Abstract:
A multi-diameter bellows for use in a seal section of a submersible pump. The bellows is adapted to surround a shaft that communicates the motor with the pump. The bellows is made of a first collapsible section and a second collapsible section. The volume of the bellows is varied by moving a coupling member that attaches the first collapsible section to the second collapsible section. The coupling member has an outside portion for connecting to the second collapsible section and an inside portion for connecting to the first collapsible section. The coupling member additionally has a transitional section between the outside portion and the inside portion. The transitional portion of the coupling member allows the inside portion to be located within the second collapsible section, i.e., allows the collapsible sections to be “nested”, which increases displaced volume for a given stroke length of the coupling member.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation-in-part of U.S. patent application Ser. No. 10/350,788, filed on Jan. 23, 2003, and incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to a seal section for an electrical submersible pump. More particularly, the invention relates to a bellows in a seal section of an electrical submersible pump. 
   2. Background 
   Electrical submersible pumps (ESPs) have been used to lift fluid from bore holes, particularly for oil production. In operation, a pump of an electrical submersible pump is placed below the fluid level in the bore hole. The well fluid often contains corrosive compounds such as brine water, CO 2 , and H 2 S that can shorten the run life of an ESP when the ESP is submerged in the well fluid. Corrosion resistant units have been developed that have motors that utilize seals and barriers to exclude the corrosive agents from the internal mechanisms of the ESP. 
   A typical submersible pump has a motor, a pump above the motor, and a seal section between the motor and the pump. The seal section allows for expansion of the dielectric oil contained in the rotor gap of the motor. Temperature gradients resulting from an ambient and motor temperature rise cause the dielectric oil to expand. The expansion of the oil is accommodated by the seal section. Additionally, the seal section is provided to equalize the casing annulus pressure with the internal dielectric motor fluid. The equalization of pressure across the motor helps keep well fluid from leaking past sealed joints in the motor. It is important to keep well fluids away from the motor because well fluid that gets into the motor will cause early dielectric failure. Measures commonly employed to prevent well fluids from getting into the motor include the use of elastomeric bladders as well as labyrinth style chambers to isolate the well fluid from the clean dielectric motor fluid. Multiple mechanical shaft seals keep the well fluid from leaking down the shaft. The elastomeric bladder provides a positive barrier to the well fluid. The labyrinth chambers provide fluid separation based on the difference in densities between well fluid and motor oil. Any well fluid that gets past the upper shaft seals or the top chamber is contained in the lower labyrinth chambers as a secondary protection means. 
   One problem with the use of an elastomeric bladder is that, in high temperature applications, elastomeric bladders may experience a short usable life or may not be suitable for use. Elastomeric materials having a higher temperature tolerance tend to be very expensive. An alternative is to replace the elastomeric bladder with a bellows made of metal or another material that may expand as necessary, but which is suitable for use in high temperature applications, and/or which provide improved reliability over an elastomeric bladder. 
   Bellows have been used previously in submersible pump applications and other pumping systems. For example, the use of bellows is taught in U.S. Pat. Nos. 2,423,436, 6,059,539, and 6,242,829. Previous use of bellows in an ESP has required that the bellows be placed in an awkward configuration, e.g., as taught in U.S. Pat. No. 2,423,436, or that the bellows be located below the motor in an ESP to avoid interfering with a shaft that traverses the length of the ESP to deliver power from the motor to the pump. 
   It is desirable to be able to use a bellows to replace an elastomeric expansion bag, and that the bellows be configured in a similar manner to the more commonly used elastomeric expansion bag. 
   SUMMARY OF THE INVENTION 
   According to the present invention there is provided an improvement in a positive barrier to well fluid in a submersible pump, wherein the barrier is suitable for high temperature applications. 
