view of a fluid pressure relief system of the gear pump; 
           [0027]      FIG. 11  is perspective view of a modified end plate and schematically illustrating the fluid pressure relieving system; 
           [0028]      FIG. 12  is an enlarge, partial cross-sectional view of a gear gap adjustment mechanism of the gear pump; 
           [0029]      FIG. 13  is an enlarged side elevation view of a threaded plug of the gear gap adjustment mechanism; 
           [0030]      FIG. 14  is an enlarged end view of the threaded plug; 
           [0031]      FIG. 15  is an enlarged cross-sectional view of the threaded plug taken along line  15 - 15  in  FIG. 14 ; 
           [0032]      FIG. 16  is a schematic cross-sectional view of the gear pump including heat exchange features; and 
           [0033]      FIG. 17  is a schematic view of a fluid medium heat exchange feature. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    Schematically illustrated In  FIGS. 1-4  is a specially designed gear pump  10  for pumping liquids and fluids, such as oils and distillates containing entrained contaminates such as sand, girt and the like. The gear pump  10  is of the external gear pump type having a driving gear and a driven gear which are disposed within a pump cavity of the gear pump which mesh with each other. The two gears rotate to move a fluid caught in their tooth spaces from a suction side toward a discharge side, thereby performing a pumping action. 
         [0035]    Gear pump  10  includes a pump housing  12  having opposite open ends  14 ,  15  and a sidewall  16  extending therebetween. Sidewall  16  forms a pump cavity  18  and includes opposing suction/discharge ports  20  and  22  extending through the sidewall and into the pump cavity. A pair of end plates  24 ,  26  are sealingly attached to ends  14 ,  15 , respectively, and seal the pump cavity  18 . Each end plate  24 ,  26  includes a plurality of peripherally disposed fastener mounts such as bolt holes  28  which are used to fasten the end plate to the pump housing  12  by bolts  30 . 
         [0036]    A pair of meshing gears  32  and  34  are disposed within the pump cavity  18  and extend between end plates  24 ,  26 . Gear  32  is supported by pump shaft  36  which is the pump driving shaft. Gear  34  is supported by pump shaft  38  which is the pump idler shaft. The gears  32 ,  34  are fixedly secured to driving shaft  36  and idler shaft  38 , respectively, for conjoined rotation therewith. To eliminate undesirable play between the gear and shaft, and undesirable meshing between gears  32 ,  34  during high torque startup, the conventional key and keyway coupling between shaft and gear is replaced by shrink fitting gears  32 ,  34  to the driving shaft  36  and idler shaft  38 , respectively. In this manner, gear  32  and driving shaft  36  become a unitary assembly, and gear  34  and idler shaft  38  become a unitary assembly. The unitary gear/shaft assemblies eliminates vibration between the gear and shaft which serves to reduce pump noise, increase life expectancy of the gears, and to reduce cavity phenomena. 
         [0037]    Gears  32 ,  34  are double-helical gears. The use of double-helical gears eliminates the problem of axial thrust on the pump shafts  36 ,  38  that is presented by “single” helical gears by having two sets of teeth that are set in a V shape. Each gear in a double helical gear can be thought of as two standard mirror image helical gears stacked. This cancels out the thrust since each half of the gear thrusts in the opposite direction. In this manner the use of wear plates employed to prevent end plate wear in gear pumps is eliminated, and thus reduces the cost of manufacture and maintenance of the gear pump. 
         [0038]    Still referring to  FIGS. 1-4 , end plates  24 ,  26  are of a similar construction and each include an inward facing side  40  and an opposed outward facing side  42 . In some aspects, end plates  24  and  26  are interchangeable, and can be mounted on either ends  14 ,  15  of pump housing  12 . Outward facing side  42  includes a pair of bearing cups or mounts  44 ,  46  extending outwardly therefrom. First and second shaft passages  48 ,  50  extend through end plate  24 ,  26  from the inward facing side  40  through bearing cups  44 ,  46 , respectively, to the outward facing side  42 . Bearing cup caps  52 A,  52 C are sealing attached to the outward facing side of end plate  24  and seal bearing cups  44 ,  46 , respectively. Bearing cup cap  52 D is sealing attached to the outward facing side of end plate  28  and seals bearing cup  46 . A packing neck  54  is sealing attached to the outward facing side  42  of end plate  28  and seals bearing cup  44 . Bearing cup caps  52 A,  52 B and  52 C can be fitted with grease zurks to permit greasing of the shaft bearing assemblies positioned therein. 
