Abstract:
The subject matter of this specification can be embodied in, among other things, a fluid pump that includes a housing with a cam block. The pump also includes a collection of vanes, each having a shank having a leading edge and a trailing edge, and a head having a curved outer side. The pump also includes a rotor having a collection of slots, each slot having substantially parallel leading and trailing edges spaced to accommodate the shank of one of the vanes, wherein each vane contacts the cam block at a contact point on the head controlled by the rotor slot position and the head outer curved surface, the contact point being located relative to the shank edge when the vane is radially aligned with the major and minor radii, and located rotationally to create a radial force between the head curved surface and the cam block.

Description:
TECHNICAL FIELD 
       [0001]    This instant specification relates to dual-lobe vane style positive displacement high pressure (HP) pumps. 
       BACKGROUND 
       [0002]    Dual lobe vane style positive displacement high pressure (HP) pumps, such as the example pump  100  shown in  FIG. 1 , utilize a collection of vanes  102  having a crown radius with a center on the central plane of the vane. Each of a collection of vanes  102  is contained within a corresponding rotor slot  104  centered about a radial line which passes through the center of a rotor  106 , e.g., the center of rotation. The rotor  106  and vanes  102  are then contained inside a cam  108  and axially between two port plates (not shown). The rotor  106 , vanes  102 , cam  108 , and port plates are sandwiched between two backing plates (not shown) which contain porting passages to interface with a housing (not shown) allowing the separation of an inlet flow from an outlet flow. The rotor  106  is supported on a shaft  112  which in turn is supported by bearings (not shown) typically mounted in the two backing plates, although other bearing arrangements are possible. The port plates and the cam  108  are axially sandwiched by the backing covers which are axially retained either by fasteners, e.g., bolts, pressure loading, or both. A collection of pumping chambers  114  are formed by two adjacent vanes  102 , a cam inside surface  110 , the rotor  106  outside radius and the port plate axial surfaces. The pumping action is created by the change in the length of the radius on the inside surface  110  of the cam  108  between a smaller radius  120 , e.g., minor radius, and a larger radius  122 , e.g., major radius. 
         [0003]    The rotor  106  is rotated by the shaft  112  and urges the vanes  102  to rotate relative to the cam  108 . The vane  102  is urged into contact with the cam  108  inner surface at the peak of the crown radius to form a sliding seal with the cam inside surface  110  completing the pumping chambers  114 . The rotor  106  contains radial slots  104  which allow radial movement of the vanes  102  allowing the vanes  102  to follow the cam  108  inner surface as they are rotated by the rotor  106 . The rotor vane slots  104  have terminal cavities  116  at the inboard end to provide clearance for the vanes  102  as they move radially as the vanes follow the cam inside surface  110 . 
         [0004]    The port plates incorporate flow passages (not shown) to connect the under-vane terminal cavities  116  to the inlet and discharge passages as appropriate. This porting typically assures that the vanes  102  see the same pressure on the tips and the bottoms in the inlet and discharge arcs. In the inlet and discharge arc the leading and trailing vane  102  faces, e.g., relative to the direction of rotation of the rotor  106 , will be exposed to the same pressure, e.g., both at discharge pressure or both at inlet pressure. In major dwell arcs the vane  102  faces will see discharge pressure on the leading face and inlet pressure on the trailing face. In minor dwell arcs the vane  102  faces will see inlet pressure on the leading face and discharge pressure on the trailing face. In the major and minor dwell arcs the conventionally balanced vanes control the geometry so that the peak of the crown radius (seal point) occurs at the centerline plane of the vane  102  tip and results in high pressure on approximately 50% of the vane  102  tip. In the major dwell the high pressure is applied from the centerline plane to the leading edge of the vane  102 . In the minor dwell the high pressure is applied from the centerline plane to the trailing edge of the vane  102 . This results in a radial pressure imbalance of approximately 50% of the vane  102  thickness times the vane  102  width that positively loads the vane  102  into the cam inner surface  110 . At the balance point at the center of the vane  102 , the pressure differential on either face of the vane  102  reverses between the major and minor dwells, e.g., the discharge pressure is on the leading face in the major dwell and trailing face in the minor dwell. The centripetal force due to the mass of the vane  102  being rotated adds to the radial hydraulic imbalance force, increasing the vane  102  contact force on the cam inner surface  110 . In the inlet and discharge arcs, dynamic forces due to acceleration from the radial motion and centripetal forces acting on the mass of the vane  102  and frictional forces can further increase the vane  102  contact force on the cam inner surface  110  since the vanes  102  are hydraulically balanced. 