   A multi-diameter bellows provides a positive barrier to well fluids. The multi-diameter bellows is preferably located in a seal section to assist in allowing expansion of the dielectric oil, to equalize the casing annulus pressure with the internal dielectric motor fluid and to isolate the well fluid from the clean dielectric motor fluid. The multi-diameter bellows of the invention may be made from materials that are less expensive and are suitable for higher temperatures than an elastomeric bag. 
   The multi-diameter bellows of the invention is preferably located in a bellows chamber of a seal section of an electrical submersible pump, wherein the seal section is located between a pump and a motor. The bellows chamber has a first end and a second end. A shaft communicates the motor with the pump, and runs through the bellows chamber in the seal section. The bellows is located in the bellows chamber and surrounds the shaft. The bellows is made of a first collapsible section and a second collapsible section. The first collapsible section communicates with the first end of the bellows chamber. The first collapsible section has a first cross-sectional area, e.g., a relatively large diameter. The second collapsible section communicates with the second end of the bellows chamber. The second collapsible section has a second cross-sectional area, e.g., a relatively small diameter. A first coupling member, e.g., a coupling ring, is provided between the first collapsible section and the second collapsible section and also surrounds said shaft. A volume within the bellows is varied by movement of the first coupling member towards either of the first end and the second end. 
   In a second embodiment of the bellows of the invention, a large diameter section is attached to the bellows chamber at a first end. A second end of the large diameter section has a coupling member thereon, which transitions the bellows from the first large diameter section to a small diameter section. On the other end of the small diameter section, a second coupling member is provided to transition the small diameter section to a second large diameter section, which is affixed to the other end of the bellows chamber. In both embodiments, the ends of the bellows are fixed. The volume within the bellows is varied by movement of the coupling member or coupling members. For example, to increase the volume of the bellows, the coupling member or coupling members are displaced to minimize the volume of the small diameter section and to maximize the volume of the large diameter sections. Conversely, to decrease the volume of the bellows, the coupling members are displaced to maximize the volume of the small diameter section and to minimize the volume of the large diameter section. One advantage of the second bellows embodiment is that the bellows is still partially functional even if one of the coupling members becomes stuck, thereby increasing reliability of the seal section. 
   In another embodiment of the invention, a coupling member may be utilized that is adapted to facilitate a nested bellows. For example, a coupling member may be provided with an outside portion for engaging an end surface of a large diameter bellows. A transitional portion of the coupling member preferably extends inside of the large diameter bellows. An inside portion of the coupling member may be provided for affixing to an end surface of a small diameter bellows. Preferably, the transitional portion of the coupling member extends within the large diameter bellows so that the inside portion of the coupling member is located within the large diameter bellows. Therefore, the outside portion of the coupling member lies in a different plane than the inside portion of the coupling member, since the outside portion and inside portion are spaced apart by the transitional portion. As a result, a portion of the small diameter bellows extends within a portion of the large diameter bellows, i.e., is “nested” therein. A result of nesting the bellows is that for a given length of a bellows chamber, volume displaced by a multi-diameter bellows may be increased. 
   A better understanding of the present invention, its several aspects, and its advantages will become apparent to those skilled in the art from the following detailed description, taken in conjunction with the attached drawings, wherein there is shown and described the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated for carrying out the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a cross-sectional view of a lower section seal section for an electrical submersible pump having a first embodiment of a multi-diameter metal bellows. 
       FIG. 1B  is a cross-sectional view of an upper section of a seal section for an electrical submersible pump having a second embodiment of multi-diameter metal bellows. 
       FIG. 2A  is a schematic diagram of the first embodiment of the multi-diameter bellows of  FIG. 1A  shown in a neutral position. 
       FIG. 2B  is a schematic diagram of the first embodiment of the multi-diameter bellows shown in  FIG. 1A  shown in a fully collapsed or minimum volume configuration. 
       FIG. 2C  is a schematic diagram of the first embodiment of the metal bellows of  FIG. 1A  shown in a completely expanded or maximum volume configuration. 
       FIG. 3A  is a schematic diagram of the second embodiment of the multi-diameter bellows shown in  FIG. 1B  shown in a neutral position. 