         [0039]    Referring to  FIGS. 3 and 4 , end plate  24  includes seal disc mounts  58 A and  58 C on the inward facing side  40  thereof and coaxial with shaft passages  48  and  50 , respectively. Likewise, end plate  26  includes seal disc mounts  58 B and  58 D on the inward facing side  40  thereof and coaxial with shaft passages  48  and  50 , respectively. Seal discs  60 A,  60 B,  60 C, and  60 D are mounted to seal disc mounts  58 A,  58 B,  58 C, and  58 D, respectively, and cover the inward facing opening of the bearing cups  44 ,  46  of each end plate  24 ,  26 . In embodiments, seal disc mounts  58 A,  58 B,  58 C, and  58 D are each a recess formed on the inward facing side  40  of end plates  24  and  26 , respectively, into which seal discs  60 A,  60 B,  60 C, and  60 D are received. Seal discs  60 A,  60 B,  60 C, and  60 D may be fastened to end plates  24  and  26 , respectively by threaded fasteners. In embodiments, seal discs  60 A,  60 B,  60 C, and  60 D are flush with the inward facing side  40  of end plates  24  and  26 , respectively. Seal discs  60 A,  60 B,  60 C, and  60 D may also be referred to as pressure washers at they each taking loading forces from gear end seals, as further described below. 
         [0040]    Still referring to  FIGS. 3 and 4 , end  62  of the driving shaft  36  extends through seal disc  64 A and into shaft passage  48  of end plate  24  and is supported for rotation by bearing assembly  64 A disposed in bearing cup  44 . Bearing assembly  64 A includes a bushing  66 A which supports end  62  for rotation and a pair of end seals  68 A and  70 A that are disposed within recesses formed in opposing ends of bushing  66 A. End seals  68 A and  70 A provide sealing contact between the driving shaft  36  and bushing  64 A. Further, end seal  68 A provides a sealing contact between the bearing cup facing side of seal disc  58 A and bushing  66 A. 
         [0041]    The opposite end  72  of driving shaft  36  extends through seal disc  64 C, shaft passage  48  of end plate  26  and through packing neck  54 . End  72  is supported for rotation by bearing assembly  64 C disposed in bearing cup  44 . Bearing assembly  64 C includes a bushing  66 C which supports end  72  for rotation and a pair of end seals  68 C and  70 C that are disposed within recesses formed in opposing ends of bushing  66 C. End seals  68 C and  70 C provide sealing contact between the driving shaft  36  and bushing  66 C. Further, end seal  68 C provides a sealing contact between the bearing cup facing side of seal disc  58 C and bushing  66 C. 
         [0042]    Likewise, end  74  of idler shaft  38  extends through seal disc  58 B and into shaft passage  50  of end plate  24 , and is supported for rotation by bearing assembly  64 B disposed in bearing cup  46 . Bearing assembly  64 B includes a bushing  66 B which supports end  74  for rotation and a pair of end seals  68 B and  70 B that are disposed within recesses formed in opposing ends of bushing  66 B. End seals  68 B and  70 B provide sealing contact between the idler shaft  38  and bushing  66 B. Further, end seal  68 B provides a sealing contact between the bearing cup facing side of seal disc  58 B and bushing  66 B 
         [0043]    The opposite end  76  of idler shaft  38  extends through seal disc  58 D and into shaft passage  50  of end plate  26 , and is supported for rotation by bearing assembly  64 D disposed in bearing cup  48 . Bearing assembly  64 D includes a bushing  66 D which supports end  76  for rotation and a pair of end seals  68 D and  70 D that are disposed within recesses formed in opposing ends of bushing  66 D. End seals  68 D and  70 D provide sealing contact between the idler shaft  38  and bushing  66 D. Further, end seal  68 D provides a sealing contact between the bearing cup facing side of seal disc  58 D and bushing  66 D. 