         [0005]    In the conventionally balanced vane  102  the 50% hydraulic imbalance and high centripetal force generally results in relatively high stresses in the major and minor dwell arcs when the inlet pressure contacts over half the vane  102  tip and discharge pressure contacts the bottom of the vane  102 . The contact in the inlet and discharge arcs is substantially lower since there is relatively little hydraulic imbalance. 
         [0006]    Another design consideration is the location and movements of the contact point on the crown radius relative to the vane  102  centerline plane as the vane  102  is rotated through the inlet, major dwell, discharge arc and the minor dwell. The contact point of the vane  102  crown radius to the cam inner surface  110  is the common tangency point of the two radii of curvature of the surface  110 . Conceptually, this point is established by a line that passes through the center point that the cam  108  is generated from and the center point of the vane  102  tip crown radius. The movement of the contact point is driven by combinations of vane geometry, crown radius, rotor slot location, vane tipping in the rotor slot  104 , and in the inlet and discharge arcs, the cam  108  tangency radii at the point of contact. The conventionally balanced vane  102  contact point is typically on the rotational centerline plane in the major and minor dwell arcs and at the maximum departure from this plane at the mid points of the inlet and discharge arcs since the cam  108  surface radii is varying between the major and minor radii in these arcs. In addition the pressures acting on the vane  102  faces in a circumferential direction and cam  108  to vane  102  tip frictional forces vary through rotation of the vane  102  in the various arcs and cause the vane  102  to either tip backward, forward or parallel to the rotor slot  104  edges. 
         [0007]    A number of prior designs have added a circumferential extension beyond the main radial shank of the vane giving the vane a “club head” or inverted ‘L” cross-sectional, as are described in U.S. Pat. No. 3,711,227, U.S. Pat. No. 3,054,357, and U.S. Pat. No. 7,637,724. 
         [0008]    A number of designs have altered the vane tip geometry to cause the seal point to be at or near the leading edge of the vane  102  in the major and minor dwell arcs. Such designs are described by U.S. Pat. No. 3,711,227 and U.S. Pat. No. 7,637,724. 
       SUMMARY 
       [0009]    In general, this document describes dual-lobe vane style positive displacement high pressure (HP) pumps. 
         [0010]    In a first aspect, a fluid pump includes a housing having an inlet port and an outlet port, a cam block having an inner surface comprised of two minor radii different from two major radii on the common center axis, and four developed curved surfaces connecting the two minor radii with the two major radii. The fluid pump also includes a collection of vanes, each vane having a vane shank having a leading shank edge and a trailing shank edge, and a vane head having a curved outer side, the curved side in contact with the cam block inner surface to separate a corresponding high fluid pressure region of a collection of high pressure regions from a corresponding low pressure region of a collection of low pressure regions. The fluid pump also includes a rotor having a central axis substantially aligned with the center axis of the cam block inner surface and including a collection of vane slots, each vane slot having a leading slot edge, a trailing slot edge substantially parallel to the leading slot edge, and spaced apart from the leading slot edge to accommodate the vane shank of one of the collection of vanes, a cavity at the radial inboard side of each slot forming a fluid path within the vane slot, and fluid flow passages axially disposed on each side of the cam block with fluid passages communicating with the housing inlet and outlet ports and cavities formed by the cam inner surface, the rotor outside diameter and adjacent vanes and rotor cavities at the inboard side of each vane slot, wherein each vane of the collection of vanes contacts the cam block inner surface at a contact point on the vane head controlled by the rotor vane slot position and the vane head outer curved surface, the contact point being located relative to the vane shank edge when the vane is radially aligned with the major radius and minor radius, and the contact point being located rotationally to create a controlled radial force between the vane head curved surface and the cam block inner surface. 
