Abstract:
A double mechanical seal assembly for sealing around the shaft of a centrifugal pump, a shaft sleeve that surrounds a portion of the shaft, and has an inner surface with a notch, the notch corresponding to a key on the shaft that engages the notch to transmit torque from the shaft to the shaft sleeve, an annular seal sleeve that surrounds the shaft sleeve and is engaged with the shaft sleeve, and rotating inboard outboard seals, each having a rotating seal face and operably associated. The seal assembly also includes stationary inboard and outboard seals each having a stationary seal face, the stationary seal face of the stationary inboard seal sealingly engaged with the rotating seal face of the rotating inboard seal and the stationary seal face of the stationary outboard seal sealingly engaged with the rotating seal face of the rotating outboard seal.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Application No. 61/919,353, titled “Double Mechanical Seal Chamber for Pumps” and filed on Dec. 20, 2013, the contents of which are incorporated herein by reference in its entirety. This application is also related to U.S. patent application Ser. No. ______, titled “Coverplates for Centrifugal Pumps” and filed on Dec. 20, 2014, which claims priority to U.S. Provisional Application No. 61/919,274, the contents both of which are incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments disclosed herein relate to seals for use in pumps. In particular, embodiments disclosed herein relate to dual mechanical seals with novel cooling and axial adjustment capabilities. 
         [0004]    2. Description of Related Art 
         [0005]    Centrifugal pumps are often used in oilfield applications, such as, for example, to pump fluids into a wellbore during hydraulic fracturing operations. Typically, such centrifugal pumps include an impeller within a pump housing that rotates to drive fluids through the pump. The impeller is turned by a shaft that enters the pump housing through a stuffing box. A seal is employed at the interface between the shaft and the stuffing box, to prevent fluids from leaking from the pump. 
         [0006]    Typically, the seals used in a centrifugal pump in a hydraulic fracturing operation have very tight tolerances between seal faces, and are cooled by the hydraulic fracturing fluid being pumped through the pump housing. The seal faces are typically very close together and have a very high coefficient of friction. One problem with relying on pumped fluid to cool the seal faces is that if there is even a minor loss of flow in the pump, the seal faces can very quickly heat up to a level that will destroy the seal. This problem can be exacerbated by an operator trying to reverse the damage by reintroducing cool fluid to the overheated seal surfaces, which can lead to cracking and further destruction of the surfaces. After such a failure of the seal, the only option to take the pump off-line and repair or replace the seal. Accordingly, one weakness of known pumps is that the seals can easily overheat based on operator error or otherwise. 
         [0007]    In addition, the hydraulic fracturing fluids typically pumped at a well site are very abrasive and corrosive, which leads to wear on the impeller. As the impeller wears, a gap can form between the impeller and the pump housing, leading to inefficiencies in the pump. One solution to such impeller wear is to adjust the position of the impeller, by extending the shaft that turns the impeller, inwardly toward the pump housing, to close this gap. The problem with this solution, however, is the low tolerance of known seals to such a realignment of the shaft and impeller. Most seals are able to move axially only a few hundredths of an inch before the seal is compromised. Accordingly, a second weakness of known pumps is an inability to adjust the position of the shaft and impeller relative to the pump housing without damaging or destroying the seal. 
         [0008]    Furthermore, because fluids pumped in hydraulic fracturing operations are abrasive, and often contain solid particles, such particles can get clogged or build up in the stuffing box around the axle. Such buildup can lead to seal damage because it can impede the flow of pumped fluid into the stuffing box to cool the seal. Accordingly, a third weakness of known pumps is the buildup of particles and other contaminates in the stuffing box. 
       SUMMARY OF THE INVENTION 
       [0009]    One embodiment of the present invention provides a double mechanical seal assembly for sealing around the shaft of a centrifugal pump, the centrifugal pump having a pump frame. The seal assembly includes an annular shaft sleeve that surrounds a portion of the shaft, the annular shaft sleeve having an inner surface with a notch, the notch corresponding to a key on the shaft that engages the notch to transmit torque from the shaft to the shaft sleeve, and an annular seal sleeve that surrounds at least a portion of the shaft sleeve and is engaged with the shaft sleeve so that as the shaft and the shaft sleeve rotate, the seal sleeve rotates. The seal assembly further includes a rotating inboard seal and a rotating outboard seal each having a rotating seal face and operably associated with the shaft sleeve so that as the shaft sleeve rotates, the rotating inboard seal and the rotating outboard seal rotate, as well as a stationary inboard seal and a stationary outboard seal each having a stationary seal face, the stationary seal face of the stationary inboard seal sealingly engaged with the rotating seal face of the rotating inboard seal and the stationary seal face of the stationary outboard seal sealingly engaged with the rotating seal face of the rotating outboard seal, the stationary inboard seal and stationary outboard seal decoupled from the shaft and the shaft sleeve so that they do not rotate as the shaft and the shaft sleeve rotate. 
