Patent Publication Number: US-8967948-B2

Title: Uniaxial eccentric screw pump

Description:
FIELD OF THE INVENTION 
     The present invention relates to a uniaxial eccentric screw pump including a stator capable of being divided into an outer cylinder portion and a lining portion. 
     BACKGROUND OF THE INVENTION 
     Conventionally, prior art systems such as JP 2005-344587 A provide a pump called a uniaxial eccentric screw pump having structure in which a rotor formed into an external thread shape is inserted in an inside of a stator having an inner peripheral surface formed into an internal thread shape. Many stators adopted in the pump have structure in which a lining member made of rubber, a resin, or the like is inserted in an inside of a metal outer cylinder. In the stators adopted in a prior art systems, the outer cylinder and the lining member are fixed to each other through bonding or the like, which prevents positional shifts of the outer cylinder and the lining member and the positional shift of the lining member. 
     SUMMARY OF THE INVENTION 
     In recent years, consideration for environmental issues is required, and also the uniaxial eccentric screw pump is expected to have structure enabling the outer cylinder and the lining member constituting the above-mentioned stator to be easily separated and recovered. However, in a case where the outer cylinder and the lining member are fixed to each other through bonding as in the conventional technology, there is a problem in that considerable time and effort are required in order to separate the outer cylinder and the lining member from each other. Meanwhile, when adopting, in consideration of time and effort for separating and recovering, a configuration in which the outer cylinder is mounted simply in a non-bonded state on the lining member, there arises a problem such as the positional shift of the lining member in an axial direction and in a peripheral direction or deformation thereof, and hence there may be a variety of fears involving stabilizing an operation state of the uniaxial eccentric screw pump. Specifically, due to expansion and shrinkage of the lining member in the axial direction, a diameter of a through-hole formed in an inside of the lining member varies from part to part, and hence there may arise a problem such as an occurrence of uneven wear, or an unstable discharge amount. 
     Therefore, it is an object of the present invention to provide a uniaxial eccentric screw pump enabling a stator to be easily separated into an outer cylinder and a lining member, and being capable of solving problems such as a positional shift and deformation of the lining member, and an occurrence of uneven wear and an unstable discharge amount associated with the positional shift and deformation. 
     In order to solve the above-mentioned problems, according to an exemplary embodiment of the present invention, there is provided a uniaxial eccentric screw pump, including: a rotor of an external thread type; and a stator enabling the rotor to be inserted therethrough, the stator including: a liner portion having a cylindrical shape and being integrally formed so as to have an inner peripheral surface of an internal thread type; and an outer cylinder portion mounted in a pressed state on an outer periphery of the liner portion. In the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention, the liner portion includes, at both end portions thereof, collar portions protruding radially outward. Further, the outer cylinder portion is arranged between the collar portions, and end portions of the outer cylinder portion abut on the collar portions, respectively. 
     In the stator adopted in the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention, the outer cylinder portion is mounted in the pressed state on the liner portion, and hence the liner portion and the outer cylinder portion are integrated with each other without using an adhesive. Therefore, the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention enables the stator to be easily separated into the liner portion and the outer cylinder portion, and enables the stator to be recovered and recycled. 
     The uniaxial eccentric screw pump according to the exemplary embodiment of the present invention has the structure in which the outer cylinder portion is arranged between the collar portions provided at both the end portions of the liner portion, respectively, and in which the end portions of the outer cylinder portion abut on the collar portions, respectively. Therefore, the outer cylinder portion functions as a support for preventing the liner portion from shrinking in an axial direction, which can keep an inner diameter of the liner portion substantially uniform. Thus, it is possible to avoid uneven wear of the liner portion, and to stabilize a discharge amount. 