         [0011]    Various embodiments can include some, all, or none of the following features. For each vane of the collection of vanes, the vane shank can have a vane longitudinal axis that is offset from the central axis of the rotor. For each vane of the collection of vanes, the leading shank edge can be substantially parallel to the leading slot edge when the vane is radially aligned with the minor radius, and the leading shank edge is tipped in the vane slot such that it is not parallel to the leading slot edge when the vane is radially aligned with the major radius. An upper end of the vane shank can be in contact with one of the leading slot edge or trailing slot edge, and a lower end of the vane shank can be in contact with the other of the leading slot edge or the trailing slot edge. For each vane of the collection of vanes, the vane head can extend away from the trailing shank edge at an angle substantially perpendicular to the trailing shank edge. The rotor can also include a collection of fluid ports, each of the collection of fluid ports in fluid communication between a cavity of a vane slot and a high pressure fluid region of the collection of high pressure regions, substantially adjacent to the cavity. The curved outer side can be generated from an axis located on the leading edge of the vane shank. The leading slot edge can be substantially in radial alignment with the central axis. The curved outer side can be generated from an axis offset a predetermined distance in a direction of rotation from the leading slot edge. 
         [0012]    The systems and techniques described here may provide one or more of the following advantages. First, a system can provide high pumping efficiency. Second, the system can operate with reduced internal stresses and friction. Third, the system can provide increased performance and/or pump lifespan. 
         [0013]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is a cross-sectional diagram of an example prior art vane pump. 
           [0015]      FIG. 2  is a cross-sectional diagram of an example balanced clubhead vane pump. 
           [0016]      FIGS. 3A and 3B  are close-up cross-sectional diagrams of an example balanced clubhead vane pump. 
           [0017]      FIG. 4  is a cross-sectional diagram of another example balanced clubhead vane pump. 
           [0018]      FIGS. 5A and 5B  are close-up cross-sectional diagrams of another example balanced clubhead vane pump. 
           [0019]      FIG. 6  is a cross-sectional diagram of another example balanced clubhead vane pump. 
           [0020]      FIG. 7  is a cross-sectional diagram of another example balanced clubhead vane pump. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    This document describes examples of clubhead vane fluid pumps that include substantially balanced vanes. The example pumps use predetermined vane geometries, predetermined rotor slot geometries, and club-shaped vane tip features that, in some embodiments, can reduce internal stresses and wear, and/or improve pump performance. 
         [0022]      FIG. 2  is a cross-sectional diagram of an example balanced clubhead vane pump  200 . The pump  200  is a dual lobe vane style positive displacement high pressure (HP) pump. The pump  200  includes a collection of clubhead vanes  202 , each of the clubhead vanes  202  being located within a corresponding rotor slot  204  formed about the periphery of a rotor  206 . The rotor  206  and vanes  202  are contained inside a cam  208 . 
         [0023]    The rotor  206  and vanes  202  of the example balanced clubhead vane pump  200  are located between two port plates (not shown). The rotor  206 , vanes  202 , cam  208 , and port plates are placed between two backing plates (not shown) which contain porting passages to interface with a housing (not shown), allowing the separation of an inlet flow from an outlet flow. The rotor  206  is supported on a shaft  212  supported by bearings (not shown), mounted in the two backing plates, although in some embodiments other support and/or bearing arrangements are possible. The port plates, the cam  208 , and the backing covers are axially retained either by fasteners, e.g., bolts, pressure loading, or both. 
         [0024]    A collection of pumping chambers  214  of the example balanced clubhead vane pump  200  are formed by two adjacent vanes  202 , the inside surface  210  of the cam  208 , the outside surface  230  of the rotor  206  and the port plate axial surfaces. The pumping action is created by the change in length of the radius between the center of the shaft  212  and the inside surface  210  of the cam  208  between a shorter length radius  220 , e.g., a minor radius, and a longer length radius  222 , e.g., a major radius. 