       FIG. 3B  is a schematic diagram of the second embodiment of the multi-diameter bellows shown in  FIG. 1B  shown in a fully retracted or minimum volume configuration. 
       FIG. 3C  is a schematic diagram of the second embodiment of the multi-diameter bellows shown in  FIG. 1B  shown in a fully expanded or maximum volume configuration. 
       FIG. 4A  is a schematic diagram of the first embodiment of a nested multi-diameter bellows shown in a neutral position. 
       FIG. 4B  is a schematic diagram of the first embodiment of the nested multi-diameter bellows shown in a fully collapsed or minimum volume configuration. 
       FIG. 4C  is a schematic diagram of the first embodiment of the nested multi-diameter bellows shown in an expanded or maximum volume configuration. 
       FIG. 5A  is a schematic diagram of a second embodiment of a nested multi-diameter bellows shown in a neutral position. 
       FIG. 5B  is a schematic diagram of a second embodiment of a nested multi-diameter bellows shown in a fully retracted or minimum volume configuration. 
       FIG. 5C  is a schematic diagram of a second embodiment of a nested multi-diameter bellows shown in a fully expanded or maximum volume configuration. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Before explaining the present invention in detail, it is important to understand that the invention is not limited in its application to the details of the embodiments and steps described herein. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation. 
   Referring now to  FIGS. 1A and 1B , shown is a typical submersible pump configuration wherein a seal section  10  is located between a pump section  12  and a motor section  14 . Seal section  10  is made up of a lower seal section  16  ( FIG. 1A ) and an upper seal section  18  ( FIG. 1B ). Referring now in particular to  FIG. 1A , lower seal section  16  has a housing  20 . A base  22  is located in a lower end of a housing  20 . Base  22  defines a sleeve receptacle  24 . A lower shaft  26  is located within housing  20 . A first sleeve  28  surrounds lower shaft  26  and is located in sleeve receptacle  24  of base  22 . Lower sleeve block  30  is at least partially located within housing  20 . Lower sleeve block  30  defines a sleeve receptacle  32  on a lower end and a collar receptacle  34  on an upper end. A second sleeve  36  is located within the sleeve receptacle  32  of lower sleeve block  30 . 
   A lower guide tube collar  38  is located within collar receptacle  34  of lower sleeve block  30 . A lower head  40  is at least partially located within housing  20  and is located above lower sleeve block  30 . Lower head  40 , housing  20  and lower sleeve block  30  define a lower bellows chamber  42 . Lower head  40  defines a ring receptacle  44  on a lower end and a sleeve receptacle  46  above ring receptacle  44 . Lower head  40  also defines a lower shaft seal receptacle  48  on an upper end. Fluid bypass conduit  50  and fluid passageway  52  are also defined by the lower head  40 . Fluid passageway  52  communicates with an annular space that surrounds lower shaft  26  and also with lower bellows chamber  42 . A check valve  54  is provided in fluid passageway  52  to prevent fluid from passing from the lower bellows chamber  42  back into fluid passageway  52 . 
   A guide tube ring  56  is located within ring receptacle  44 . A ring retainer collar  58  is threadably received on a guide tube ring  56 . Ring retainer collar  58  is preferably provided with a ridge  60  for engaging an inside surface of housing  20 . A lower guide tube  64  is located inside lower bellows chamber  42 . Lower guide tube  64  is attached at a first end to the guide tube ring  56  and at a second end to lower guide tube collar  38  and surrounds lower shaft  26 . Lower guide tube  64  is preferably provided with orifices  66  proximate an upper end up the lower guide tube  64 . A first embodiment of a multi-diameter bellows  68  surrounds lower guide tube  64 . Multi-diameter bellows  68  has a small diameter portion  70  and a large diameter portion  72 . Bellows  68  may be made of metal or other high temperature resistant materials or other suitable materials as desired. 