         [0010]    In some embodiments, the double mechanical seal assembly can further include a gland plate surrounding a portion of the shaft sleeve and fixedly attached to the pump frame, the gland plate having a coolant inlet port for injection of coolant into the seal assembly to help cool the inboard and outboard seal faces, and an outlet port to permit egress of coolant after circulation through the seal assembly. In addition, the seal assembly can include a spring holder surrounding the seal sleeve and axially positioned between the inboard seals and the outboard seals with an inboard end contacting the stationary inboard seal, the spring holder having a plurality of springs extending axially from an outboard end thereof, an outboard end of the springs fixed in position relative to the gland plate so that the springs push the spring holder axially in an inboard direction, in turn pushing the stationary inboard seal into sealing engagement with the rotating inboard seal. The springs can have sufficient tension to maintain sealed engagement between stationary inboard seal and the rotating inboard seal as the spring holder moves axially in an inboard direction relative to the gland plate. 
         [0011]    In alternate embodiments the springs can have sufficient tension to maintain sealed engagement between stationary inboard seal and the rotating inboard seal as the spring holder moves up to at least about 0.25 inches in an inboard direction relative to the gland plate. Furthermore, the stationary inboard seal face and the rotating inboard seal face can be made of tungsten, the stationary outboard seal face can be made of carbon, and the rotating outboard seal face can be made of silicon carbide (SiC). 
         [0012]    Another embodiment of the present invention provides a double mechanical seal assembly for sealing around the shaft of a centrifugal pump, the centrifugal pump having a pump frame. The seal assembly includes an annular shaft sleeve that surrounds a portion of the shaft and that is mechanically engaged with the shaft so that as the shaft rotates the shaft sleeve rotates, and an annular seal sleeve that surrounds at least a portion of the shaft sleeve and is engaged with the shaft sleeve so that as the shaft and the shaft sleeve rotate, the seal sleeve rotates. The seal assembly also includes a rotating inboard seal and a rotating outboard seal each having a rotating seal face and operably associated with the shaft sleeve so that as the shaft sleeve rotates, the rotating inboard seal and the rotating outboard seal rotate, as well as a stationary inboard seal and a stationary outboard seal each having a stationary seal face, the stationary seal face of the stationary inboard seal sealingly engaged with the rotating seal face of the rotating inboard seal and the stationary seal face of the stationary outboard seal sealingly engaged with the rotating seal face of the rotating outboard seal, the stationary inboard seal and stationary outboard seal decoupled from the shaft and the shaft sleeve so that they do not rotate as the shaft and the shaft sleeve rotate. Furthermore, the seal assembly includes a gland plate surrounding a portion of the shaft sleeve and fixedly attached to the pump frame, the gland plate having a coolant inlet port for injection of coolant into the seal assembly to help cool the inboard and outboard seal faces, and an outlet port to permit egress of coolant after circulation through the seal assembly. 
         [0013]    In some example embodiments, the annular shaft sleeve can have an inner surface with a notch, the notch corresponding to a key on the shaft that engages the notch to transmit torque from the shaft to the shaft sleeve. In some embodiments, the seal assembly can further include a spring holder surrounding the seal sleeve and axially positioned between the inboard seals and the outboard seals with an inboard end contacting the stationary inboard seal, the spring holder having a plurality of springs extending axially from an outboard end thereof, an outboard end of the springs fixed in position relative to the gland plate so that the springs push the spring holder axially in an inboard direction, in turn pushing the stationary inboard seal into sealing engagement with the rotating inboard seal. The springs can have sufficient tension to maintain sealed engagement between stationary inboard seal and the rotating inboard seal as the spring holder moves axially in an inboard direction relative to the gland plate. In some instances, the springs can have sufficient tension to maintain sealed engagement between stationary inboard seal and the rotating inboard seal as the spring holder moves up to at least about 0.25 inches in an inboard direction relative to the gland plate. 
         [0014]    In some embodiments, the stationary inboard seal face and the rotating inboard seal face can be made of tungsten, the stationary outboard seal face can be made of carbon, and the rotating outboard seal face can be made of silicon carbide (SiC). 
         [0015]    Yet another embodiment of the invention provides a double mechanical seal assembly for sealing around the shaft of a centrifugal pump, the centrifugal pump having a pump frame. The seal assembly includes an annular shaft sleeve that surrounds a portion of the shaft and that is mechanically engaged with the shaft so that as the shaft rotates the shaft sleeve rotates, and an annular seal sleeve that surrounds at least a portion of the shaft sleeve and is engaged with the shaft sleeve so that as the shaft and the shaft sleeve rotate, the seal sleeve rotates. The seal assembly further includes a rotating inboard seal and a rotating outboard seal each having a rotating seal face and operably associated with the shaft sleeve so that as the shaft sleeve rotates, the rotating inboard seal and the rotating outboard seal rotate, as well as a stationary inboard seal and a stationary outboard seal each having a stationary seal face, the stationary seal face of the stationary inboard seal sealingly engaged with the rotating seal face of the rotating inboard seal and the stationary seal face of the stationary outboard seal sealingly engaged with the rotating seal face of the rotating outboard seal, the stationary inboard seal and stationary outboard seal decoupled from the shaft and the shaft sleeve so that they do not rotate as the shaft and the shaft sleeve rotate. 