         [0025]    The inside surface  210  of the example balanced clubhead vane pump  200  may be conceptually divided into eight zones. Two inlet arcs  240 , positioned approximately 180 degrees opposite each other in which the length of the radius between the center of the shaft  212  and surface  210  increases from the minor radius to the major radius cause an increasing volume in the pumping chambers  214 . Two discharge arcs  242  positioned approximately 180 degrees opposite each other in which the length of the radius between the center of the shaft  212  and surface  210  decreases from the major radius to the minor radius cause a decreasing volume in the pumping chambers  214 . Two major dwell arcs  244  are positioned approximately 180 degrees opposite each other situated between the inlet arcs  240  and the discharge arcs  242  in which the length of the radius between the center of the shaft  212  and surface  210  remains a constant at the major radius, e.g., little or no volume change in pumping chambers  214 . Two minor dwell arcs  246  are positioned approximately 180 degrees opposite each other situated between the discharge arcs  242  and the inlet arcs  240  in which the length of the radius between the center of the shaft  212  and surface  210  remains a constant at the minor radius, e.g., little or no volume change in pumping chambers  214 . 
         [0026]    The major dwell arcs  244  and the minor dwell arcs  246  of the example balanced clubhead vane pump  200  provide a substantially sealed chamber between inlet and discharge. The port plates include porting surfaces (not shown) on their periphery that are timed with the cam  208 , the rotor  206 , and the vanes  202  to provide flow into and out of the pumping chambers  214 . The port plates also conduct the flow from the pumping chambers  214  into passages in the backing plates, which are connected to the appropriate inlet and discharge passages in a housing (not shown). The port plates are timed to substantially seal the major and minor dwell arcs  244 ,  246 . The rotor  206  includes radial rotor slots  204  which allow radial movement of the vanes  202 , allowing a line on the vane head  207  crown radius to remain in contact with the inner surface  210  as the vanes  202  are rotated by the rotor  206 . The rotor vane slots  204  have terminal cavities  216  at the inboard end to provide clearance for the vanes  202  as they move radially inward in the discharge arcs  242  and also allow porting of fluid displaced by this vane motion in the inlet and discharge arcs  240 ,  242 . The rotor  206  is rotated by the shaft  212  and urges the vanes  202  to rotate relative to the cam  208 . The vanes  202  contact the inner surface  210  at a line on the crown radius to form a sliding seal with the inner surface  210 , completing the pumping chambers  214 . 
         [0027]      FIGS. 3A and 3B  are close-up cross-sectional diagrams of the example balanced clubhead vane pump  200 . As can be seen in greater detail in these figures, the clubhead vane  202  includes a vane shank  306  that extends into the rotor slot  204 , and a head  307  that extends substantially perpendicular to the vane shank  306  at a radially distal end of the vane  202 , extending from the vane  202  in a generally trailing orientation relative to a direction of rotor rotation, as indicated by arrow  201 . The head  307  includes a surface  319  formed with a crown radius  312 . In general, to address the vane balancing problems of the pump  100  of  FIG. 1 , the geometry of the vane  202  is modified by controlling a crown radius axis  314  of the vane crown radius  312  relative to the edges  304 ,  308  of the vane  202  in conjunction with an edge  305  and an edge  309  of the rotor slot  204  edges relative to a center line of rotation  320  for the rotor  206 . By controlling geometries of the tip of the vane  202 , the crown radius axis  314 , and the rotor slot edges  305  and  309 , the contact point  302  between the vane crown radius  312  and the cam inner surface  210  can be controlled. 
         [0028]    Referring to  FIG. 3A , one of the clubhead vanes  202  of the example balanced clubhead vane pump  200  is shown in one of the major dwell arcs  244 . The cam contact point  302  in the major dwell arc  244  is in advance of the trailing edge  304  of the vane shank  306 , or trailing the leading edge  308  of the vane shank  306 . 