     According to an exemplary embodiment of the present invention, there is also provided a uniaxial eccentric screw pump, including: a rotor of an external thread type; and a stator enabling the rotor to be inserted there through, the stator including: a liner portion having a cylindrical shape and being integrally formed so as to have an inner peripheral surface of an internal thread type; and an outer cylinder portion mounted in a non-bonded state on the liner portion to cover an outer periphery of the liner portion. In the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention, the liner portion includes, at both end portions thereof, collar portions protruding radially outward. Further, the outer cylinder portion is arranged between the collar portions, and end portions of the outer cylinder portion abut on the collar portions, respectively. 
     In the stator adopted in the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention, the outer cylinder portion is mounted in the non-bonded state on the liner portion, and hence it is possible to easily separate and recover the outer cylinder portion and the liner portion. Further, the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention has the structure in which the outer cylinder portion is arranged between the collar portions provided at both the end portions of the liner portion, respectively, and in which the end portions of the outer cylinder portion abut on the collar portions, respectively, and thus can prevent the liner portion from shrinking in the axial direction. This can keep the inner diameter of the liner portion substantially uniform at any part. Thus, it is possible to avoid the uneven wear of the liner portion, and to stabilize the discharge amount. 
     In the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention, it is preferred that the outer cylinder portion is capable of being divided into a plurality of outer cylinder components in a peripheral direction thereof. 
     With this configuration, it is possible to more easily perform work of mounting/dismounting the outer cylinder portion to/from the liner portion. Note that, in a case where the outer cylinder portion is formed of the plurality of outer cylinder components, integrating the outer cylinder components with each other through clamp joining enables the work of mounting/dismounting the outer cylinder portion to be even more easily performed. 
     The above-mentioned uniaxial eccentric screw pump according to the exemplary embodiment of the present invention may further include an end stud arranged on one end side of the stator. The end stud and an end portion of a pump casing connecting to another end side of the stator are coupled and fastened by a screw rod so that the stator is integrally coupled to the pump casing together with the end stud. The end portions of the outer cylinder portion abut on the end stud and the end portion of the pump casing, respectively. 
     In a case of adopting this configuration, a fastening force (sandwiching force), which acts between the end stud and the pump casing through coupling and fastening by the screw rod, acts more preferentially on the outer cylinder portion than on the liner portion, and hence it is possible to prevent the liner portion from being compressed by the fastening force in the axial direction. Thus, the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention can further keep the inner diameter of the liner portion substantially uniform at any part. Therefore, according to the exemplary embodiment of the present invention, it is possible to avoid the uneven wear of the liner portion, and to stabilize the discharge amount. 
     Further, the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention is preferred to further include a fitting portion enabling at least one of the collar portions to be fitted thereto, the fitting portion being provided at the end stud and/or the end portion of the pump casing. It is preferred that, at the fitting portion, the at least one of the collar portions is sandwiched between the end stud and the outer cylinder portion and/or between the pump casing and the outer cylinder portion. 
     This configuration can more reliably prevent a positional shift of the liner portion, and contribute to stabilization of an operation state of the uniaxial eccentric screw pump. 
     In the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention, the liner portion may have a polygonal outward shape. 
     With this configuration, it is possible to prevent the positional shift of the liner portion in a peripheral direction, and to further stabilize the operation state of the uniaxial eccentric screw pump. 
     Further, in the uniaxial eccentric screw pump according to the exemplary embodiment of the present invention, it is preferred that the outer cylinder portion be bent into a shape conforming to the outward shape of the liner portion. 
     With this configuration, it is possible to more reliably prevent the positional shift of the liner portion in the peripheral direction, and to even further stabilize the operation state of the uniaxial eccentric screw pump. 
     The uniaxial eccentric screw pump according to the exemplary embodiment of the present invention may further include a protrusion provided on an inner peripheral side of the outer cylinder portion. The protrusion may be held in press-contact with an outer peripheral surface of the liner portion. 
     With this configuration, the protrusion is engaged on the outer peripheral surface of the liner portion by being pressed, and hence the positional shift of the liner portion can be reliably prevented. Thus, this configuration is effective particularly in a case where there is a fear of the positional shift of the liner portion as in a case where the outward shape of the liner portion is cylindrical. 