         [0044]    Still referring to  FIGS. 3 and 4 , gear end seal  78 A is disposed about driving shaft  36  and between the inward facing side of seal disc  58 A and end  80  of gear  32 . Gear end seal  78 A provides a sealing contact between end  80  of gear  32  and the inward facing side of seal disc  58 A. Gear end seal  78 A is mounted to gear end mount  82 A on end  80  of gear  32 . Gear end seal  78 C is disposed about driving shaft  36  and between the inward facing side of seal disc  58 C and end  84  of gear  32 . Gear end seal  78 C provides a sealing contact between end  84  of gear  32  and the inward facing side of seal disc  58 C. Gear end mounts  82 A and  82 C are recesses in ends  80  and  84 , respectively which gear end seals  78 A and  78 C are disposed. 
         [0045]    Gear end seal  78 B is disposed about idler shaft  38  and between the inward facing side of seal disc  58 C and end  86  of gear  34 . Gear end seal  78 B provides a sealing contact between end  86  of gear  34  and the inward facing side of seal disc  58 B. Gear end seal  78 B is mounted to gear end mount  82 B on end  88  of gear  34 . Gear end seal  78 D is disposed about idler shaft  38  and between the inward facing side of seal disc  58 D and end  88  of gear  34 . Gear end seal  78 D provides a sealing contact between end  88  of gear  34  and the inward facing side of seal disc  58 D. Gear end mounts  82 B and  82 D are recesses in ends  86  and  88 , respectively which gear end seals  78 B and  78 D are disposed. In embodiments, gear end seals  78 A,  78 B,  78 C and  78 D are floating seals. However, it is contemplated the floating seals could be replaced with non-floating seals and provide a sealing contact as intended. 
         [0046]    Fluids from the pump cavity  18  are kept from contact with bearing assembly  64 A by means of end seal  68 A, seal disc  58 A and gear end seal  78 A, from bearing assembly  64 B by means of end seal  68 B, seal disc  58 B and gear end seal  78 B, from bearing assembly  64 C by means of end seal  68 C, seal disc  58 C and gear end seal  78 C, and from bearing assembly  64 D by means of end seal  68 D, seal disc  58 D and gear end seal  78 D. To this end, debris entrained in the pumped fluid are prevented from contact with bearing assemblies  64 A,  64 B,  64 C and  64 D, and thus extending the service life thereof. 
         [0047]    With reference to  FIGS. 5A ,  5 B and  5 C, a plurality of embodiments of gear end seals  78 A- 78 D are shown. In  FIG. 5A , there is shown an elastic frontal labyrinth seal. In  FIG. 5B , there is shown a frontal labyrinth seal with O-ring as elastic element. In  FIG. 5C , there is shown a frontal labyrinth seal with wave spring as elastic element. 
         [0048]    Schematically depicted in  FIGS. 6-9 , is gear pump  10  having an adjustable driving shaft packing seal assembly  100 . Packing seals are conventional used to prevent fluid that is being pumped from leaking through the exposed interface between the protruding pump shaft and the pump housing. As the packing seal becomes worn, the seal begins to fail and leak. Heretofore, the only solution to a worn, leaking packing seal is to shutdown the pump to allow the disassembly and the replacement of the worn packing seal components. The assembly  100 , embodied herein, permits an operator to adjust the packing seal as it becomes worn in order to extend the service life of the packing seal without requiring the pump to be shutdown. 
