Patent Publication Number: US-2018038389-A1

Title: Compressor system, and attachment structure for centrifugal separator

Description:
TECHNICAL FIELD 
     The present invention relates to a compressor system and an attachment structure for a centrifugal separator. 
     The present application claims priority rights concerning Japanese Unexamined Patent Application 2015-058367, submitted on Mar. 20, 2015; Japanese Unexamined Patent Application 2015-058368, submitted on Mar. 20, 2015; and Japanese Unexamined Patent Application 2015-058681, submitted on Mar. 20, 2015; and contents thereof are incorporated herein by reference. 
     BACKGROUND ART 
     A compressor system (motor compressor) wherein a motor and a compressor are in one body has a compressor for compressing gases such as air and gas, and a motor for driving the compressor. A compressor system (motor compressor) has a rotation shaft extending from the casing of the compressor connected with a rotation shaft of the motor, which similarly extends from the motor casing. The rotation of the motor is transmitted to the compressor. The rotation shaft of the motor and compressor rotate stably because they are supported by a plurality of bearings. 
     For example, such a compressor system (motor compressor) is used in a Subsea Production System as in Non-patent Document 1, or a Floating Production Storage and Offloading facility (FPSO) as in Non-patent Document 2. When used in the subsea production system, the compressor system (motor compressor) is disposed on a sea bed, and feeds out a production fluid, which is a mixture of crude oil, natural gas, and the like, to the sea surface from a production well drilled to a depth of several thousand meters below the sea bed. When used in a floating production storage and offloading facility, the compressor system (motor compressor) is disposed on the sea surface facility, such as a ship. 
     CITATION LIST 
     Non-Patent Documents 
     
         
         Non-patent document 1: Mitsubishi Industrial Report Vol. 34 No. 5 
         Non-patent document 2: Turbomachinery International September/October 2014 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, with a conventional compressor system, the production fluid, which is a mixture of crude oil, natural gas, and the like, is supplied to the compressor after the gas and liquid have been separated. As such, a centrifugal pump is provided on the upstream side of the compressor for separating gas and liquid. However, when using a centrifugal pump, there is a possibility of the water head decreasing and the function of the pump declining if cavitation occurs. There is room for improvement concerning this point. 
     If the function of the pump declines and the gas-liquid separation becomes insufficient, fluid is introduced to the compressor with liquid (a foreign substance) mixed therein. Because of this, there have been problems in the impeller of the compressor being damaged. 
     Such a centrifugal pump is provided on the upstream side of the compressor. With a centrifugal pump, there are many foreign substances included in the introduced fluid. Because of this, centrifugal pumps wear quickly, and the frequency of exchange increases. A conventional centrifugal pump is commonly fixed via a bolt fastener. However, improvement in work efficiency is desired, as it is attachment and removal work via bolts in a limited space. There is room for improvement concerning this point. 
     When the yield strength of the bolt is insufficient relative to the centrifugal pump which generates a large centrifugal force, there is a risk of the centrifugal pump not being able to maintain a stable state. 
     With the foregoing in view, a first object of the present invention is to provide a compressor system which, by efficiently separating foreign substances within a fluid, can mitigate mixture of foreign substances into an impeller and prevent damage to an impeller. 
     With the foregoing in view, a second object of the present is to provide an attachment structure for a centrifugal separator which can improve work efficiency while improving the resistance against the centrifugal force, by performing the attachment and removal work in a simple manner. 
     Solution to Problem 
     To accomplish the first object, a compressor system of a first mode of the present invention is composed of a drive part, an impeller for pressure-feeding a fluid radially outward after the fluid has flowed in from an axial direction by rotating around the shaft line via the drive part, a centrifugal separator provided on the upstream side of the impeller and formed to be larger than the outer diameter of the inlet of the impeller, which feeds the externally supplied fluid out toward the impeller while causing the fluid to swirl by rotating around the shaft line via the drive part, and a casing for sectioning off an inflow channel which guides the fluid from the exterior to the centrifugal separator, a first accommodation space which is disposed downstream from the inflow channel and which accommodates the centrifugal separator, a second accommodation space which is connected to the downstream side of the first accommodation space and which accommodates the impeller, and a foreign substance expulsion channel which is connected downstream of the first accommodation space in the axial direction and expels foreign substances guided to the outer peripheral side by the centrifugal separator. 
     Such a configuration allows the fluid externally supplied via the inlet channel to the first accommodation space to be accommodated in the first accommodation space and swirled by the centrifugal separator, which rotates around the shaft line via the drive part. The swirled fluid is fed out toward the impeller, which is disposed on the downstream side of the centrifugal separator. At this time, in the first accommodation space, foreign substances with large mass in the fluid are guided radially outward by the centrifugal force which is generated by the centrifugal separator. The foreign substances in the fluid which are guided axially and radially outward by the centrifugal separator are expelled by flowing into a foreign substance expulsion channel, which is connected on the downstream side of the first accommodation space. In other words, the centrifugal separator has a larger diameter than the inlet of the impeller, and the foreign substance expulsion channel is connected at the step portion of the outlet outer diameter of the centrifugal separator and the inlet outer diameter of the impeller. Because of this, the foreign substances which are fed out radially outward flow into the foreign substance expulsion channel and are collected. 
     Other fluid with lower mass than the foreign substance which flows into the foreign substance expulsion channel is fed out in the axial direction, flows into the impeller which is on the downstream side of the centrifugal separator, and is pressure-fed radially outward by the rotation of the impeller. Because of this, foreign substances contained in the fluid are separated upstream of the impeller. This allows for the mitigation of foreign substances mixing into the impeller, and can prevent damage to the impeller. 