         [0016]    Furthermore, the seal assembly includes a gland plate surrounding a portion of the shaft sleeve and fixedly attached to the pump frame, and a spring holder surrounding the seal sleeve and axially positioned between the inboard seals and the outboard seals with an inboard end contacting the stationary inboard seal, the spring holder having a plurality of springs extending axially from an outboard end thereof, an outboard end of the springs fixed in position relative to the gland plate so that the springs push the spring holder axially in an inboard direction, in turn pushing the stationary inboard seal into sealing engagement with the rotating inboard seal. The springs have sufficient tension to maintain sealed engagement between stationary inboard seal and the rotating inboard seal as the spring holder moves axially in an inboard direction relative to the gland plate. 
         [0017]    In some embodiments, the springs can have sufficient tension to maintain sealed engagement between stationary inboard seal and the rotating inboard seal as the spring holder moves up to at least about 0.25 inches in an inboard direction relative to the gland plate. In addition, the annular shaft sleeve can have an inner surface with a notch, the notch corresponding to a key on the shaft that engages the notch to transmit torque from the shaft to the shaft sleeve. 
         [0018]    In some alternate embodiments, the gland plate can have a coolant inlet port for injection of coolant into the seal assembly to help cool the inboard and outboard seal faces, and an outlet port to permit egress of coolant after circulation through the seal assembly. Furthermore, the stationary inboard seal face and the rotating inboard seal face can be made of tungsten, the stationary outboard seal face can be made of carbon, and the rotating outboard seal face can be made of silicon carbide (SiC). 
         [0019]    Other embodiments of the present invention provide a stuffing box for a centrifugal pump. The stuffing box includes an inboard side for engagement with a pump housing of the centrifugal pump, an outboard side opposite the inboard side, and a passageway between the inboard side and outboard side of the stuffing box, the passageway for insertion of the shaft and a portion of the seal assembly. The passageway has an inner passageway surface that includes ribs formed in the inner passageway surface and extending inwardly from the inner passageway surface toward the shaft. The ribs are arranged circumferentially around the inner passageway surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The present technology will be better understood on reading the following detailed description of nonlimiting embodiments thereof, and on examining the accompanying drawings, in which: 
           [0021]      FIG. 1  shows a top view of a centrifugal pump according to an embodiment of the present invention; 
           [0022]      FIG. 2  shows an isometric exploded view of the pump of  FIG. 1 ; 
           [0023]      FIG. 3A  shows a side view of a stuffing box according to an embodiment of the present invention; 
           [0024]      FIG. 3B  shows a cross-sectional view of the stuffing box of  FIG. 3A  taken along line  3 B- 3 B; 
           [0025]      FIG. 3C  shows a cross-sectional view of the stuffing box of  FIG. 3A  taken along line  3 C- 3 C; 
           [0026]      FIG. 3D  shows a cropped view of the passageway and ribs of the stuffing box of  FIGS. 3A-3C ; 
           [0027]      FIG. 4  shows a side cross-sectional view of a seal assembly according to an embodiment of the present invention taken along line  4 - 4  of  FIG. 2 ; 
           [0028]      FIG. 5A  is a side view of the seal assembly of  FIG. 4 ; 
           [0029]      FIG. 5B  is an end view of the seal assembly of  FIG. 5A ; 
           [0030]      FIG. 6A  is an end view of the shaft sleeve according to an embodiment of the present invention; 
           [0031]      FIG. 6B  is a side cross-sectional view of the shaft sleeve of  FIG. 6A  taken along line  6 B- 6 B; 
           [0032]      FIG. 6C  is an alternate end view of the shaft sleeve of  FIGS. 6A and 6B ; 
           [0033]      FIG. 7A  is an end view of a seal sleeve according to an embodiment of the present invention; 
           [0034]      FIG. 7B  is a side cross-sectional view of the seal sleeve of  FIG. 7A ; 
           [0035]      FIG. 7C  is an alternate end view of the seal sleeve of  FIGS. 7A and 7B ; 
           [0036]      FIG. 7D  is an enlarged side cross-sectional view of a portion of the seal sleeve of  FIG. 7B  indicated by area  7 D; 
           [0037]      FIG. 8A  is a side cross-sectional view of a rotating inboard seal carrier according to an embodiment of the present invention; 
           [0038]      FIG. 8B  is an end view of the rotating inboard seal carrier of  FIG. 8A ; 
           [0039]      FIG. 8C  is an enlarged side cross-sectional view of a portion of the rotating inboard seal carrier of  FIG. 8A , as indicated by area  8 C; 
           [0040]      FIG. 8D  is an end view of a rotating inboard seal; 
           [0041]      FIG. 8E  is a side view of the rotating inboard seal of  FIG. 8D ; 
           [0042]      FIG. 9A  is an end view of a stationary inboard seal carrier according to an embodiment of the present invention; 