     According to the present invention, it is possible to provide the uniaxial eccentric screw pump enabling the stator to be easily separated into the outer cylinder and the lining member, and being capable of solving the problems such as the positional shift and deformation of the lining member, and the occurrence of uneven wear and the unstable discharge amount associated with the positional shift and deformation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view illustrating a uniaxial eccentric screw pump according to an embodiment of the present invention; 
         FIG. 2(   a ) is an enlarged view of a portion α of  FIG. 1 , and  FIG. 2(   b ) is an enlarged view of a portion β of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of a stator; 
         FIG. 4  are views illustrating the stator adopted in the uniaxial eccentric screw pump illustrated in  FIG. 1 ; 
         FIG. 4(   a ) is a front view of the stator; 
         FIG. 4(   b ) is a side view thereof; 
         FIG. 4(   c ) is a cross-sectional view taken along the line A-A of  FIG. 4(   a ); 
         FIG. 5  are views illustrating a liner portion adopted in the stator illustrated in  FIG. 3 ; 
         FIG. 5(   a ) is a front view of the liner portion; 
         FIG. 5(   b ) is a side view thereof; 
         FIG. 5(   c ) is a cross-sectional view taken along the line C-C of  FIG. 5(   b ); 
         FIG. 5(   d ) is a cross-sectional view taken along the line B-B of  FIG. 5(   a ); 
         FIG. 6  is an explanatory diagram illustrating a way of fitting a sandwiching piece to a clamped portion when clamp joining outer cylinder components; and 
         FIG. 7  is a front view illustrating an exploded state of a stator according to a modification of the embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Next, a uniaxial eccentric screw pump  10  according to an embodiment of the present invention is described in detail with reference to the drawings. The uniaxial eccentric screw pump  10  is a so-called rotary positive displacement pump, and as illustrated in  FIG. 1 , includes a stator  20 , a rotor  50 , and a power transmission mechanism  70 . Further, the uniaxial eccentric screw pump  10  includes a cylindrical pump casing  12  made of a metal and an end stud  13 , and has structure in which the cylindrical pump casing  12  and the end stud  13  are connected to and integrated with each other through the intermediation of a stay bolt  18  (screw rod). In the uniaxial eccentric screw pump  10 , a first opening  14   a  is formed in the end stud  13 , and a second opening  14   b  is formed in an outer peripheral part of the pump casing  12 . The first opening  14   a  is a through-hole formed through the uniaxial eccentric screw pump  10  in its axial direction. The second opening  14   b  is communicated to an internal space of the pump casing  12  at an intermediate portion  12   a  that is situated in an intermediate part of the pump casing  12  in a longitudinal direction. 
     The first opening  14   a  and the second opening  14   b  function as a suction port and a discharge port of the uniaxial eccentric screw pump  10 , respectively. More specifically, the uniaxial eccentric screw pump  10  according to this embodiment can transfer fluid under pressure by rotating the rotor  50  in a forward direction so that the first opening  14   a  functions as the discharge port and the second opening  14   b  functions as the suction port. Conversely, the uniaxial eccentric screw pump  10  can transfer the fluid under pressure by rotating the rotor  50  in a reverse direction so that the first opening  14   a  functions as the suction port and the second opening  14   b  functions as the discharge port. 
     As illustrated in  FIG. 1  and  FIGS. 2 , at a part (end portion  12   b ) facing the end stud  13  side in a state in which the uniaxial eccentric screw pump  10  is assembled, the pump casing  12  includes a fitting portion  12   c  formed to have a stepped cross-sectional shape. Further, at a part (end portion  13   a ) facing the pump casing  12  side in the state in which the uniaxial eccentric screw pump  10  is assembled, the end stud  13  includes a fitting portion  13   b  formed to have a stepped cross-sectional shape. Each of the fitting portions  12   c ,  13   b  is provided so as to fit thereto a flange portion  26  of the stator  20 , which is described in detail later. A width h 1  (axial length) of the fitting portion  12   c ,  13   b  is substantially equal to a thickness (axial length) of the flange portion  26 , and an opening diameter h 2  of a part provided with the fitting portion  12   c ,  13   b  is substantially equal to an outer diameter of the flange portion  26 . 