   Referring now to  FIGS. 2A-2C , the multi-diameter bellows  68  can be seen in greater detail. Small diameter portion  70  has an upper end  74  affixed to ring retainer collar  58 . Large diameter portion  72  has a lower end  76  affixed to lower guide tube collar  38 . Small diameter portion  70  is separated from large diameter portion  72  by a coupling ring  78 . Coupling ring  78  is attached to an upper end of large diameter portion  72  and to lower end of small diameter portion  70 . Coupling ring  78  is preferably provided with a runner  80  for slidably engaging the lower guide tube  64 . Multi-diameter bellows  68  is also preferably provided with at least one stabilizer disk  82  that is also provided with a runner  84  on an inner diameter of the stabilizer disk  82  for slidably engaging lower guide tube  64 . Stabilizer disk  82  also communicates with an outer diameter of large diameter portion  72 . Stabilizer disk  82  preferably has a first side attached to a segment of a large diameter portion  70  and has a second side attached to a separate segment of large diameter portion  72 . Stabilizer disk  82  is preferably provided with orifices  83  formed therein for permitting fluid to pass therethrough within the multi-diameter bellows  68 . 
   Referring back to  FIG. 1A , a third sleeve  86  is located in the sleeve receptacle  46  of lower head  40 . A lower shaft seal  88  is located partially in the lower shaft seal receptacle  48  of lower head  40 . Lower shaft seal  88  is provided to prevent fluid migration along lower shaft  26 . A coupling  90  is provided on an upper end of lower shaft  26 . 
   Referring now to  FIG. 1B , upper seal section  18  has an upper base  100  affixed to an upper end of lower head  40 . An upper housing  102  has a lower end has is affixed to upper base  100 . Upper base  100  has a sleeve receptacle  101  formed in an upper end. An upper shaft  104  passes through upper housing  102 . Upper shaft  104  has a lower end that engages coupling  90 . A fourth sleeve  105  is located in sleeve receptacle  101 . Upper sleeve block  106  is at least partially located within upper housing  102 . Upper sleeve block  106  defines a sleeve receptacle  108  at a lower end thereof and a collar receptacle  110  on an upper end. A fifth sleeve  112  is located within sleeve receptacle  108 . A lower guide tube collar  114  is located within collar receptacle  110 . Upper head  116  is at least partially located within upper housing  102  and above upper sleeve block  106 . The upper head  116 , the upper housing  102  and the upper sleeve block  106  define an upper bellows chamber  118 . The upper head  116  defines a ring receptacle  120  on a lower end and a sleeve receptacle  122  above ring receptacle  120 . Additionally, upper head  116  defines an upper shaft seal receptacle  124  on an upper end. Upper head  116  additionally defines a fluid passageway  126  that communicates an annular space around upper shaft  104  with the upper bellows chamber  118 . A check valve  128  is provided for allowing fluid to pass from fluid passageway  126  to the upper bellows chamber  118 . The portion of upper housing  102  that defines the upper bellows chamber  118  is provided with perforations  130  to allow well fluids to migrate into the upper bellows chamber  118  to equalize pressure between the upper bellows chamber  118  and the wellbore. 
   An upper guide tube ring  132  is located within ring receptacle  120 . An upper guide tube  138  is attached to the lower guide tube collar  114  on a lower end and is attached to the upper guide tube ring  132  at an upper end. A second embodiment of a multi-diameter bellows  140  surrounds the upper guide tube  138 . Multi-diameter bellows  140  has a first large diameter portion  142 , a second large diameter portion  144 , and a small diameter portion  146 . Bellows  140  may be made of metal or other high temperature resistant materials or other suitable materials as desired. 