           [0043]      FIG. 9B  is a side cross-sectional view of the stationary inboard seal carrier of  FIG. 9A  taken along line  9 B- 9 B; 
           [0044]      FIG. 9C  is an enlarged side cross-sectional view of a portion of the stationary inboard seal carrier of  FIG. 9B  as indicated by area  9 C; 
           [0045]      FIG. 9D  is an end view of a stationary inboard seal; 
           [0046]      FIG. 9E  is a side view of the stationary inboard seal of  FIG. 9D ; 
           [0047]      FIG. 10A  is an end view of a spring holder according to an embodiment of the present invention; 
           [0048]      FIG. 10B  is a side cross-sectional view of the spring holder of  FIG. 10A  taken along line  10 B- 10 B; 
           [0049]      FIG. 10C  is an enlarged side-cross-sectional view of the spring holder of  FIG. 10A  taken along line  10 C- 10 C; 
           [0050]      FIG. 10D  is a side view of the spring holder of  FIGS. 10A-10C ; 
           [0051]      FIG. 11A  is an end view of a gland plate according to an embodiment of the present invention; 
           [0052]      FIG. 11B  is a side cross-sectional view of the gland plate of  FIG. 11A  taken along line  11 A- 11 A; 
           [0053]      FIG. 11C  is a side cross-sectional view of the gland plate of  FIG. 11A  taken along line  11 C- 11 C; 
           [0054]      FIG. 11D  is a side cross-sectional view of the gland plate of  FIG. 11A  taken along line  11 D- 11 D; 
           [0055]      FIG. 11E  is an enlarged side cross-sectional view of a portion of the gland plate shown in  FIG. 11B  as indicated by area  11 E; 
           [0056]      FIG. 12A  is an end view of a snap ring according to an embodiment of the present invention; 
           [0057]      FIG. 12B  is a side view of the snap ring of  FIG. 12A ; 
           [0058]      FIG. 13A  is an end view of a spacer according to an embodiment of the present invention; 
           [0059]      FIG. 13B  is a side view of the spacer of  FIG. 13A ; 
           [0060]      FIG. 14A  is a side view of a stationary outboard seal carrier according to an embodiment of the present invention; 
           [0061]      FIG. 14B  is an end view of the stationary outboard seal carrier of  FIG. 14A ; 
           [0062]      FIG. 14C  is an end view of a stationary outboard seal; 
           [0063]      FIG. 14D  is a side view of the stationary outboard seal of  FIG. 14C ; 
           [0064]      FIG. 15A  is an end view of a rotating outboard seal carrier according to an embodiment of the present invention; 
           [0065]      FIG. 15B  is a side cross-sectional view of the rotating outboard seal carrier of  FIG. 15A  taken along line  15 B- 15 B; 
           [0066]      FIG. 15C  is an end view of a rotating outboard seal; 
           [0067]      FIG. 15D  is a side view of the rotating outboard seal of  FIG. 15C ; 
           [0068]      FIG. 16A  is an end view of a drive collar according to an embodiment of the present invention; 
           [0069]      FIG. 16B  is a side cross-sectional view of the drive collar of  FIG. 16A  taken along line  16 B- 16 B; and 
           [0070]      FIG. 16C  is a side cross-sectional view of the drive collar of  FIG. 16A  taken along line  16 C- 16 C. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0071]    The foregoing aspects, features, and advantages of the present technology will be further appreciated when considered with reference to the following description of preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. The following is directed to various exemplary embodiments of the disclosure. The embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, those having ordinary skill in the art will appreciate that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. 
         [0072]      FIG. 1  depicts a top view of a pump  20  according to an embodiment of the present invention. The pump  20  includes a pump housing  22  and a front cover  24 , as well as a bearing cover  26 , frame  28 , and shaft  30 . The pump  20  also includes a seal  32  and a stuffing box  34 . The shaft extends through the bearing cover  26  and a bearing housing  36  (shown in  FIG. 2 ) in the frame  28 , as well as the seal  32  and the stuffing box  34  where it attaches to an impeller  38  (also shown in  FIG. 2 ) disposed within the pump housing  22 . The shaft serves to turn the impeller  38 , which moves fluid through the pump. The pumped fluid can include, for example, hydrocarbons and sand that are used in hydraulic fracturing operations. 
         [0073]    In the exploded view of  FIG. 2 , the components, including some internal components, of the pump  20  are shown. In operation, the pump  20  receives fluid through a pipe (not shown) connected to the front cover  24 . The fluid enters the pump housing  22  through the front cover  24  and comes into contact with the impeller  38 . The impeller rotates within the pump housing  22  to drive fluid through the pump  20 . As shown in  FIGS. 1 and 2 , the shaft  30  that drives the impeller  38  passes through the stuffing box  34  attached to the pump housing  22  to the impeller  38 . It is necessary to seal the interface between the shaft  30  and the stuffing box  34  to prevent the egress of fluid from the pump housing  22 . This is accomplished by the use of the seal  32  in conjunction with a shaft sleeve  40  positioned between the seal  32  and the shaft  30 . 