     The uniaxial eccentric screw pump  10  includes a stator fixing portion  15  for fixing the stator  20  between the pump casing  12  and the end stud  13 . In the uniaxial eccentric screw pump  10 , through mounting of the stay bolt  18  in a state in which the stator  20  is arranged on the stator fixing portion  15 , the pump casing  12  and the end stud  13  are coupled to each other through the intermediation of the stator  20 , thereby forming a series of flow passages connecting between the first opening  14   a  and the second opening  14   b  described above. 
     The stator  20  is the most characteristic part in the uniaxial eccentric screw pump  10 . As illustrated in  FIG. 1 ,  FIG. 3 , and  FIGS. 4 , the stator  20  is divided roughly into a liner portion  22  and an outer cylinder portion  24 . The liner portion  22  is integrally formed of a resin, an elastic material typified by rubber, or the like. A material of the liner portion  22  is selected as appropriate depending on a kind, a property, and the like of the fluid as an object to be conveyed, which is to be transferred using the uniaxial eccentric screw pump  10 . 
     The liner portion  22  is a cylinder which includes, at both axial end portions, the flange portions  26 ,  26 (collar portions) protruding radially outward, and includes an outer cylinder mounting portion  28  for mounting thereon the outer cylinder portion  24  between the flange portions  26 ,  26 . The liner portion  22  is a member obtained by integrally forming the flange portions  26 ,  26  and the outer cylinder mounting portion  28 , and includes a step  30  at a boundary part between each of the flange portions  26 ,  26  and the outer cylinder mounting portion  28 . An outward shape (cross-sectional shape) of each of the flange portions  26 ,  26  is substantially circular, and an outward shape (cross-section I shape) of the outer cylinder mounting portion  28  is polygonal (substantially regular decagonal in this embodiment). Further, as described above, the thickness of each of the flange portions  26 ,  26  is substantially equal to the width h 1  of the fitting portion  12   c  provided at the end portion  12   b  of the pump casing  12  and the width h 1  of the fitting portion  13   b  provided at the end portion  13   a  of the end stud  13 . The outer diameter of each of the flange portions  26 ,  26  is substantially equal to the opening diameter h 2  of the fit ting portion  12   c  provided at the end portion  12   b  of the pump casing  12  and the opening diameter h 2  of the fitting portion  13   b  provided at the end portion  13   a  of the end stud  13 . 
     In an inner peripheral surface  32  of the liner portion  22 , a multi-stage internal thread shape is formed. More specifically, in an inside of the liner portion  22 , there is formed a through-hole  34  extending along the longitudinal direction of the liner portion  22 , threaded through at a predetermined pitch, and having an internal thread shape. The through-hole  34  is formed to have a substantially elliptical cross-sectional shape (opening shape) in cross-sectional view taken from any position in the longitudinal direction of the liner portion  22 . 
     As illustrated in  FIG. 3  and  FIGS. 4 , the outer cylinder portion  24  covers an outer periphery of the above-mentioned liner portion  22  and is mounted in a non-bonded state over the outer cylinder mounting portion  28  of the liner portion  22 . Specifically, the outer cylinder portion  24  is mounted in a pressed state on the outer periphery of the liner portion  22 , integrated with the liner portion  22  without using an adhesive, and positioned both in a peripheral direction and in the axial direction. 
     The outer cylinder portion  24  includes a plurality of (two in this embodiment) outer cylinder components  36 ,  36  and clamps  38 ,  38 . Each of the outer cylinder components  36 ,  36  is a metal member covering substantially a half of a peripheral region of the outer cylinder mounting portion  28  of the liner portion  22 , and is curved (bent) into a shape conforming to the outer cylinder mounting portion  28 . Therefore, through mounting of the outer cylinder component  36  on the outer cylinder mounting portion  28 , the outer cylinder component  36  is prevented from turning in the peripheral direction. Further, as illustrated in  FIG. 4(   c ), the thickness of the outer cylinder component  36  is larger than the height of the step  30  formed between the flange portion  26  and the outer cylinder mounting portion  28  in the liner portion  22 . Therefore, when mounting the outer cylinder component  36  on the outer cylinder mounting portion  28 , as illustrated in  FIG. 1  and  FIGS. 4 , the outer cylinder component  36  projects radially outward of the liner portion  22  with respect to the flange portion  26 . 