         [0029]    Selective design of the geometry of the vane  202  and the rotor slot  204  of the example balanced clubhead vane pump  200  can cause the contact point  302  in the major dwell arc  244  to be in advance of the trailing edge  304  of the vane shank  306 , as indicated by dimension line  360 , or trailing the leading edge  308  of the vane shank  306 . Referring now to  FIG. 3B , in the minor dwell arc  246  of the example balanced clubhead vane pump  200  the seal point  302  is located slightly forward or backward, as indicated by the dimension line  362 , relative to the vane shank  306  due to changes in the cam  208  radii and tipping of the vane  202  in the rotor slot  204 . In some embodiments, this change in the location of the sealing point  302  between the major dwell arcs  244  as shown in  FIG. 3A , and the minor dwell arcs  246  as can be seen in  FIG. 3B , can be used for improved vane hydraulic balancing, e.g., compared to the pump  100  of  FIG. 1 , since the vane shank  306  under-vane surface is ported to discharge pressure in the major dwell arc  244  or inlet pressure in the minor dwell arc  246 , or vice versa, providing a slight hydraulic imbalance of the vane crown radius  312  into the cam inner surface  210  and provide a substantially positive seal between pumping chambers  214 . 
         [0030]    In the illustrated example balanced clubhead vane pump, the leading edge  309  of the slot  204  is radially aligned with the rotor centerline  320 . The vane  202  is formed with an inverted “club head” vane shape, with the crown radius axis  314  selected to cause the contact point  302  to slightly lead the vane shank  306  trailing edge  304  plane when the vane  202  is in the major dwell arc  244 . The “club head” shaped head  307  of the vane  202  overhangs the vane shank trailing edge  304 . In some implementations, this vane  202  configuration can be referred to as having a “vane with trailing edge balance” (VTEB) and a rotor  206  with offset slots  204  having the “rotor slot leading edge on centerline” (RSLECL). In some embodiments, this type of geometry can provide numerous possible combinations of rotor slot  202  and head  307  balance points when compared to the leading edge  309  and trailing edge  305  locations relative to the centerline  320 . 
         [0031]    As illustrated by  FIG. 3A , the vane  202  of the example balanced clubhead vane pump  200  is designed in conjunction with the cam surface  210  geometry and the rotor  206  such that, in the major dwell arcs  244  of the cam  208 , the contact point  302  occurs on the surface  319 , the small dimension  360 , in advance of the projected plane of the trailing edge  304  of the shank  306  of the vane  202 . A vane longitudinal axis of the vane  202 , represented by the line AA, is offset from the central axis of the rotor and the rotational centerline  320 . The contact point  302  provides the pressure seal point between high and low pressure, with the portion of the surface  319  in advance of the contact point  302  exposed to relatively high pressure and the portion of the surface  319  following the contact point  302  exposed to relatively low pressure. 
         [0032]    Since the contact point  302  is in advance of the trailing edge  304  plane and the bottom of the vane shank  306  is exposed to high pressure, a small hydraulic imbalance is created urging the vane  202  into contact with the inner surface  210 . Porting of the terminal cavity  216  maintains the bottom of the vane shank  306  substantially at discharge pressure in the major dwell arc  244 . The geometry of the cam  208 , vane  202 , and rotor  206  controls the small angle between the rotational centerline  320 , e.g., set by the rotor slot leading edge  309  substantially aligned with the centerline  320 , and a conceptual line passing through the vane crown radius axis  314  by selecting the positions of both the rotor slot edges  305 ,  309 , and the crown radius axis  314  to the vane shank edges  304 ,  308 . The small dimension  360  on the crown surface  319  relative to the vane shank edges  304 ,  308  is decreased by the tipping angle of the vane  202  in the rotor slot  204 . The dimensional relationship between the vane crown radius axis  314  and the edges  304 ,  308  of the vane shank  306  and edges  305 ,  309  of rotor slot  204  of the example balanced clubhead vane pump is selected to control this small angle and the location of the contact point  302  in advance of the vane shank trailing edge  304  plane. The combination of this small angle in conjunction with backward, e.g., cross corner, tipping of the vane shank  306  in the rotor slot  204  causes the contact point  302  to be located in advance of the vane shank trailing edge  304  plane as shown in  FIG. 3A . 