         [0074]    The seal  32  and shaft sleeve  40  of the present invention serve to seal the interface between the shaft  30  and the stuffing box  34 , while simultaneously allowing for adjustment of the seal  32  relative to the shaft  30  without compromising the integrity of the seal  32 . This feature is advantageous because over time as the pump operates, due to the abrasive nature of the fluids in the pump, the impeller  38  wears. As it wears, the impeller  38  can become somewhat loose in the pump housing  22 . For example, a gap may form between the side of the impeller  38  and the pump housing  22 , leading to inefficiencies in the pump. In the pump  20  of the embodiment shown in  FIG. 1 , the position of the impeller  38  relative to the pump housing  22  can be adjusted by adjusting the position of the shaft  30 . 
         [0075]    For example, as shown in  FIG. 1 , the shaft  30  is axially fixed relative to the bearing housing  36 , which is in turn fastened to the frame  28  of the pump  20 . Initially, when the impeller  38  is new, the shaft  30  and bearing cover  26  may be positioned so that there is a space  42  between the bearing housing  36  and the frame  28 . As the impeller  38  wears, however, it may become necessary to adjust the position of the impeller  38  relative to the pump housing  22 . To accomplish this, the space  42  can be reduced or eliminated by moving the bearing housing  36  toward the frame  28 . This can be accomplished, for example, by tightening fasteners that attach the bearing housing  36  to the frame  28 . As the bearing housing  36  moves toward the frame  28 , the shaft moves axially toward the pump housing  22  and in turn repositions the impeller  38  within the pump housing  22  to close the gap between the impeller  38  and the pump housing  22 . As the shaft  30  moves toward the pump housing  22 , the seal  32  of the present invention is capable of axial movement along with the shaft  30  without losing the integrity of the seal  32 . In some embodiments the shaft  30  and seal  32  can move axially up to about 0.25 inch or more. 
         [0076]    In addition, as described in more detail below, the seal  32  of the present invention includes a secondary cooling mechanism to avoid the problems that many known seals face as a result of reduced fluid flow through the pump, or dead-heading. This secondary cooling mechanism circulates fluid between the seal surface to help cool the seal surfaces even in the absence of pumped fluid. 
         [0077]    Referring now to  FIGS. 3A-3D , there are shown more detailed views of the stuffing box  34 . The stuffing box  34  is designed to enclose the frame side of the pump  20  (as shown in  FIG. 1 ), and include a central passage  44  through which the shaft  30  passes and in which the shaft sleeve  40  and seal  32  at least partially reside. In the embodiment depicted in  FIGS. 3A-3D , there are ribs  46  that protrude inwardly from inner surface  48  of the central passage  44  toward the central axis A of the central passage  44 . The ribs  46  can be spaced circumferentially around the inner surface  48 . 
         [0078]    One purpose of the ribs  46  of the stuffing box is to prevent particles in the pumped fluid from accumulating inside the stuffing box. In the absence of ribs  46 , such an accumulation of particles can occur over time and the density of the particles can eventually reach a point where fluid cannot adequately access and cool the surfaces of the seal  32 . This can lead to problems of the seal  32  overheating and ultimately being damaged. The ribs  46  act to prevent the buildup of harmful particles by increasing turbulence in the stuffing box  34 , and physically breaking up large particles that may otherwise become wedged or stuck in central passage  44  of the stuffing box  34 . 
         [0079]      FIG. 4  shows the seal  32  assembly and shaft sleeve  40 , include individual components of the seal  32 . The arrangement of seal components that make up the seal  32  help to provide the ability of the seal  32  to move relative to the stuffing box  34  and pump housing  22  to allow adjustment of a worn impeller  38 , as discussed above. In particular, the seal  32  assembly shown in  FIG. 4  includes the shaft sleeve  40 , the seal sleeve  48 , the rotating inboard seal  50  and rotating inboard seal carrier  52 , the stationary inboard seal  54  and stationary inboard seal carrier  56 , the spring holder  58 , the gland plate  60 , the stationary outboard seal  62  and stationary outboard seal carrier  64 , the rotating outboard seal  66  and rotating outboard seal carrier  68 , and the drive collar  70 . Additional components included in the assembly are a snap ring  72  (shown in  FIGS. 12A and 12B ) and spacer rings  74  (shown in  FIGS. 13A and 13B ). The seal  32  assembly also includes a pin  76  that attaches to the gland plate  60  and limits movement of the seal  32  relative to the gland plate  60 .  FIGS. 5A and 5B  show the seal  32 , including the gland plate  60  in a more schematic form. 