     Further, the length of the outer cylinder component  36  is substantially equal to the length of the outer cylinder mounting portion  28 . Therefore, when mounting the outer cylinder component  36  on the outer cylinder mounting portion  28 , as illustrated in  FIG. 1 ,  FIGS. 2 , and  FIGS. 4 , both end portions of the outer cylinder component  36  abut on the flange portions  26 ,  26  at the parts of the liner portion  22  at which the steps  30  are formed. Therefore, in a case where compressive stress acts in the axial direction (longitudinal direction) in a state in which the outer cylinder components  36  are mounted on the liner portion  22 , the outer cylinder portion  24  receives the stress by the outer cylinder components  36 , and thus can prevent compressive deformation of the liner portion  22  and deformation of the through-hole  34  formed in the liner portion. 
     At both peripheral end portions of the outer cylinder portion  24 , clamped portions  40 ,  40  are formed so as to extend in the longitudinal direction. On one end side of the clamped portions  40 ,  40 , pin insertion holes  42 ,  42  are provided, and engagement grooves  44 ,  44  are formed on the other end side thereof. The pin insertion holes  42 ,  42  and the engagement grooves  44 ,  44  are used for mounting the clamps  38 ,  38  which are described in detail later. The engagement groove  44  is formed so as to extend obliquely rearward (to the other end side) from an edge of the clamped portion  40 . 
     The clamp  38  includes a sandwiching piece  46  having a substantially C-shaped cross-section, and a pin  48 . When mounting the outer cylinder components  36  on the outer cylinder mounting portion  28 , the sandwiching piece  46  is mounted so as to sandwich the clamped portions  40 ,  40  which are in an overlapping state. The sandwiching piece  46  has a length substantially equal to that of the clamped portion  40 . On one longitudinal end side of the sandwiching piece, pin insertion holes  46   a  are formed, and protrusions  46   b  are provided on the other longitudinal end side thereof. In a state in which, as indicated by an arrow X of  FIG. 6 , each of the protrusions  46   b  is slid along the engagement groove  44  which is formed in the clamped portion  40  so as to extend obliquely, and each of the protrusions  46   b  abuts on an end portion of the engagement groove  44 , the sandwiching piece  46  is pivoted about the protrusions  46   b  as indicated by an arrow Y of  FIG. 6 , with the result that it is possible to obtain a state in which the pin insertion holes  46   a  are communicated to the pin insertion holes  42 ,  42  on the flanges  40 ,  40  side. In this state, through insertion of the pin  48  through all the pin insertion holes  46   a ,  42 , and  42 , the flanges  40 ,  40  can be sandwiched and fixed (clamp joined) by the clamp  38 . 
     The stator  20  is used in a state in which the liner portion  22  is covered with the outer cylinder components  36 ,  36  and the clamped portions  40 ,  40  are joined by the clamps  38 ,  38 . The stator  20  is incorporated in a stator fixing portion  12   b  situated adjacent to the first opening  14   a  in the pump casing  12 . Specifically, the stator  20  is fixed in such a manner that the flange portions  26 ,  26  provided at both ends of the liner portion  22  are inserted into the fitting portion  12   c  of the pump casing  12  and the fitting portion  13   b  of the end stud  13  to be sandwiched between the end stud  13  and the intermediate portion  12   a  (in the stator fixing portion  12   b ), and the stay bolt  18  is fitted and fastened across the end stud  13  and a main body part of the pump casing  12 . 