     In this manner, the foreign object expulsion channel is connected on the outside in the radial direction on the downstream side of the centrifugal separator. As a result, foreign substances guided radially outward by centrifugal force can be efficiently collected. Because of this, when, for example, a liquid is mixed in a fluid which is mainly a gas, the liquid can be guided radially outward by the centrifugal force of the centrifugal separator and collected by the foreign substance expulsion channel. This imparts the function of gas-liquid separation. 
     In the compressor system of a second mode of the present invention, the foreign object expulsion channel of the first mode preferably extends from the first accommodation space toward the impeller side in the axial direction and radially outward. 
     Such a configuration makes for a shape which has the direction of the channel of the inflow portion of the foreign substance expulsion channel matches the direction of the flow of the foreign substance guided by the centrifugal force of the centrifugal separator. Because of this, the foreign substance can be made to efficiently flow into the foreign substance expulsion channel. 
     In the compressor system of a third mode of the present invention, the casing of the first or second mode preferably sections off a foreign substance collection chamber which is connected to the foreign substance expulsion channel. 
     Such a configuration allows the foreign substances flowing into the foreign substance expulsion channel to be gathered and collected in the foreign substance collection chamber, which is sectioned off by the casing. 
     In the compressor system of a fourth mode of the present invention, the diameter of the channel cross section of the foreign substance expulsion channel of any one of the first to third modes progressively gets smaller from the upstream side to the downstream side. 
     Such a configuration allows for an increased flow speed of the fluid (foreign substance) passing through the foreign substance expulsion channel, thereby reducing the pressure; this mitigates damage done to the casing by the pressure of the foreign substance passing through the foreign substance expulsion channel. 
     To accomplish the first object, the compressor system of a fifth mode of the present invention is composed of a drive part, an impeller for pressure-feeding a fluid radially outward after the fluid has flowed in from an axial direction by rotating around the shaft line via the drive part, a centrifugal separator provided on the upstream side of the impeller, which feeds the externally supplied fluid out toward the impeller while causing the fluid to swirl by rotating around the shaft line via the drive part, and a casing for sectioning off an inflow channel which guides the fluid from the exterior to the centrifugal separator, a first accommodation space which is disposed downstream from the inflow channel and which accommodates the centrifugal separator, a second accommodation space which is connected to the downstream side of the first accommodation space and which accommodates the impeller, and a foreign substance expulsion channel which is connected downstream of the first accommodation space in the axial direction and expels foreign substances guided to the outer peripheral side by the centrifugal separator. 
     Such a configuration allows the fluid externally supplied via the inlet channel to the first accommodation space to be accommodated in the first accommodation space and swirled by the centrifugal separator, which rotates around the shaft line via the drive part. The swirled fluid is fed out toward the impeller, which is disposed on the downstream side of the centrifugal separator. At this time, in the first accommodation space, foreign substances with large mass in the fluid are guided radially outward by the centrifugal force which is generated by the centrifugal separator. The foreign substance in the fluid which is guided radially outward by the centrifugal separator flows into the foreign substance expulsion channel which extends radially outward from the first accommodation space, and is expelled and collected. 
     Other fluid with lower mass than the foreign substance which flows into the foreign substance expulsion channel is fed out in the axial direction, flows into the impeller which is on the downstream side of the centrifugal separator, and is pressure-fed radially outward by the rotation of the impeller. Because of this, foreign substances contained in the fluid are separated upstream of the impeller. This allows for the mitigation of foreign substances mixing into the impeller, and can prevent damage to the impeller. 
     In this manner, the present invention is a configuration such that the foreign substance expulsion channel is connected so it extends outward in the radial direction of the first accommodation space. The foreign substance expulsion channel is a smooth channel along the axial direction and is formed so that there is no ridge or the like in the first accommodation space and at the connection portion between the first accommodation space and the second accommodation space. This inhibits the occurrence of turbulent flow, and allows the foreign substances guided radially outward by centrifugal force to be efficiently collected. Because of this, when, for example, a liquid is mixed in a fluid which is mainly a gas, the liquid can be guided radially outward by the centrifugal force of the centrifugal separator and collected by the foreign substance expulsion channel. This imparts the function of gas-liquid separation. 
     In the compressor system of a sixth mode of the present invention, the casing of the fifth mode preferably sections off a foreign substance collection chamber which connects to the foreign substance expulsion channel and extends over the entire periphery along the circumferential direction around the shaft line. 
     Such a configuration allows the foreign substance flowing into a plurality of foreign substance expulsion channels to be gathered and collected in one foreign substance collection chamber which extends over the entire periphery of the circumferential direction and is sectioned off by the casing. 
     In the compressor system of a seventh mode of the present invention, a plurality of the foreign substance expulsion channel of the fifth or sixth mode is provided in the circumferential direction around the shaft line. These foreign substance expulsion channels are preferably disposed in a pressure region which causes the pressure of the fluid in the circumferential direction of the first accommodation space to be equal. 
     According to such a configuration, fluid (foreign substance) at an equal pressure can flow into the plurality of foreign substance expulsion channels disposed along the circumferential direction, thereby allowing the pressure balance of the fluid in the first accommodation space to be stabilized, and the foreign substance flowing into the foreign substance expulsion channel can be prevented from returning to the first accommodation space. 
     In the compressor system of an eighth mode of the present invention, a plurality of the foreign substance expulsion channel of any one of the fifth to the seventh modes is preferably provided along the axial direction of the first accommodation space. 
     In this case, the fluid (foreign substance) guided radially outward by the centrifugal force of the centrifugal separator can be gradually collected via the foreign substance expulsion channels in a plurality of locations along the axial direction of the first accommodation space. This improves the gas-liquid separation function. 