         [0080]      FIGS. 6A-6C  show the shaft sleeve  40  according to an example embodiment of the present invention. As can be seen in  FIG. 6A , the shaft sleeve  40  includes a notch  78  in an inner surface thereof. The notch  78  of the shaft sleeve  40  corresponds to a protrusion  80  (shown in  FIG. 2 ) on the shaft  30  and acts as a torque transfer mechanism. That is, when the shaft  30  turns, the protrusion  80  engages the notch  78  of the shaft sleeve  40 , and causes the shaft sleeve  40  to turn with the shaft  30 . The shaft sleeve  40  also includes indents  82  for engagement with set screws that may be used, for example, to engage the shaft sleeve  40  with the seal sleeve  48 . Furthermore, the shaft sleeve  40  includes seals  83 , which can be elastomeric, and can help seal the interface between the shaft sleeve  40  and adjacent components of the pump  20 . 
         [0081]      FIGS. 7A-7D  depict the seal sleeve  48  according to one embodiment of the present invention. The seal sleeve  48  is designed to substantially surround the shaft sleeve  40 , as shown in  FIG. 4 , and to rotate with the shaft sleeve  40  and the shaft  30 . To this end, torque is transferred to the seal sleeve  48  via set screws (not shown) that pass through apertures  84  in the wall of the seal sleeve  48 , and into engagement with the indents  82  of the shaft sleeve  40  (shown in  FIG. 6C ). 
         [0082]    The seal sleeve  48  also includes grooves  86  for accepting seals  88 . Seals  88  can be elastomeric, and can serve to seal the interface between the seal sleeve  48  and the shaft sleeve  40 , as well as the interface between the seal sleeve  48  and the rotating inboard seal carrier  52 . Another feature of the seal sleeve  48  is a flattened portion  90  on the outer surface of the seal sleeve  48 . This flattened portion  90  is designed to interact with, and transmit torque to, a corresponding flattened feature  91  on the inner surface of the rotating inboard seal carrier  52 . Yet another feature of the seal sleeve  48  is an indented portion  92  of its outer diameter. One purpose for this indented portion  92  is to ensure that, once the seal  32  is fully assembled, there is a gap  94  (shown in  FIG. 4 ) between the seal sleeve  48 , which rotates with the shaft  30 , and stationary components of the seal  32 , such as the spring holder  58  and the stationary seals and carriers. In addition, the seal sleeve  48  includes a snap ring groove  93  for receiving the snap ring  72  during assembly of the seal  32 . 
         [0083]      FIGS. 8A and 8B  show the rotating inboard seal carrier  52 , including the flattened feature  91  on its inner surface that engages the flattened portion  90  of the outer surface of the seal sleeve  48 . Via this flattened feature  91 , the seal sleeve  48  transfers torque to the rotating inboard seal carrier  52  so that it rotates along with the shaft  30 , shaft sleeve  40 , and seal sleeve  48 . The rotating inboard seal carrier  52  further includes an annular gripping protrusion  96  configured to accept the rotating inboard seal  50 . The rotating inboard seal  50  is shown in  FIGS. 8D and 8E . This seal can be made of tungsten, or any other appropriate material. In addition, an outer edge  98  of the rotating inboard seal  50  may be chamfered. 
         [0084]    Referring now to  FIGS. 9A-9C , there is shown the stationary inboard seal carrier  56 . Stationary inboard seal carrier  56  can include notches  100  around the inner surface thereof. One purpose of the notches  100  may be to accept corresponding protrusions on the spring holder  58  in order keep the stationary inboard seal carrier  56  stationary, and to prevent it from rotating relative to the spring holder  58 . The stationary inboard seal carrier  56  further includes an annular gripping protrusion  102  configured to accept the stationary inboard seal  54 . The stationary inboard seal  54  is shown in  FIGS. 9D and 9E . This seal can be made of tungsten, or any other appropriate material. In addition, an inner edge  104  of the stationary inboard seal  54  may be chamfered. When the seal  32  is fully assembled, the surface of the rotating inboard seal  50  and the surface of the stationary inboard seal  54  make up the inboard seal surfaces. 
         [0085]      FIGS. 10A-10D  depict the spring holder  58 . The spring holder  58  is an annular member that surrounds the seal sleeve  48 , and is attached to the gland plate  60 , discussed below. The outer surface of the spring holder  58  is stepped, as shown in  FIG. 10B , having a relatively smaller outer diameter along a first portion  103 , and relatively larger diameters along second portion  105 . As shown in  FIGS. 10A and 10C , the spring holder  58  also has a plurality of holes  106  arranged circumferentially around a top surface  108  that extend axially into the body of the spring holder  58 . These holes  106  each receive a spring  110  (shown in  FIG. 4 ). Upon assembly, the springs are compressed using a jig (not shown) and then held in place relative to the gland plate  60  using the snap ring  72 . The springs  110  to exert a force F (shown in  FIG. 4 ) in a direction toward the inboard seal, and this force F pushes the surface of the stationary inboard seal  54  against the surface of the rotating inboard seal  50  to create a face seal. In addition to the holes  106 , the spring holder  58  further includes a circumferential groove  112  for accepting an O-ring seal  114 , as shown in  FIG. 10D . The O-ring seal  114  serves to help seal the interface between the spring holder  58  and the gland plate  60 . In addition, the spring holder  58  includes notches  111  in the top surface  108  thereof. The purpose of the notches  111  is to accept fasteners (not shown) for attaching the spring holder  58  to the gland plate  60  so that the spring holder  58  does not rotate relative to the gland plate  60 . 