     When the stator  20  is fixed in the above-mentioned manner, as illustrated in  FIG. 2(   a ), one of the flange portions  26  is sandwiched between the end stud  13  and the outer cylinder portion  24  on one end side of the liner portion  22 . Further, as illustrated in  FIG. 2(   b ), on the other end side thereof, the other of the flange portions  26  is sandwiched between the intermediate portion  12   a  and the outer cylinder portion  24 . In addition, the outer cylinder portion  24  abuts on the flange portion  26  and the end portion of the end stud  13  on one end side of the outer cylinder portion  24 , and abuts on the flange portion  26  and the end portion of the pump casing  12  on the other end side thereof. Therefore, in the stator  20 , positional shifts and the like of both of the liner portion  22  and the outer cylinder portion  24  do not occur in the stator fixing portion  12   b  of the pump casing  12 . 
     As illustrated in  FIG. 1 , the rotor  50  is a metal shaft, and has a single-start, multi-stage, and eccentric external thread shape. The rotor  50  is formed to have a substantially complete round cross-sectional shape in cross-sectional view taken from any position in its longitudinal direction. The rotor  50  is inserted through the through-hole  34  formed in the above-mentioned stator  20 , and can freely and eccentrically rotate inside the through-hole  34 . 
     When the rotor  50  is inserted through the through-hole  34  formed in the liner portion  22  of the stator  20 , an outer peripheral surface  52  of the rotor  50  and the inner peripheral surface  32  of the stator  20  abut on each other along tangent lines of both of the peripheral surfaces. Further, in this state, between the inner peripheral surface  32  of the stator  20  and the outer peripheral surface of the rotor  50 , a fluid conveying passage  60  is formed. 
     The fluid conveying passage  60  extends in a spiral shape in the longitudinal direction of the stator  20  and the rotor  50 . Further, when the rotor  50  is rotated inside the through-hole  34  of the stator  20 , the fluid conveying passage  60  advances in the longitudinal direction of the stator  20  while rotating inside the stator  20 . Therefore, when the rotor  50  is rotated, the fluid is sucked into the fluid conveying passage  60  from one end side of the stator  20 , and the fluid is transferred to the other end side of the stator  20  while being confined inside the fluid conveying passage  60 . In this manner, it is possible to discharge the fluid to the other end side of the stator  20 . That is, when the rotor  50  is rotated in the forward direction, it is possible to transfer under pressure the fluid sucked from the second opening  14   b , and to discharge the fluid from the first opening  14   a . Further, when the rotor  50  is rotated in the reverse direction, it is possible to discharge from the second opening  14   b  the fluid sucked from the first opening  14   a.    
     The power transmission mechanism  70  is provided so as to transmit power from a power source (not shown), such as a motor provided outside the pump casing  12 , to the above-mentioned rotor  50 . The power transmission mechanism  70  includes a power connecting portion  72  and an eccentric rotary portion  74 . The power connecting portion  72  is provided in a shaft accommodating portion  12   c  provided on one longitudinal end side of the pump casing  12 , more specifically, on the side (hereinafter, simply referred to as “proximal end side”) opposite to the side on which the above-mentioned end stud  13  and the stator fixing portion  12   b  are provided. Further, the eccentric rotary portion  74  is provided in the intermediate portion  12   a  formed between the shaft accommodating portion  12   c  and the stator fixing portion  12   b.    
     The power connecting portion  72  includes a drive shaft  76 , and the drive shaft is supported by two bearings  78   a ,  78   b  so as to be freely rotatable. The drive shaft  76  sticks out of a closed part on the proximal end side of the pump casing  12 , and is connected to the power source. Therefore, through activation of the power source, the drive shaft  76  can be rotated. Between the intermediate portion  12   a  and the shaft accommodating portion  12   c  in which the power connecting portion  72  is provided, a shaft sealing device  80  formed of, for example, a mechanical seal or a gland packing is provided. This provides the structure in which the fluid as an object to be conveyed does not leak from the intermediate portion  12   a  side to the shaft accommodating portion  12   c  side. 