   Referring now to  FIGS. 3A-3C , multi-diameter bellows  140  is shown in greater detail. An upper end  148  of the multi-diameter bellows  140  is affixed to the upper guide tube ring  132 . A lower end  150  of the multi-diameter bellows  140  is affixed to the lower guide tube collar  114 . Small diameter portion  146  is located between first large diameter portion  142  and second large diameter portion  144 . A first end of the small diameter portion  146  engages the first large diameter portion  142  and is attached to a first coupling ring  152 . First coupling ring  152  is attached to an upper end of the small diameter portion  146  and to a lower end of the first large diameter portion  142 . The first coupling ring  152  preferably has a runner  154  located thereon for slidably engaging upper guide tube  138 . A second end of the small diameter portion  146  is attached to the second large diameter portion  144  by a second coupling ring  156 . Second coupling ring  156  is attached to a lower end of the small diameter portion  146  and to an upper end of second large diameter portion  144 . Second coupling ring  156  is also preferably provided with a runner  158  for engaging the upper guide tube  138 . 
   Multi-diameter bellows  140  also is preferably provided with a plurality of stabilizer disks  160  that have runners  162  provided on an inner diameter of the stabilizer disks  160  for slidably engaging upper guide tube  138 . The stabilizer disks  160  communicate with an outer diameter of the first large diameter portion  142  and with an outer diameter of second large diameter portion  144 . The stabilizer disks  160  preferably have a first side attached to a first segment of the first or second large diameter portions  142 ,  144  and a second side attached to a second segment of the first or second large diameter portions  142 ,  144 . Stabilizer disks  160  are preferably provided with orifices  161  formed therein for permitting fluid to pass through the stabilizer disks  160  within the multi-diameter bellows  140 . 
   Referring back to  FIG. 1B , a sixth sleeve  164  is located in sleeve receptacle  122  of the upper head  116 . An upper shaft seal  166  is located partially in the upper shaft seal receptacle  124  of the upper head  116 . The upper shaft seal  166  is provided to prevent fluid migration along the upper shaft  104 . 
   Referring now to  FIGS. 4A-4C , a multi-diameter nested bellows  268  is shown. Small diameter portion  270  has an upper end  274  for affixing to a retainer such as collar  58  ( FIG. 1A ). Large diameter bellows portion  272  has a lower end  276  affixed to a retainer such as lower guide tube collar  38  ( FIG. 1A ). Small diameter bellows portion  270  is separated from large diameter bellows portion  272  by a coupling ring  278 . Coupling ring  278  is attached to an upper end of large diameter bellows portion  272  and to lower end of small diameter bellows portion  270 . Coupling ring  278  has an outside portion  278   a , an inside portion  278   b  and a transitional portion  278   c.    
   Referring now to  FIGS. 5A-5C , a second embodiment of multi-diameter bellows  340  is shown. An upper end  348  of the multi-diameter bellows  340  may be affixed to a retainer such as upper guide tube ring  32  ( FIG. 1B ). A lower end  350  of the multi-diameter bellows  340  may be affixed to a lower guide tube collar, such as collar  114  ( FIG. 1B ). Small diameter bellows portion  346  is located between first large diameter bellows portion  342  and second large diameter bellows portion  344 . A first end of small diameter bellows portion  346  engages a first coupling ring  352  that is in communication with first large diameter bellows portion  342 . First coupling ring  352  is attached to an upper end of the small diameter bellows portion  346  and to a lower end of the first large diameter bellows portion  342 . The first coupling ring  352  has an outside portion  352   a , an inside portion  352   b , and a transitional portion  352   c . A second end of the small diameter bellows portion  346  is attached to second large diameter bellows portion  344  by a second coupling ring  356 . Second coupling ring  356  is attached to a lower end of the small diameter bellows portion  346  and to an upper end of second large diameter bellows portion  344 . Second coupling ring  356  has an outside portion  356   a , an inside portion  356   b , and a transitional portion  356   c.    