         [0033]    Referring to  FIG. 3B , in one of the minor dwell arcs  246  of the example balanced clubhead vane pump, the seal point  302  on the surface  319  will shift slightly forward or backward relative to the vane shank  306  due to changes in the radii of the inner surface  210  and tipping of the vane  202  in the rotor slot  204 . This change in the sealing point  302  between the major dwell arc  244  and the minor dwell arc  246  provides hydraulic balancing of the vane  202  since the vane shank  306  under-vane surface is ported to discharge pressure in the major dwell arc  244  or inlet pressure in minor dwell arc  246 , or vice versa, to provide a slight hydraulic imbalance in these arcs urging the vane crown radius into the cam inner surface  210  to provide a substantially positive seal. 
         [0034]    Still referring to  FIG. 3B , the example balanced clubhead vane pump  200  is illustrated with the vane  202  positioned in the minor dwell arc  246 . In the minor dwell arc  246  the vane  202  and the rotor  206  geometry results in a slightly larger angle which moves the contact point  302  on surface  319  toward the trailing edge  304  of the vane  202 . The vane longitudinal axis represented by the line AA, is offset from the central axis of the rotor and the rotational centerline  320 . The circumferential pressure forces acting on the vane  202  cause it to load onto the leading edge  309  of the rotor slot  204 , in which the leading edge  308  of the vane  202  is substantially aligned with the slot leading edge  309 , e.g., no tipping of the vane  202 . This causes the contact point  302  to move to a position that is trailing the vane shank trailing edge  304  by the small dimension  362 . In this configuration, the contact point  302  in the minor dwell arc  246  is at a point trailing the vane shank trailing edge  304  plane. 
         [0035]    Since the under-side of the head  307  in this region is at discharge pressure, and the small dimension  362  is at low pressure a small imbalance force is generated to assist loading the vane  202  onto the inner cam surface  210 . When the vane  202  is in the minor dwell arc  246 , porting of the terminal cavities  216  maintains the bottom of the shank  306  at inlet pressure. In the inlet arcs  240  and discharge arcs  242 , the under vane pressures are substantially matched to the over vane pressures as in a conventional pump, and there is substantially no hydraulic imbalance. Centripetal forces cause the vanes  202  to track the cam inner surface  210 . 
         [0036]      FIG. 4  is a cross-sectional diagram of another example balanced clubhead vane pump  400 . The pump  400  is a dual lobe vane style positive displacement high pressure (HP) pump. The pump  400  includes a collection of clubhead vanes  402 , each of the vanes  402  being located within a corresponding rotor slot  404  formed about the periphery of a rotor  406 . The rotor  406  and vanes  402  revolve inside a cam  408 . The rotor  406  is supported on a shaft  412 . 
         [0037]    A collection of pumping chambers  414  of the example balanced clubhead vane pump  400  are formed by two adjacent vanes  402 , the inside surface  410  of the cam  408 , the outside surface  430  of the rotor  406  and port plate axial surfaces (not shown). Pumping action is created by the change in length of the radius between the center of the shaft  412  and the inside surface  410  of the cam  408  between a smaller radius  420 , e.g., minor radius, and a larger radius  422 , e.g., major radius. 
         [0038]    As will be shown in additional detail in  FIGS. 5A and 5B , the example balanced clubhead vane pump  400  is substantially similar to the pump  200 , except that the vanes  402  are reversed, e.g., the club-shaped heads protrude from the vane in the leading direction rather than in the trailing direction as they do in the example pump  200 . 