     To accomplish the second objective, the attachment structure for a centrifugal separator of a ninth mode of the present invention is an attachment structure for a centrifugal separator which is provided on the upstream side of an impeller which pressure-feeds a fluid radially outward after the fluid has flowed in from an axial direction by rotating around the shaft line via the drive part, and feeds the externally supplied fluid out toward the impeller while causing the fluid to swirl by rotating around a rotation shaft on the same shaft as the shaft line via the drive part, wherein the centrifugal separator has two protruding parts provided thereon which protrude toward both sides in the axial direction from a base part of the rotation shaft side, a first protruding part, of the two protruding parts, is pressed from the outer peripheral side by a holding recessed part provided on a holding part provided as one body on the rotation shaft, and a second protruding part, which is pressed from the outer peripheral side by a fitting member which can be attached and removed relative to the rotation shaft. 
     According to such a configuration, the centrifugal separator is attached to the rotation shaft in a state that protruding parts protruding on both sides of the axial direction from the base thereof are pressed from the outer peripheral side by a holding part and a fitting member. In other words, the base of the centrifugal separator is pressed in the direction opposite the centrifugal force which acts radially outward. As a result, resistance against centrifugal force can be increased. Furthermore, for example, in a case where the holding part provided as one body on the rotation shaft is the rotor of the drive part, one first protruding part is pressed on its entire periphery by the rotor, thereby securing stability and high strength. 
     The fitting member which presses the other second protruding part from the outer peripheral side is attachable and removable relative to the rotation shaft. Thus, by freeing the fitting of the fitting member relative to the rotation shaft, the press on the second protruding part can be released, and the centrifugal separator can easily be removed from the rotation shaft. 
     This makes it possible to improve the work efficiency when attaching and removing the centrifugal separator. Because of this, there is the advantage of being able to efficiently exchange or perform maintenance such as cleaning for the centrifugal separator. 
     In the attachment structure for a centrifugal separator of a tenth mode of the present invention, the fitting member is provided on the same shaft as the rotation shaft, and is provided with a female screw which screws into the outer peripheral surface of the rotation shaft, and a fitting recessed part, which fits from the outer peripheral side relative to the second protruding part. 
     In this case, when detaching the centrifugal separator from the rotation shaft, the screw attachment relative to the rotation shaft is freed by rotating the nut-style fitting member in the direction that the screw loosens. This allows the pressing of the fitting recessed part relative to the second protruding part to be released. 
     In the attachment structure for a centrifugal separator of an eleventh mode of the present invention, the centrifugal separator of the ninth or tenth mode may be divided in the circumferential direction. 
     In this case, the centrifugal separator, which is divided in the circumferential direction, can be detached from the rotation shaft by simply freeing the fitting of the fitting member relative to the second protruding part. In other words, the centrifugal separator can be exchanged without performing work to free the rotor connected to the rotation shaft from the rotation shaft. In particular, in the case that the fitting member is of the nut-style described above, the work of completely detaching the fitting member from the rotation shaft becomes unnecessary. 
     Advantageous Effects of Invention 
     According to the compressor system of the present invention, by efficiently separating foreign substances within a fluid, it is possible to mitigate mixture of foreign substances into an impeller and prevent damage to an impeller. 
     According to the attachment structure for a centrifugal separator of the present invention, work efficiency can be improved while improving the resistance against the centrifugal force, by performing the attachment and removal work in a simple manner. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view for describing the compressor system of an embodiment of the present invention. 
         FIG. 2  is a vertical cross section view illustrating details of the compressor and centrifugal separator illustrated in  FIG. 1  of the first embodiment of the present invention; and is a drawing such that the left and right of  FIG. 1  have been switched. 
         FIG. 3  is an expanded view of important parts of the centrifugal separator illustrated in  FIG. 2 . 
         FIG. 4  is a vertical cross-sectional view illustrating details of the compressor and centrifugal separator illustrated in  FIG. 1  of a second embodiment of the present invention; and is a drawing such that the left and right of  FIG. 1  have been switched. 
         FIG. 5  is an expanded view illustrating important parts of a casing which surrounds the centrifugal separator of  FIG. 4 . 
         FIG. 6  is a drawing illustrating a first accommodation space, which is a cross-sectional view at line A-A illustrated in  FIG. 5 . 
         FIG. 7  is a drawing illustrating a first accommodation space according to a first modification, and is a drawing which corresponds to  FIG. 6 . 
         FIG. 8  is a vertical cross-sectional view illustrating a casing which surrounds a centrifugal separator according to a second modification, and is a drawing which corresponds to  FIG. 5 . 
         FIG. 9  is a vertical cross-sectional view illustrating details of the compressor and centrifugal separator illustrated in  FIG. 1  of a third embodiment of the present invention; and is a drawing such that the left and right of  FIG. 1  have been switched. 
         FIG. 10  is an expanded view of important parts of the centrifugal separator illustrated in  FIG. 9 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     The compressor system according to embodiments of the present invention is described below, with reference to the drawings. These embodiments illustrate one mode of the present invention, do not limit the present invention, and may be arbitrarily changed within a range of technical thought of the present invention. 
     A compressor system  1  is provided on a sea bed used in a Subsea Production System, which is a development style of an ocean oil-gas field, on the sea used in a Floating Production Storage and Offloading (FPSO) facility, and the like. The compressor system  1  pressure-feeds, as an operating fluid, a production fluid such as oil and gas retrieved from a production well of an oil-gas field existing from several hundred to several thousand meters below the sea bed. 
     The compressor system  1  is provided with a compressor  2 , a motor  3  (drive part), a bearing  4  (drive part), a centrifugal separator  5 , and a casing  6 , as illustrated in  FIG. 1 . The compressor  2  has a shaft  21  as a rotation shaft, which extends in the direction of an axis O (the left-right direction in  FIG. 1 ). The motor  3  has a rotor  31  which is directly connected to the shaft  21 . The bearing  4  supports the shaft  21 . The centrifugal separator  5  is provided on the upstream side of a first impeller  22  of the compressor  2 . The casing  6  accommodates the motor  3 , the compressor  2 , and the centrifugal separator  5 . 