   In practice, dielectric fluid surrounding motor  14  is heated by operation of motor  14  and/or by conducting heat from the well environment. As a result, the dielectric fluid expands and migrates through base  22  past first sleeve  28  and up lower shaft  26 . The dielectric fluid may continue to migrate past second sleeve  36 , through lower sleeve block  30  and into the annular space between the lower shaft  26  and the lower guide tube  64 . Once dielectric fluid migrates into lower guide tube  64 , the dielectric fluid passes through orifices  66  in lower guide tube  64  and into the small diameter portion  70  of the multi-diameter bellows  68 . The dielectric fluid may then fill the small diameter portion  70  and large diameter portion  72  of the multi-diameter bellows  68 . 
   Once the volume within the multi-diameter bellows  68  is full of fluid, then coupling ring  78  will propagate along lower guide tube  64  to increase the volume within the large diameter portion  72  until such time as the small diameter portion  70  is fully compressed. When the small diameter portion  70  is fully compressed, then the multi-diameter bellows  68  is at full capacity. Once the multi-diameter bellows  68  is at full capacity, the dielectric fluid will migrate through fluid passageway  52  in lower head  40  and out through check valve  54  into the lower bellows chamber  42 . Once lower bellows chamber  42  becomes full, the fluid may continue to migrate upwardly through fluid bypass conduit  50 , which allows the fluid to bypass lower shaft seal  88 . 
   If necessary, the dielectric fluid will continue to migrate upwardly in the seal section  10  past coupling  90  and into the upper seal section  18  where fluid will migrate through upper base  100  past fourth sleeve  105  and through the annular space surrounding the upper shaft  104 , and through fifth sleeve  112  in upper sleeve block  106 . Dielectric fluid will then continue to migrate up through the annular space between the upper shaft  104  and the upper guide tube  138  where the fluid migrates out of upper guide tube  138  and into the multi-diameter bellows  140 . 
   The dielectric fluid fills first large diameter portion  142 , small diameter portion  146 , and second large diameter portion  144  of multi-diameter bellows  140 . Once the internal volume of the multi-diameter bellows  140  is completely full of fluid, first coupling ring  152  and second coupling ring  156  propagate along upper guide tube  138  toward one another, thereby expanding the volume of the first large diameter portion  142  and second large diameter portion  144  while compressing small diameter portion  146 . As more fluid is added to the multi-diameter bellows  140 , the first large diameter portion  142  and second large diameter portion  144  will continue to expand until small diameter portion  146  is fully compressed as shown in  FIG. 3C , which illustrates the maximum volume configuration of multi-diameter bellows  140 . Dielectric fluid will then migrate up through fluid passageway  126  and out through check valve  128  where the dielectric fluid will co-mingle with well fluids that are able to enter through perforations  130  in upper housing  102 . Therefore, the pressure within the multi-diameter bellows  140  will be maintained in equilibrium with wellbore pressure. 
   In the case of nested bellows  268  ( FIGS. 4A-4C ), once dielectric fluid passes into the small diameter bellows portion  270  of the multi-diameter bellows  268 , the dielectric fluid may fill the small diameter bellows portion  270  and large diameter bellows portion  272  of the multi-diameter bellows  268 . 
   As the volume within the multi-diameter bellows  268  fills with fluid, coupling member  278  will propagate along lower guide tube  64  to increase the volume within the large diameter bellows portion  272  until such time as the small diameter bellows portion  270  is fully compressed or until such time as outer portion  278   a  of coupling ring  278  makes contact with a retainer as shown in  FIG. 4C . 
   In a preferred embodiment, outer portion  278   a  of coupling ring  278  functions as a stop against the retainer ( FIG. 4C ) to prevent over-compression of small diameter portion  270  or over-extension of large diameter portion  272 , thereby avoiding the infliction of potentially damaging stress upon portions  270 ,  272 . During operation, when small diameter portion  270  is fully compressed, the multi-diameter bellows  268  is at full capacity. Once the multi-diameter bellows  268  is at full capacity, the dielectric fluid will migrate out of bellows  268  through a fluid passageway. 