         [0039]      FIGS. 5A and 5B  are close-up cross-sectional diagrams of the example balanced clubhead vane pump  400 . As can be seen in greater detail in these figures, the clubhead vane  402  includes a vane shank  506  that extends into the rotor slot  404 , and a head  507  that extends substantially perpendicular to the vane shank  506  at a radially distal end of the vane  402 , extending from the vane  402  in a generally leading orientation. The head  507  includes a surface  519  formed with a crown radius  512 . The geometry of the vane  402  is modified by controlling a crown radius axis  514  of the vane crown radius  512  relative to the edges  504 ,  508  of the vane  402  in conjunction with an edge  505  and an edge  509  of the rotor slot  404  edges relative to a center line of rotation  520  for the rotor  406 . By controlling geometries of the tip of the vane  402 , the crown radius axis  514 , and the rotor slot edges  505  and  509 , the location of the contact point  502  between the vane crown radius  512  and the cam inner surface  410  can be controlled. 
         [0040]    Referring to  FIG. 5A , one of the clubhead vanes  402  of the example balanced clubhead vane pump  400  is shown in a major dwell arc. The cam contact point  502  in the major dwell arc  244  is slightly in advance of a leading edge  508  of the vane shank  506 , as indicated by dimension line  560 . 
         [0041]    Referring now to  FIG. 5B , one of the clubhead vanes  402  of the example balanced clubhead vane pump  400  is shown in a minor dwell arc. In the minor dwell arc the seal point  502  is located substantially along the plane of the leading edge  508  of the vane shank  506 , as indicated by the dimension line  562 , due to changes in the cam  508  radii and tipping of the vane  402  in the rotor slot  404 . In some embodiments, this change in the location of the sealing point  502  between the major dwell arcs and the minor dwell arcs can be used for vane hydraulic balancing since the full vane shank  506  under-vane surface is ported to discharge pressure in the major dwell arc or inlet pressure in the minor dwell arc, or vice versa, providing a slight hydraulic imbalance in these arcs of the vane crown radius  512  into the cam inner surface  510  and provide a positive seal between pumping chambers  414 . 
         [0042]      FIG. 6  is a cross-sectional diagram of another example balanced clubhead vane pump  600 . The example clubhead vane pump  600  is a modification of the example balanced clubhead vane pump  200 , in which the pressures within the collection of terminal cavities  216  can be substantially the same as the pressure in the pumping chamber  214  in advance of the vane  202 . A rotor  606  is substantially similar to the rotor  206 , with the addition of a collection of passages  602  in the rotor  606 . The passages  602  communicate the pressures in the chambers  214  leading the vanes  202  into the under-vane terminal cavities  216 . 
         [0043]      FIG. 7  is a cross-sectional diagram of another example balanced clubhead vane pump  700 . The example balanced clubhead vane pump  700  is another modification of the example pump  200 , in which the pressures within the collection of terminal cavities  216  can be substantially the same as the pressure in the pumping chambers  214  in advance of a collection of vanes  702 . The vanes  702  are substantially similar to the vanes  202 , except that the vanes  702  include a fluid passage  704  on the leading edge of their vane shanks. The passages  704  communicate the pressures in the chambers  214  leading the vanes  702  into the under-vane terminal cavities  216 . 
         [0044]    In some embodiments of the example balanced clubhead vane pumps  600  and  700 , by providing the passages  602  and/or  704 , the ports of the under-vane terminal cavities  216  can be simplified. In some embodiments, the under-vane pressure and over-vane pressure can change proportionally, reducing possible over or under radial balances of the vanes  202  and/or  702 . In some embodiments, the configurations of pump  600  and/or  700  can be used to reduce the need for under-vane kidneys in port plates and/or to reduce the need for port plates. 
         [0045]    Although a few implementations have been described in detail above, other modifications are possible. For example, numerous other possible combinations of rotor slot edge positions relative to rotational centerlines and crown radius generation center points with respect to the vane shank edges may be used. In some embodiments, the vane crown radius contact points can be set to balance on either the leading edge or trailing edge of the vanes. In some embodiments, the balanced clubhead vane pumps  200 ,  400 ,  600 , and/or  700  can be dual lobe cam fixed displacement vane pumps, single lobe fixed displacement vane pumps or multiple lobe fixed displacement vane pumps. In some embodiments, the design features described herein may also be applied to variable vane pumps implementing either single or multiple lobe style cams. In some examples, other components may be added to, or removed from, the described systems. Accordingly, other implementations are within the scope of the following claims.