     The compressor  2  is accommodated in the casing  6 . The compressor  2  compresses an operating fluid via the rotor  31  and the shaft  21 , which rotate around the axis O. The compressor  2  of the present embodiment has the shaft  21 , the first impeller  22 , and a housing  23 . The shaft  21  extends in the direction of the axis O. The first impeller  22  is fixed on the outer peripheral surface of the shaft  21 . The housing  23  accommodates the first impeller  22 . 
     The shaft  21  is a rotation shaft which extends in the direction of the axis O. The shaft  21  is supported by the casing  6  such that it is rotatable around the axis O. The shaft  21  penetrates the housing  23 . Both ends of the shaft  21  extend out from the housing  23 . The shaft  21  extends in the direction of the axis O in the casing  6 , which is described hereinafter. 
     The first impeller  22  rotates around the axis O with the shaft  21 , and generates compressed fluid by compressing the operating fluid which passes through the interior of the first impeller  22 . In other words, the first impeller  22  pressure-feeds the operating fluid flowing in from the direction of the axis O radially outward. 
     The housing  23  is the exterior of the compressor  2 . The housing  23  accommodates the first impeller  22  in its interior. The housing  23  is accommodated in the casing  6 . 
     The motor  3  is accommodated in the casing  6  with an open interval in the direction of the axis O relative to the compressor  2 . The motor  3  has the rotor  31  and a stator  32 . The rotor  31  is fixed so it is in one body with the shaft  21 . The stator  32  is disposed on the outer peripheral side of the rotor  31 . 
     The rotor  31  is rotatable around the axis O and is in one body with the shaft  21 . The rotor  31  is directly connected to the outer peripheral side of the shaft  21 , which is the outer side of the circumferential direction where the axis O is the reference, such that it rotates as one body with the shaft  21  of the compressor  2  without going through a gear or the like. The rotor  31  has, for example, a rotor core (not illustrated) through which induced current flows as the stator  32  generates a rotating magnetic field. 
     The stator  32  is provided covering the rotor  31  from the outer peripheral side with a gap  33  open in the circumferential direction. The stator  32  has, for example, a plurality of stator cores (not illustrated) disposed along the circumferential direction of the rotor  31 , and a stator winding (not illustrated) wound on the stator core. The stator  32  generates a rotating magnetic field as current flows from the exterior, thereby rotating the rotor  31 . The stator  32  is fixed in the casing  6 . 
     The bearing  4  is accommodated in the casing  6 . The bearing  4  rotatably supports the shaft  21 . The bearing  4  of the present embodiment is provided with a plurality of journal bearings  41  and a thrust bearing  42 . 
     The journal bearings  41  support a load which acts in the radial direction relative to the shaft  21 , with the axis O as the reference. The journal bearings  41  are disposed on both ends in the direction of the axis O of the shaft  21  so as to sandwich the motor  3  and the compressor  2  from the direction of the axis O. The journal bearings  41  are disposed between the region in which the compressor  2  is provided and the region in which the motor  3  is provided, closer to the motor  3  than a seal member  60 , described hereinafter. 
     The thrust bearing  42  supports the load acting on the shaft  21  in the direction of the axis O via a thrust collar  21   a  formed on the shaft  21 . The thrust bearing  42  is disposed between the region in which the compressor  2  is provided and the region in which the motor  3  is provided, closer to the compressor  2  than the seal member  60 , described hereinafter. 
     The centrifugal separator  5  is provided on the upstream side of the compressor  2 , as illustrated in  FIG. 2 . The centrifugal separator  5  is formed to be larger than the outer diameter of the inlet of the first impeller  22  of the compressor  2 . The centrifugal separator  5  rotates with the motor  3  around the axis O via the shaft  21 . As a result, the centrifugal separator  5  has a configuration which feeds out the externally supplied operating fluid toward the first impeller  22  while swirling it. 
     The centrifugal separator  5  is provided as a separate body from the first impeller  22  of the compressor  2 . The centrifugal separator  5  is accommodated in the casing  6 . The centrifugal separator  5  is a separator provided with a second impeller  51  fixed on the outer peripheral surface of the shaft  21  of the compressor  2 , which extends in the direction of the axis O. The radius r 1  of the second impeller  51  of the centrifugal separator  5  is set to be a larger dimension than the radius r 2  of the inlet of the first impeller  22  of the compressor  2  (r 1 &gt;r 2 ). 
     Note that the rotation shaft of the centrifugal separator  5  is shared with the shaft  21  of the compressor  2 , but it may be provided as a separate body. 
     The second impeller  51  rotates around the axis O with the shaft  21 . The second impeller  51  pressure-feeds an operating fluid, which flows in from the direction of the axis O and passes through the interior of the second impeller  51 , toward the direction of the axis O as well as radially outward, by centrifugal force. 
     The casing  6  forms a cylindrical shape along the axis O, as illustrated in  FIG. 3 . The casing  6  accommodates the compressor  2 , the motor  3 , and the centrifugal separator  5  in its interior. The inner surface of the casing  6  protrudes toward the shaft  21  between the compressor  2  and the motor  3  in the direction of the axis O. The protruding portion of the casing  6  is provided with a seal member  60  which makes a seal between the region in which the compressor  2  is provided, the region in which the centrifugal separator  5  is provided, and the region in which the motor  3  is provided. 
     The casing  6  sections off an inflow channel  61 , a first accommodation space  62 , a second accommodation space  63 , a foreign substance expulsion channel  64 , and a foreign substance collection chamber  65 . The inflow channel  61  guides the operating fluid from the exterior to the centrifugal separator  5 . The first accommodation space  62  is disposed on the downstream side of the inlet channel  61  and accommodates the centrifugal separator  5 . The second accommodation space  63  is connected on the downstream side of the first accommodation space  62 , and accommodates the first impeller  22  of the compressor  2 . The foreign substance expulsion channel  64  is connected in the direction of the axis O on the downstream side of the first accommodation space  62  and expels foreign substances in the operating fluid guided toward the outer peripheral side by the centrifugal separator  5 . The foreign substance collection chamber  65  is connected to the foreign substance expulsion channel  64 . 