         [0086]    Referring to  FIGS. 11A-11E , there is shown the gland plate  60  according to an example embodiment of the invention. The gland plate  60  is designed to be fixedly attached to the frame  28  of the pump  20 . As shown in  FIGS. 11A and 11C , the gland plate  60  includes apertures  116  for receiving fasteners (not shown). As described above, the fasteners in the gland plate  60  extend inwardly through the gland plate  60  and engage the notches  111  in the spring holder  58  to prevent the spring holder  58  from rotating relative to the gland plate  60 . In addition, as shown in  FIGS. 11B and 11E , the gland plate includes an outer annular protrusion  118  and an inner annular protrusion  120 . The outer annular protrusion  118  extends away from the inboard seal, as shown in  FIG. 4 , and surrounds the outboard seal carrier  64 . The inner annular protrusion  120  extends toward the inboard seal, also as shown in  FIG. 4 , and surrounds a portion of the spring holder  58 . The gland plate further includes a circumferential recess  121  configured to accept an O-ring seal  123 . This O-ring seal can help seal the interface between the gland plate  60  and the spring holder  58 . 
         [0087]    Another feature of the gland plate, which is best shown in  FIGS. 11A and 11D , is a pair of coolant ports  122 . In practice, a coolant source can be connected to one of the coolant ports  122  to inject coolant through the coolant port  122 . The coolant source may be, for example, a barrier fluid tank mounted somewhere near the blender pump at a well site. The barrier fluid, or coolant, can be any fluid that is compatible with the pumped fluid. As coolant is supplied to the inside of the gland plate  60  through the coolant port  122 , is enters the gap  94  between the seal sleeve  48  and the stationary components of the seal  32 . The coolant can travel in the gap  94  until it reaches the inboard and outboard seal surfaces, which it can help to cool. The coolant channels heat away from the seal surfaces and exits via the alternate cooling port  122 . Although two cooling ports  122  are shown in the gland plate  60  of the embodiment of  FIGS. 11A-11E , any number of cooling ports can be used. The ability to cool the seal  32  via the cooling ports in the gland plate  60  is advantageous for a number of reasons. 
         [0088]    For example, in most known pumps used to pump heavy fluid slurries that are corrosive and abrasive, such as many fluids commonly used in hydraulic fracturing operations, the abrasive nature of the slurry leads to seal face combinations that have a very high coefficient of friction. At the same time, the faces of the seal are typically cooled by the fluid being pumped. As a result, if a fluid running into the pump stops, such as due to the fluid source running dry, the resultant lack of fluid at the seal surfaces can very quickly lead to heat spikes at the seal faces and failure of the seals. This problem can be compounded if an operator, realizing the problem, suddenly reintroduces fluid to the seal surfaces, thereby causing the seal faces to crack due to the large temperature differentials. This problem is often encountered in the field, for example, if an operator does not shut the blender down soon enough when the pump  20  is shut down. 
         [0089]    The cooling ports  122  in the gland plate  60  of the present invention alleviate this problem by providing a secondary coolant source. Thus, if pumping fluid stops cooling the seal surfaces, the coolant provided through the cooling ports  122  in the gland plate  60  can temporarily cool the seal surfaces and preserve the seal  32 . This cooling mechanism can therefore save time and money spent servicing or replacing ruined seals in the field. 
         [0090]      FIGS. 12A and 12B  show the snap ring  72  that can be used to hold the springs  110  in a compressed condition relative to the rotating seal  32  components, as discussed in greater detail below. The snap ring  72  is split, so that its diameter can be reduced during insertion.  FIGS. 13A and 13B  show a spacer  74  that can be inserted in the seal  32  assembly as needed to adjust the spacing between components. Both the snap ring  72  and the spacer  74  can be installed on the outboard side of the rotating outboard seal carrier  68 . 
         [0091]    Referring to  FIGS. 14A and 14B , there is shown the stationary outboard seal carrier  64 . Upon insertion into the assembly, the inboard side of the stationary outboard seal carrier  64  can contact the springs  110  in the spring holder  58 , so that when the stationary outboard seal carrier  64  is pushed in an inboard direction relative to the spring holder  58  and the gland plate  60 , the springs  110  are compressed. The stationary outboard seal carrier  64  is also circumscribed by a recess  125  configured to accept an O-ring  127 . The stationary outboard seal carrier  64  further includes an annular gripping protrusion  126  configured to accept the stationary outboard seal  62 . The stationary outboard seal  62  is shown in  FIGS. 14C and 14D . This seal can be made of carbon, or any other appropriate material. In addition, the stationary outboard seal  62  can be stepped. One purpose of the stepped profile of the stationary outboard seal  62  may be to increase the surface area of the seal  62 . 