     The eccentric rotary portion  74  connects between the above-mentioned drive shaft  76  and the rotor  50  so as to allow power transmission there between. The eccentric rotary portion  74  includes a coupling shaft  82  and two coupling bodies  84 ,  86 . The coupling shaft  82  is formed of a conventionally-known coupling rod, screw rod, or the like. The coupling body  84  couples the coupling shaft  82  and the rotor  50  to each other, and the coupling body  86  couples the coupling shaft  82  and the drive shaft  76  to each other. The coupling bodies  84 ,  86  are both formed of a conventionally-known universal joint or the like. The coupling bodies  84 ,  86  can transmit to the rotor  50  rotational power transmitted through the drive shaft  76 , to thereby rotate the rotor  50  eccentrically. 
     As described above, in the stator  20  of the uniaxial eccentric screw pump  10  according to this embodiment; the outer cylinder portion  24  is mounted in a non-bonded state on the liner portion  22  that is integrally formed. Specifically, due to an influence of a sandwiching force generated by mounting the clamp  38  on the clamped portions  40 ,  40  of the outer cylinder components  36 ,  36 , a pressing force in a radially inward direction of the outer cylinder portion  24  acts on the liner portion  22 . Due to the pressing force, the outer cylinder portion  24  is mounted in a pressed state on the outer periphery of the liner portion  22 , and is positioned in the axial direction and the peripheral direction of the liner portion  22 . Therefore, the uniaxial eccentric screw pump  10  enables the liner portion  22  and the outer cylinder portion  24  to be easily separated and recovered through dismounting of the outer cylinder components  36 ,  36  and the clamps  38 ,  38 . Thus, it is possible to give due consideration to environmental issues. 
     Further, the uniaxial eccentric screw pump  10  has structure in which the outer cylinder portion  24  covers the outer cylinder mounting portion  28  that is present between the flange portions  26  provided at both the end portions of the liner portion  22 , and that the end portions of the outer cylinder portion  24  abut on the flange portions  26 . This structure can prevent the liner portion  22  from shrinking in the axial direction. That is, the outer cylinder portion  24  functions as a support for preventing the liner portion  22  from shrinking in the axial direction. This can keep an inner diameter of the liner portion  22  substantially uniform at any part even when a compression force in the axial direction acts on the stator  20  due to an influence of discharge pressure and the like. Thus, it is possible to avoid uneven wear of the liner portion  22 , and to stabilize a discharge amount. 
     According to the uniaxial eccentric screw pump  10 , the outer cylinder portion  24  can be divided into the plurality of outer cylinder components  36  in the peripheral direction, and hence it is possible to easily perform work of mounting/dismounting the outer cylinder portion  24  to/from the liner portion  22 . Further, the above-mentioned outer cylinder portion  24  is an integrated member obtained by joining (clamp joining) the outer cylinder components  36  with each other using the clamps  38 , and hence the outer cylinder portion  24  can be mounted/dismounted simply by mounting/dismounting the sandwiching pieces  46  and the pins  48  to/from the clamped portions  40 ,  40 . 
     Note that, in this embodiment, an example of constituting the outer cylinder portion  24  by the two outer cylinder components  36  is exemplified, but the present invention is not limited thereto. Alternatively, the outer cylinder portion  24  may be formed of even more outer cylinder components  36 . Further, in this embodiment, an example of joining the outer cylinder components  36 ,  36  together by the clamps  38  at two peripheral points is exemplified, but the present invention is not limited thereto. For example, there can be adopted structure in which one peripheral end side of the outer cylinder components  36 ,  36  is coupled by a hinge or the like, and the other peripheral end side thereof is coupled by the clamp  38  or another method. In addition, in this embodiment, an example of using the clamp  38  formed of the sandwiching piece  46  and the pin  48  in order to join the outer cylinder components  36 ,  36  together is exemplified, but the present invention is not limited thereto. As long as the outer cylinder components  36 ,  36  can be fixed so as not to be shifted in position, the outer cylinder components  36 ,  36  may be joined together using any other method. 