     The first accommodation space  62  connects with the inflow channel  61  on one end side. The first accommodation space  62  connects with the second accommodation space  63  and the foreign substance expulsion channel  64  on the other end side. The first accommodation space  62  takes in the external operating fluid from the inflow channel  61 . The first accommodation space  62  is an interior space formed in the casing  6  so as to rotatably accommodate the second impeller  51  of the centrifugal separator  5 . 
     The foreign substance expulsion channel  64  extends from the first accommodation space  62  toward the side of the compressor  2  in the axial direction as well as radially outward. As for the foreign substance expulsion channel  64 , the diameter of the channel cross section of the foreign substance expulsion channel  64  progressively gets smaller from the upstream side to the downstream side. That is, the upstream side cross section A 1  on the first accommodation space  62  side of the foreign substance expulsion channel  64  illustrated in  FIG. 3  is larger than the downstream side cross section A 2  positioned on the foreign substance collection chamber  65  side. As illustrated in  FIG. 2 , the foreign substance expulsion channel  64  is disposed as a plurality in the circumferential direction around the axis O (on the surface of the paper, two locations above and below). 
     The foreign substance collection chamber  65  is formed in the casing  6 . The foreign substance collection chamber  65  extends over the entire periphery along the circumferential direction around the axis O. The foreign substance collection chamber  65  connects to the downstream side end part (an outlet  64   b ) of the foreign substance expulsion channel  64 . 
     The operation of the compressor system  1  of the configuration described above is described next in detail, with reference to the drawings. 
     As illustrated in  FIG. 1 , according to the compressor system  1  such as that described above, the stator  32  is supplied with electric current via an external device such as an electric generator, which is not illustrated. A rotating magnetic field is generated based on the supplied electric current, and the rotor  31  of the motor  3  starts to rotate with the shaft  21 . As the shaft  21  rotates with high speed, as illustrated in  FIG. 3 , operating fluid is supplied from the exterior via the inflow channel  61  to the first accommodation space  62 . The operating fluid is accommodated in the first accommodation space  62  and swirled by the centrifugal separator  5 , which rotates around the axis O via the motor  3 . The swirled operating fluid is fed out toward the first impeller  22  of the compressor  2  disposed on the downstream side of the centrifugal separator  5 . At this time, in the first accommodation space  62 , foreign substances with large mass in the operating fluid are guided radially outward by the centrifugal force which is generated by the centrifugal separator  5 . 
     The foreign substance of the operating fluid, which has been guided toward the axial direction and radially outward by the centrifugal separator  5 , flows into the foreign substance expulsion channel  64  which is connected on the downstream side of the centrifugal separator  5  and is expelled. The centrifugal separator  5  has a larger diameter than the inlet of the first impeller  22 , and the foreign substance expulsion channel  64  is connected at the ridge portion of the outlet outer diameter of the centrifugal separator  5  and the impeller inlet outer diameter of the compressor  2 . This causes the foreign substance fed out along the outside in the radial direction to flow into the foreign substance expulsion channel  64  and be collected in the foreign substance collection chamber  65 . 
     The other operating fluid, which has smaller mass than the foreign substance which has flowed into the foreign substance expulsion channel  64  is fed out in the axial direction and is made to flow into the first impeller  22  of the compressor  2 , which is on the downstream side of the first accommodation space  62 , and is then pressure-fed radially outward by the rotation of the first impeller  22 . This causes the foreign substance contained in the operating fluid to be separated on the upstream side of the first impeller  22 . Thus, it becomes possible to mitigate the mixing of foreign substance into the first impeller  22 , and prevent damage to the first impeller  22 . 
     In this manner, in the first embodiment, the foreign substance expulsion channel  64  is connected on the downstream side and on the outer side in the radial direction of the centrifugal separator  5 . As a result, the foreign substance which is guided radially outward by centrifugal force can be efficiently collected. Because of this, when, for example, a liquid is mixed in a fluid which is mainly a gas, the liquid can be guided radially outward by the centrifugal force of the centrifugal separator  5  and collected by the foreign substance expulsion channel  64 . This imparts the function of gas-liquid separation. Thus, when the operating fluid is a production fluid, which is a mix of crude oil, natural gas, and the like retrieved by a subsea production system as in the first embodiment, gas-liquid separation can be done efficiently, and a superior effect can be exhibited. 
     In the first embodiment, as illustrated in  FIG. 3 , the foreign substance expulsion channel  64  extends from the first accommodation space  62  on the first impeller  22  side in the axial direction, and radially outward. This makes for a shape which has the direction of the channel of the inflow portion of the foreign substance expulsion channel  64  match the direction of the flow of the foreign substance guided by the centrifugal force of the centrifugal separator  5 . This allows the foreign substance to efficiently flow into the foreign substance expulsion channel  64 . 
     In the first embodiment, a foreign substance collection chamber  65  which connects to the foreign substance expulsion channel  64  is sectioned off by the casing  6 . This allows the foreign substance that has flowed into the foreign substance expulsion channel  64  to be gathered and collected in the foreign substance collection chamber sectioned off by the casing  6 . 
     The diameter of the channel cross section of the foreign substance expulsion channel  64  progressively gets smaller from the upstream side to the downstream side. This increases the flow speed of the operating fluid (foreign substance) passing through the foreign substance expulsion channel  64 , allowing the pressure to be reduced. This allows the mitigation of damage to the casing  6  from the pressure of the foreign substance passing through the foreign substance expulsion channel  64 . 
     The compressor system according to the first embodiment described above makes it possible to mitigate the mixing of foreign substance into the first impeller  22  of the compressor  2 , and to prevent damage to the first impeller  22 , by efficiently separating the foreign substance in the operating fluid. 