         [0049]    Seal neck  54  comprises a body  102  having opposed ends  104  and  106 , and a longitudinal shaft passage  108  extending through ends  104  and  106 . End  104  is adapted to be mounted to bearing cup  44  with driving shaft  36  extending through shaft passage  108  and beyond end  106  with end  72  protruding externally to permit operable coupling of the driving shaft to a source of rotational power, such as an engine or motor. A pair of bushings  110  and  112  are disposed within shaft passage  108  about driving shaft  36  and provide rotational support to the driving shaft. A packing seal  114 , such as a Teflon rope, is interdisposed between bushings  110  and  112  about drive shaft  36 , and provides a seal interface between driving shaft  36  and shaft passage  108 . A packing nut  110  is threaded onto end  106  of seal neck  54  with driving shaft  36  extending through shaft bore  116 . 
         [0050]    Bushing  110  is disposed in shaft passage  102  with end  118  thereof abutting against shoulder surface  120  of shaft passage  102  and with the opposite end  122  engaged with end  124  the packing seal  114 . End  124  may be inwardly chamfered to provide a seat into which end  124  of the packing seal is received. Busing  112  is disposed in shaft passage  102  with end  126  thereof extending beyond end  106  of seal neck  54  and engaged with surface  128  of the pack nut  110 . The opposite end  130  of bushing  112  is engaged with end  132  of packing seal  114 . End  130  may be inwardly chamfered to provide a seat into which end  132  of the packing seal  114  is received. Threading packing nut  110  onto seal neck  54  causes bushings  110  and  112  to compress packing seal  114  between ends  118  and  130  of bushings  110  and  112 , respectively, and creates a sealing contact between driving shaft  36  and shaft passage  108 . 
         [0051]    The assembly  100  further includes a packing nut lock  140  that operates to either preclude the turning of packing nut  110  when moved into one position or to permit the turning of packing nut when moved into another position. As best seen in  FIGS. 7 and 8 , the packing nut lock  140  includes a collar  142  fitted about packing nut body  144 . Collar  142  is secured to body  144  for axial rotation about packing nut body by a pair of pins  146  and  148  that are inserted through holes  150  and  152 , respectively, of collar  142  and at least partially into slots  154  and  156 , respectively, of packing nut body  144 , as best seen in  FIG. 8 . In this manner, the collar  142  is limited to a few degrees of rotation about packing nut body  144  between a first position and a second position. The assembly of collar  142  with packing nut body  144  captivity retains a pair of check balls  158  and  160  in holes  162  and  164 , respectively, of the packing nut body  144  by the inner surface  146  of the collar. A plurality of flat lands  170  are circumferentially located on the exterior surface of the seal neck  54 . 
         [0052]    When collar  142  is rotated into the first or ON position, as shown in  FIG. 8 , cavities  166  and  168 , formed on the interior surface of collar  142 , are registered with holes  162  and  164 . This registration permits check ball  158  to be partially received by cavity  166  and check ball  160  to be partially received by cavity  168 . In this manner, packing nut  110  is permitted to be rotated about seal neck  54  with check balls  158  and  160  floating over lands  170 . When collar  142  is rotated into the second or OFF position, cavities  166  and  168  are moved out of registration with holes  162  and  164 , and the inner surface  146  presses check balls  158  and  160  against a flat land  170 , as shown in  FIG. 8  in dashed line. In this manner, packing nut  110  is precluded from rotating about seal neck  54 , and therefore, is locked. 
         [0053]    In operation, as packing seal  118  becomes worn and leaks, an operator may further compress the packing seal  118  to tighten the seal between the shaft passage  108  and the driving shaft  36  to preclude the leaking without shutting down the operation of the pump. The packing seal  118  is further compressed by rotating collar  142  into the ON position and then rotating the packing nut  110  further onto the seal neck  54 . Once fluid stops leaking, collar  142  is rotated into the OFF position, thereby locking the threaded position of the packing nut  110  on the seal neck. 