         [0092]      FIGS. 15A and 15B  show the rotating outboard seal carrier  68 , including holes  128  for receiving fasteners to fasten the outboard seal carrier  68  to the drive collar  70 . Via these fasteners, the drive collar  70  transfers torque to the rotating outboard seal carrier  68  so that it rotates along with the shaft  30 , shaft sleeve  40 , seal sleeve  48 , and drive collar  70 . The rotating outboard seal carrier  68  further includes an annular gripping protrusion  130  configured to accept the rotating outboard seal  66 . The rotating outboard seal  66  is shown in  FIGS. 15C and 15D . This seal can be made of tungsten, or any other appropriate material. In addition, an outer edge  132  of the rotating outboard seal  66  may be chamfered. When the seal  32  is fully assembled, the surface of the rotating outboard seal  66  and the surface of the stationary outboard seal  62  make up the outboard seal surfaces. 
         [0093]    Referring back to  FIGS. 12A and 12B , which show the snap ring  72  and spacer  74 . The spacer can be installed in the assembly on the outboard side of the rotating outboard seal carrier. Then, the spacer ring can be installed on the outboard side of the snap ring  72 , followed by the drive collar  70 , as discussed below. 
         [0094]    Referring now to  FIGS. 16A-16C , there is shown a drive collar  70  according to an embodiment of the present invention. The drive collar  70  includes axial apertures  134  around the circumference thereof to accept fasteners that may be used to fasten the drive collar  70  to the rotating outboard seal  66 . The fasteners may be any type of appropriate fastener, including threaded or unthreaded fasteners. The drive collar  70  also includes radial apertures  136  to accept fasteners that may be used to fasten the drive collar  70  to the seal sleeve  48 , thereby allowing the seal sleeve  48  to transmit torque to the drive collar  70 . The drive collar  70  is circumscribed by a recess  138  that accepts an O-ring seal  140 . One purpose of the O-ring seal is to seal the interface between the drive collar  70  and other components of the pump  20 . 
         [0095]    Assembly of the seal can be accomplished by the following method. The rotating inboard seal  50  and carrier  52  is placed over the seal sleeve  48 . The stationary inboard seal  54  and carrier  56  is then placed over the seal sleeve  48  so that the stationary inboard seal  54  faces the rotating inboard seal. Next, the spring holder  58  can be attached to the gland plate  60 , and both components can be placed over the seal sleeve  48  until the spring holder  58  engages the stacked inboard seal carriers  52 ,  56 . The springs  110  can then be installed in the spring holder  58 , followed by the stationary outboard seal  62  and carrier  64  and the rotating outboard seal  66  and carrier  68 , respectively. Next, the spacer  74  can be installed, followed by the snap ring  72 . The springs  110  can be compressed using a jig, which pushes the snap ring  72  inwardly in an inboard direction until the snap ring  72  engages the snap ring groove  93  in the seal sleeve  48 . Finally, the drive collar  70  can be placed over the seal sleeve  48 . 
         [0096]    Referring back to  FIG. 4 , it can therefore be seen that rotating components of the seal  32  (e.g., the shaft sleeve  40 , seal sleeve  48 , rotating inboard seal  50  and carrier  52 , rotating outboard seal  66  and carrier  68 , and drive collar  70 ) are free to rotate relative to the stationary components of the seal  32  (e.g., the stationary inboard seal  54  and carrier  56 , spring holder  58 , gland plate  60 , and stationary outboard seal  62  and carrier  64 ). Furthermore, each of the stationary components of the seal  32  can move axially relative to the gland plate  60  a predetermined distance. This distance is controlled by the pin  76 , which attaches to the gland plate  60  at a first pin end  142 , and steps inward toward the spring holder  105  at a second pin end  144 . In the embodiment shown in  FIG. 4 , the diameter of the pin  76  at the second pin end  144  is similar to the diameter of the outer surface of the first portion  103  of the spring holder  58 . 
         [0097]    Thus positioned, the pin  76  limits the movement of the stationary components of the seal  32  relative to the gland plate. Specifically, the seal  32  is limited in its movement away from the pump housing  22  by the stationary inboard seal carrier  156  because if moved far enough, the stationary inboard seal carrier  156  will contact the second pin end  144 , which will prohibit further movement in that direction. Similarly, the seal  32  is limited in its movement toward the pump housing  22  by the second portion  105  of the spring holder  58  because if moved far enough, the second portion  105  of the spring holder  58  will contact the second pin end  144 , which will prohibit further movement in that direction. 
         [0098]    Even with its movement limited as herein described, however, the seal  32  is able to move a distance D between the farthest limits of its motion toward and away from the seal housing  22 . In some embodiments, the distance D can be up to 0.25 inch or more. Throughout such movement, the inboard seal surface maintain sealed engagement, due to the force F exerted by the springs  110  in the spring holder  58 . Thus, fluids do not leak from the seal during adjustment of the seal. It is this freedom of movement, without breaking the inboard or outboard seals, that allows adjustment of the shaft  30  and seal  32  to accommodate wear of the impeller  38 , as discussed above. 
         [0099]    While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.