     According to the uniaxial eccentric screw pump  10  of this embodiment, the end stud  13  is arranged on one end side of the stator  20 , and the stator  20  is integrally coupled to the pump casing  12  together with the end stud  13  using a fastening force generated by the stay bolt  18 . Further, in the stator  20 , the outer cylinder portion  24  abuts on the end portion  12   b  of the pump casing  12  and the end portion  13   a  of the end stud  13 . Therefore, in a state in which the stator  20  is assembled, the fastening force generated by the stay bolt  18  acts more preferentially on the outer cylinder portion  24  than on the liner portion  22 , and hence it is possible to prevent action of a large compression force in the axial direction on the liner portion  22 , and compressive deformation of the liner portion  22 . Further, this can prevent uneven wear of the liner portion  22 , and stabilize the discharge amount. 
     According to the uniaxial eccentric screw pump  10  of this embodiment, at the end portion  12   b  of the pump casing  12  and the end portion  13   a  of the end stud  13 , the fitting portions  12   c ,  13   b  for enabling the flange portions  26  to be fitted thereon are respectively provided. The flange portions  26  of the liner portion  22  fitted to the fitting portions are sandwiched between the outer cylinder portion  24  and the end stud  13  and between the outer cylinder portion  24  and the pump casing  12 . This can reliably prevent a positional shift of the liner portion  22  in the axial direction, and can further stabilize an operation state of the uniaxial eccentric screw pump  10 . 
     As described above, the outward shape of the outer cylinder mounting portion  28  of the liner portion  22  is polygonal (substantially decagonal in this embodiment). In addition, each of the outer cylinder components  36 ,  36  is bent into a shape conforming to the outer cylinder mounting portion  28 . Through clamping and joining of the clamped portions  40  by the clamps  38 , the outer cylinder portion  24  having a cylindrical shape and substantially the same shape (substantially regular decagonal shape in this embodiment) as that of the outer cylinder mounting portion  28  is formed. Thus, even when a load in the peripheral direction acts on the liner portion  22 , it is possible to prevent only the liner portion  22  from being shifted in position in the peripheral direction, and to stabilize the operation state of the uniaxial eccentric screw pump  10 . 
     Note that, in this embodiment, such an example is exemplified that, in order to prevent the liner portion  22  from being shifted in position with respect to the outer cylinder portion  24 , each of the outer cylinder mounting portion  28  and the outer cylinder portion  24  is formed into a polygonal shape. However, in a case of adopting another configuration capable of preventing the positional shift in the peripheral direction, or in a case of requiring no consideration of the positional shift in the peripheral direction, a configuration different from the above-mentioned configuration may be adopted. Specifically, the outer cylinder mounting portion  28  and the outer cylinder portion  24  have substantially the same cross-sectional shape, but, for example, as in a configuration in which the outer cylinder mounting portion  28  is formed into a substantially regular decagonal shape and the outer cylinder portion  24  is formed into a substantially regular dodecagonal shape, the cross-sectional shapes of both the portions may be different from each other as long as the outer cylinder mounting portion  28  and the outer cylinder portion  24  function to prevent turning of the liner portion  22 . 
     Further, there may be adopted a configuration in which protrusions  90  are provided on an inner peripheral side of the outer cylinder portion  24  and, through mounting of the outer cylinder portion  24  on the outer cylinder mounting portion  28 , the above-mentioned protrusions  90  are held in press-contact with an outer peripheral surface of the liner portion  22 . With this configuration, the protrusions  90  are caught on the outer peripheral surface of the liner portion  22 , and hence it is possible to prevent the liner portion  22  from being shifted in position in the peripheral direction and the axial direction. The configuration in which the protrusions  90  are provided in this manner is effective not only in a case where the outer cylinder mounting portion  28  and the outer cylinder portion  24  are each formed into a polygonal shape as in this embodiment, but also in a case where there is a fear of the positional shift of the liner portion  22  as in a case where the outward shape of the liner portion  22  is cylindrical.