         [0054]    Schematically depicted in  FIGS. 2  an  10 , is gear pump  10  having pressure relief system to vent fluid pressure that may occur at end  62  of driving shaft  36  to prevent axially forces along driving shaft and avoiding end plate wear. The pressure relief system includes first and second fluid passages  200  and  202 , each in fluid communication with fluid located at end  62  of the driving shaft  36 . The first passage  200  is further in fluid communication with suction/discharge port  20 , and the second passage  202  is further in fluid communication with suction/discharge port  22 . A check valve  206  and needle valve  208  are positioned across the first passage  200  and a check valve  210  and needle valve  212  are positioned across the second passage  202 . Check valves  206  and  210  operate to permit fluid to follow through passages  200  and  202 , respectively, only in the direction towards suction/discharge ports  20  and  22 . Needle valves  208  and  212  are each adjust to permit fluid flow through passages  200  and  202 , respectively, when fluid at end  62  of the driving shaft  36  is at a threshold pressure. In  FIG. 11 , end plate  24  is schematically depicted including ports  214  and  216  for connection with fluid passages  200  and  202  with suction/discharge ports  20  and  22 , respectively. Needle valves  208  and  212  are optional. Additionally, while the pressure relief system is illustrated and described with reference only to end  62  of driving shaft  36 , the pressure relief system can be employed to release pressure at the ends of any of the pump shafts. 
         [0055]    Schematically depicted in  FIGS. 12-15 , is gear pump  10  having a gear gap control mechanism  300  to adjust the meshing of gears  32  and  34  by axially displacing driving shaft  36 . In this embodiment, bearing cup cap  52 A is replaced by bearing cup cap  52 A′ and end  62  of driving shaft  36  has been milled to include axial bore  302 . Mechanism  300  further includes a plug member  304  threadably received by bore  306  that extends through end plate  24  along longitudinal axis  307  of driving shaft  36 . Inward end  308  of plug  304  includes bore  310  into which is disposed is cup member  312 . Ball  314  is interdisposed between end  62  of the driving shaft  36  and cup member  312 , and is partially seated within cup member  312  and axial bore  302 . Ball  314  provides a dynamic bearing interface between cup member  312  and end  62  of the driving shaft  36 . Threading plug  304  into bore  306  causes ball  314  to urge against end  62  of the driving shaft  36 . Further threading of plug  304  into bore  306  results in a longitudinal displacement of driving shaft  36  along axis  306 , and thus moves the longitudinal position of gear  32  relative to the longitudinal position of gear  34 . The threaded position of plug  304  can be adjusted to control relative longitudinal positions of gears  32  and  34 , and thus the gap between the gear teeth. The threaded position of plug  304  can be locked in place by a screw or threaded pin  316  threadably received within bore  318  that extends normal to bore  306 . Threading pin  316  into bore  318  caused end  320  of the pin to be received by one of a plurality of circumferentially spaced and longitudinally extending grooves  322  on the exterior of plug barrel  324 , and thus locking plug  304  from rotation within bore  306 . An O-ring seal  326  can provide a sealing interface between bore  306  and plug  304 . Additionally, while the gap control is illustrated and described with reference only to end  62  of driving shaft  36 , the gap control can be employed to at the ends of any of the pump shafts. 
         [0056]    Schematically depicted in  FIGS. 16 and 17 , is gear pump  10  having one or more heat exchange features to either cool the gear pump in hot climates or heat the gear pump in cold climates. In one aspect, a heat exchanger body  402  is mounted to the exterior of the pump housing  12 , for example by welding. One or more electric heating elements  404  are disposed within body  402  that are operably connected to a source of electrical power (not shown) by leads  405 . When operating, electric heating elements  404  output radiant heat that is transmitted into the pump casing  12  and heating the components of the pump  10  to prevent lockup due operating in cold climates. In another aspect, a heat exchanger body  406  is mounted to the exterior of the pump housing  12 , for example by welding. Body  406  include an internal serpentine fluid flow passage  407  extending between inlet and out let ports  408  and  410 . Ports  408  and  410  are fitted with couplings  412  that permit the flow passage  407  to be fluidically connected to an engine cooling system (not shown) to receive the flow of antifreeze or other heat exchanging fluid medium  414  from the engine cooling system. The flow of fluid through flow passage  407  heats or cools the pump housing  12  and thus the pump components to prevent lockup due to freezing weather or from over heating. 
         [0057]    A number of embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.