     An embodiment of the compressor system according to the present invention has been described but the present invention is not limited to the aforementioned first embodiment, and may be changed as appropriate in a range that does not deviate from the main intent thereof. 
     For example, in the first embodiment, a plurality of the foreign substance expulsion channel  64  is disposed in the circumferential direction (for example, in  FIG. 2 , in two locations above and below); the number of locations installed may be appropriately set, and may be only one location. 
     Second Embodiment 
     The compressor system of the second embodiment is described next, with reference to  FIG. 4  to  FIG. 8 . 
     Constituent elements of the second embodiment which are equivalent to the first embodiment are given the same symbol and their detailed descriptions are omitted. The compressor system of the second embodiment is partially different from the first embodiment concerning the centrifugal separator. 
     A centrifugal separator  5 A of the second embodiment is provided on the upstream side of the compressor  2  as illustrated in  FIG. 4 . The centrifugal separator  5 A is formed larger than the outer diameter of the inlet of the first impeller  22  of the compressor  2 . The centrifugal separator  5 A rotates around the axis O with the motor  3  via the shaft  21 . This makes the centrifugal separator  5 A have a configuration which feeds out the externally supplied operating fluid toward the first impeller  22  while swirling it. 
     The centrifugal separator  5 A is provided as a separate body from the first impeller  22  of the compressor  2 , as illustrated in  FIG. 5 . The centrifugal separator  5 A is accommodated in a casing  6 A. The centrifugal separator  5 A is a separator provided with the second impeller  51  fixed on the outer peripheral surface of the shaft  21  of the compressor  2 , which extends in the direction of the axis O. 
     Note that the rotation shaft of the centrifugal separator  5 A is shared with the shaft  21  of the compressor  2 , but it may be provided as a separate body. 
     The second impeller  51  rotates with the shaft  21  around the axis O, and pressure-feeds the operating fluid flowing in from the direction of the axis O and passing through the interior of the second impeller  51  toward the outside of the direction of the axis O and the radial direction by centrifugal force. 
     The casing  6 A forms a cylindrical shape along the axis O, as illustrated in  FIG. 5 . The casing  6 A accommodates the compressor  2 , the motor  3 , and the centrifugal separator  5 A in its interior. The inner surface of the casing  6 A protrudes toward the shaft  21  between the compressor  2  and the motor  3  in the direction of the axis O. The protruding portion of the casing  6 A is provided with the seal member  60  which makes a seal between the region in which the compressor  2  is provided, the region in which the centrifugal separator  5  is provided, and the region in which the motor  3  is provided. 
     The casing  6 A sections off an inflow channel  61 , a first accommodation space  62 , a second accommodation space  63 , a foreign substance expulsion channel  64 A, and a foreign substance collection chamber  65 A. The inflow channel  61  guides the operation fluid from the exterior to the centrifugal separator  5 A. The first accommodation space  62  is disposed on the downstream side of the inlet channel  61  and accommodates the centrifugal separator  5 A. The second accommodation space  63  is connected on the downstream side of the first accommodation space  62 , and accommodates the first impeller  22  of the compressor  2 . The foreign substance expulsion channel  64 A extends radially outward from the first accommodation space  62  and expels the foreign substance in the operating fluid guided to the outer peripheral side by the centrifugal separator  5 A. The foreign substance collection chamber  65 A is connected to the foreign substance expulsion channel  64 A. 
     The first accommodation space  62  connects on with the inflow channel  61  one end side. The first accommodation space  62  connects with the second accommodation space  63  on the other end side. The first accommodation space  62  takes in the external operating fluid from the inflow channel  61 . The first accommodation space  62  is an interior space formed in the casing  6 A which rotatably accommodates the second impeller  51  of the centrifugal separator  5 A. 
     The foreign substance expulsion channel  64 A is attached in the central part of the axial direction of the first accommodation space  62 . The foreign substance expulsion channel  64 A is disposed at one location (the upper side on the paper surface) in the circumferential direction around the axis O, as illustrated in  FIG. 6 . The foreign substance expulsion channel  64 A forms a hole shape, and the channel cross section has the same cross section from its inlet to its outlet. 
     The foreign substance collection chamber  65 A is formed in the casing  6 A. The foreign substance collection chamber  65 A extends over the entire periphery along the circumferential direction around the axis O. The foreign substance collection chamber  65 A connects to the downstream side end part (an outlet  64   b ) of the foreign substance expulsion channel  64 A. 
     Note that the foreign substance expulsion channel  64 A has a configuration such that its entire circumferential direction does not connect to the first accommodation space  62 . Because of this, the foreign substance expulsion channel  64 A has a configuration which, when the operating fluid which has differing pressure in the circumferential direction flows into the same foreign substance collection chamber  65 A, can mitigate the return of the collected operating fluid from the foreign substance collection chamber  65 A into the first accommodation space  62  due to the differing pressure. 
     The operation of the compressor system  1  of the configuration described above is described next in detail, with reference to the drawings. 
     As illustrated in  FIG. 1 , according to the compressor system  1  such as that described above, the stator  32  is supplied with electric current via an external device such as an electric generator, which is not illustrated. A rotating magnetic field is generated based on the supplied electric current, and the rotor  31  of the motor  3  starts to rotate with the shaft  21 . As the shaft  21  rotates with high speed, as illustrated in  FIG. 5 , operating fluid is supplied from the exterior via the inflow channel  61  to the first accommodation space  62 . The operating fluid is accommodated in the first accommodation space  62  and swirled by the centrifugal separator  5 A, which rotates around the axis O via the motor  3 . The swirled operating fluid is fed out toward the first impeller  22  of the compressor  2  disposed on the downstream side of the centrifugal separator  5 A. At this time, in the first accommodation space  62 , foreign substances with large mass in the operating fluid are guided radially outward by the centrifugal force which is generated by the centrifugal separator  5 A. 