   Conversely, when nested bellows  268  is in a fully contracted or minimum volume configuration, as shown in  FIG. 4B , large diameter bellows portion  272  is fully compressed and small diameter bellows portion  270  is fully expanded. In a preferred embodiment, inner portion  278   b  makes contact with a retainer and functions as a stop to prevent over expansion of small diameter bellows portion  270  or over compression of large diameter bellows portion  272 . 
   With respect to the second embodiment of multi-diameter nested bellows  340  ( FIGS. 5A-5C ), dielectric fluid fills first large diameter bellows portion  342 , small diameter bellows portion  346 , and second large diameter bellows portion  344  of multi-diameter nested bellows  340 . As the internal volume of the multi-diameter nested bellows  340  fills with fluid, first coupling member  352  and second coupling member  356  propagate along a guide tube, such as upper guide tube  38  ( FIG. 1B ) toward one another, thereby expanding the volume of first large diameter bellows portion  342  and second large diameter bellows portion  344  while compressing small diameter bellows portion  346 . 
   As more fluid is added to the multi-diameter bellows  340 , the first large diameter bellows portion  342  and second large diameter bellows portion  344  will continue to expand until small diameter bellows portion  346  is fully compressed or until outer portion  352   a  of first coupling member  352  and outer portion  356   a  of second coupling member  356  make contact, as shown in  FIG. 5C .  FIG. 5C  illustrates the maximum volume configuration of multi-diameter bellows  340 . When outer portions  352   a  and  356   a  are allowed make contact, outer portions  352   a  and  356   a  function as a stop to prevent over-expansion of first large diameter portion  342  and second large diameter portion  344  as well as over-compression of small diameter portion  344 . Once first large diameter portion  342  and second large diameter portion  344  are completely expanded, then dielectric fluid will migrate up through a fluid passageway. 
   To minimize volume of bellows  340 , small diameter bellows portion  346  is fully expanded while first large diameter bellows portion  342  and second large diameter bellows portion  344  are fully compressed, as shown in  FIG. 5B . 
   In a preferred embodiment, inner portions  352   b  of first coupling member  352  will make contact with a stop, as shown in  FIG. 5B , such as sleeve receptacle  32  ( FIG. 1B ). Similarly, as shown in  FIG. 5B , inner portion  356   b  of second coupling member  356  will make contact with a stop, such as lower guide tube collar  114  ( FIG. 1B ). When inner portions  352   b  and  356   b  are allowed to bump against their respective stops, inner portions  352   b  and  356   b  function to prevent over-expansion of small diameter bellows portion  346  as well as over-compression first large diameter bellows portion  342  and second large diameter bellows portion  344 . 
   Multiple embodiments of multi-diameter bellows are shown, i.e. multi-diameter bellows  68 ,  140 ,  268  and  340 . The example bellows are shown located in a seal section  10  having a lower section  16  and an upper section  18 . However, it should be understood that any of the multi-diameter bellows may be used in a seal section  10  having only a single section. Additionally, the multi-diameter bellows may be used in a seal section  10  having three or more sections as desired. Although seal section  10  is shown for purposes of example having both a first embodiment  68  and a second embodiment  140 , the seal section  10  could be used with two or more of the first embodiments  68  or second embodiments  140 , or embodiments  268  and  340  in any desired combination. 
   One advantage of the multi-diameter bellows is that the upper ends and lower ends are fixed. Therefore, the multi-diameter bellows occupy the same linear space of the seal section regardless of the volume of fluid located therein. The volume of the multi-diameter bellows is varied by movement of the coupling rings. 
   An additional advantage of the end mounted multi-diameter bellows is that the bellows surround the shafts. As a result, the multi-diameter bellows  68 ,  140  may be used above pump motor  14  in the same manner as elastomeric bags have been used previously. 
   While the invention has been described with a certain degree of particularity, it is understood that the invention is not limited to the embodiment(s) set for herein for purposes of exemplification but is to be limited only by the scope of the attached claim or claims including the full range of equivalency to which each element thereof is entitled.