     The foreign substance in the operating fluid guided radially outward by the centrifugal separator  5 A flows into the foreign substance expulsion channel  64 A which extends radially outward from the first accommodation space  62 , is expelled, and collected. 
     The other operating fluid, which has smaller mass than the foreign substance which has flowed into the foreign substance expulsion channel  64 A, is fed out in the direction of the axis O and is made to flow into the first impeller  22  of the compressor  2 , which is on the downstream side of the centrifugal separator  5 A, and is then pressure-fed radially outward by the rotation of the first impeller  22 . This causes the foreign substance contained in the operating fluid to be separated on the upstream side of the first impeller  22 . Thus, it becomes possible to mitigate the mixing of foreign substance into the first impeller  22 , and prevent damage to the first impeller  22 . 
     In this manner, the second embodiment is a configuration such that the foreign substance expulsion channel  64 A is connected so it extends outward in the radial direction of the first accommodation space  62 . The foreign substance expulsion channel  64 A is a smooth channel along the direction of the axis O and is formed so that there is no ridge or the like in the first accommodation space  62 , and at the connection portion between the first accommodation space  62  and the second accommodation space  63 . This inhibits the occurrence of turbulent flow, and allows the foreign substances guided radially outward by centrifugal force to be efficiently collected. Because of this, when, for example, a liquid is mixed in a fluid which is mainly a gas, the liquid can be guided radially outward by the centrifugal force of the centrifugal separator  5 A and collected by the foreign substance expulsion channel  64 A. This imparts the function of gas-liquid separation. 
     Thus, when the operating fluid is a production fluid, which is a mix of crude oil, natural gas, and the like, and is retrieved by a subsea production system as in the first embodiment, gas-liquid separation can be done efficiently, and a superior effect can be exhibited. 
     In the second embodiment, the configuration has the foreign substance expulsion channel  64 A in one location, but the foreign substance collection chamber  65 A extend over the entire periphery of the circumferential direction. Because of this, if a plurality of foreign substance expulsion channels  64 A are disposed relative to one foreign substance collection chamber  65 A, foreign substance expelled from a plurality of locations can be efficiently gathered and collected in one foreign substance collection chamber  65 A. 
     The compressor system according to the second embodiment described above makes it possible to mitigate the mixing of foreign substance into the first impeller  22  of the compressor  2 , and to prevent damage to the first impeller  22 , by efficiently separating the foreign substance in the operating fluid. 
     An embodiment of the compressor system according to the present invention has been described but the present invention is not limited to the aforementioned second embodiment, and may be changed as appropriate in a range that does not deviate from the main intent thereof. 
     For example, in the second embodiment, the configuration was such that the foreign substance expulsion channel  64 A was connected in the center part of the first accommodation space  62  in the direction of the axis O, but the connection position in the direction of the axis O is not limited to this. For example, it may be a position near the inlet channel  61  on the upstream side of the first accommodation space  62  in the direction of the axis O, or a position near the second accommodation space  63  on the downstream side. 
     As in a first modification illustrated in  FIG. 7 , it may be a configuration such that a plurality (in  FIG. 7 , three locations in the upper region) of foreign substance expulsion channels  64 A are provided in the circumferential direction, where these foreign substance expulsion channels  64 A are disposed in a pressure region T (the two-point chain line illustrated in  FIG. 7 ) which makes the pressure of the operating fluid equal in the circumferential direction of the first accommodation space  62 . 
     In this case, fluid (foreign substance) of an equal pressure can be made to flow into the plurality of foreign substance expulsion channels  64 A disposed along the circumferential direction. This allows the pressure balance of the operating fluid in the first accommodation space  62  to be stabilized, and can prevent the foreign substance that has flowed into the foreign substance expulsion channel  64 A from returning to the first accommodation space  62 . 
     A second modification, which is illustrated in  FIG. 8 , has a configuration such that in the casing  6 A, a plurality (here, two locations) of foreign substance expulsion channels  64 A are provided along the direction of the axis O of the first accommodation space  62 . A foreign substance collection chamber  65 A is provided extending along the circumferential direction relative to each foreign substance expulsion channel  64 A. 
     In this case, the operating fluid (foreign substance) guided radially outward by centrifugal force from the centrifugal separator  5 A can be collected gradually by the foreign substance expulsion channels  64 A,  64 A in two locations along the direction of the axis O of the first accommodation space  62 , thereby allowing improvement of the gas-liquid separation function. 
     Note that in this case, in order to prevent foreign substance expulsion channels  64 A,  64 A which are next to each other in the direction of the axis O from connecting with each other via the centrifugal separator  5 A, the pitch in the direction of the axis O between the foreign substance expulsion channels  64  should be matched to the pitch of the second impeller  51  of the centrifugal separator  5 A. 
     In the first embodiment and the second embodiment, configurations for the shape of the second impeller  51  of the centrifugal separators  5 ,  5 A; the cross-sectional area and extension length of the foreign substance expulsion channels  64 ,  64 A; and the cross-sectional shape of the foreign substance collection chambers  65 ,  65 A and the like may be set as appropriate. 
     In the first embodiment and the second embodiment, the foreign substance collection chamber  65 ,  65 A had a configuration such that it extended along the entire periphery of the circumferential direction, but it may be provided on one part of the circumferential direction. 
     Third Embodiment 
     The attachment structure for a centrifugal separator of the third embodiment is described next, with reference to  FIGS. 9 and 10 . 
     In the third embodiment, constituent elements which are equivalent to those of the first embodiment and the second embodiment are given the same symbol and their detailed descriptions are omitted. The compressor system of the third embodiment is partially different from the first embodiment concerning the centrifugal separator. 
     The centrifugal separator  5 B of the third embodiment is provided on the upstream side of the compressor  2 , as illustrated in  FIG. 9 . The centrifugal separator  5 B is formed larger than the outer diameter of the inlet of the first impeller  22  of the compressor  2 . The centrifugal separator  5 B rotates around the axis O with the motor  3  via the shaft  21 . This makes the centrifugal separator  5 B have a configuration which feeds out the externally supplied operating fluid toward the first impeller  22  while swirling it. 
     As illustrated in  FIG. 10 , the centrifugal separator  5 B is provided as a separate body from the first impeller  22  of the compressor  2 . The centrifugal separator  5 B is accommodated in a casing  6 B. The centrifugal separator  5 B is a separator provided with a second impeller  51  fixed on the outer peripheral surface of the shaft  21  of the compressor  2 , which extends in the direction of the axis O. 
     Note that the rotation shaft of the centrifugal separator  5 B is shared with the shaft  21  of the compressor  2 , but it may be provided as a separate body. Here, as necessary, the portion of the shaft  21  to which the centrifugal separator  5 B attaches is called a rotation shaft  21 A in the description below. 
     The second impeller  51  rotates around the axis O with the shaft  21  (rotation shaft  21 A), and pressure-feeds the operating fluid, which flows in from the direction of the axis O and passes through the interior of the second impeller  51 , in the direction of the axis O and radially outward by centrifugal force. 
     The casing  6 B forms a cylindrical shape along the axis O, as illustrated in  FIG. 10 . The casing  6 B accommodates the compressor  2 , the motor  3 , and the centrifugal separator  5 B in its interior. The inner surface of the casing  6 B protrudes toward the shaft  21  between the compressor  2  and the motor  3  in the direction of the axis O. The protruding portion of the casing  6 B is provided with the seal member  60  which makes a seal between the region in which the compressor  2  is provided, the region in which the centrifugal separator  5 B is provided, and the region in which the motor  3  is provided. 
     The casing  6 B sections off an inflow channel  61 , a first accommodation space  62 , a second accommodation space  63 , a foreign substance expulsion channel  64 B, and a foreign substance collection chamber  65 B. The inflow channel  61  guides the operating fluid from the exterior to the centrifugal separator  5 B. The first accommodation space  62  is disposed on the downstream side of the inlet channel  61  and accommodates the centrifugal separator  5 . The second accommodation space  63  is connected on the downstream side of the first accommodation space  62 , and accommodates the first impeller  22  of the compressor  2 . The foreign substance expulsion channel  64 B extends radially outward from the first accommodation space  62  and expels the foreign substance in the operating fluid guided to the outer peripheral side by the centrifugal separator  5 B. The foreign substance collection chamber  65 B is connected to the foreign substance expulsion channel  64 B. 
     The first accommodation space  62  connects with the inflow channel  61  on one end side. The first accommodation space  62  connects with the second accommodation space  63  on the other end side. The first accommodation space  62  takes in the external operating fluid from the inflow channel  61 . The first accommodation space  62  is an interior space formed in the casing  6 B which rotatably accommodates the second impeller  51  of the centrifugal separator  5 B. 
     The foreign substance expulsion channel  64 B is attached to the center part of the first accommodation space  62  in the axial direction. The foreign substance expulsion channel  64 B is disposed in one location (the upper side on the paper surface) in the circumferential direction around the axis O. The foreign substance expulsion channel  64 B forms a hole shape, and the channel cross section has the same cross section from its inlet to its outlet. 
     The foreign substance collection chamber  65 B is formed in the casing  6 B. The foreign substance collection chamber  65 B extends over the entire periphery along the circumferential direction around the axis O. The foreign substance collection chamber  65 B has connected thereto the end part on the downstream side of the foreign substance expulsion channel  64 B. 
     The centrifugal separator  5 B is provided with a protruding part  53  and a protruding part  54 , which protrude toward both sides in the direction of the axis O from a base  52 , on the rotation shaft  21 A side. The protruding part  53  and the protruding part  54  are provided in a flange shape over the entire periphery of the circumferential direction. Of the protruding parts, the first protruding part  53  is pressed from the outer peripheral side by the holding recessed part  21   b  provided on the rotation shaft  21 A. The other, the second protruding part  54 , is pressed from the outer peripheral side by a fitting nut  7  (fitting member) which is attachable and removable relative to the rotation shaft  21 A. 
     Here, the rotation shaft  21 A of the shaft  21  is formed with a smaller diameter than the other portions of the shaft  21  (the holding part  21 B illustrated in  FIG. 10 ). A ridge is formed on the connecting portion between the rotation shaft  21 A and the holding part  21 B. The holding recessed part  21   b  opens toward the upstream side (toward the centrifugal separator  5 B side) in the direction of the axis O on this ridge. The holding recessed part  21   b  is formed over the entire periphery of the circumferential direction. 
     The fitting nut  7  is provided with a female screw  71  and a fitting recessed part  72 . The female screw  71  is provided on the same axis as the rotation shaft  21 A. The female screw  71  is formed on the outer peripheral surface of the rotation shaft  21 A. The fitting recessed part  72  fits from the outer peripheral side relative to the second protruding part  54 . When rotated around the axis O and tightened, the fitting nut  7  moves from the upstream side to the downstream side in the direction of the arrow E 1 , and is made so the fitting recessed part  72  fits on the outer peripheral side of the second protruding part  54  of the centrifugal separator  5 B. 
     An inner peripheral surface  72   a  of the fitting recessed part  72  forms a tapered surface. The tapered surface progressively expands radially outward from the upstream side to the downstream side. By having a taper surface in this manner, the inner peripheral surface  72   a  of the fitting recessed part  72  fits with the outer peripheral surface  54   a  of the second protruding part  54  in a state of being in close contact. 
     The operation of the attachment structure for a centrifugal separator with the configuration described above is described in detail next, with reference to drawings. 
     As illustrated in  FIG. 10 , according to the attachment structure for the centrifugal separator  5 B, the centrifugal separator  5 B is attached to the rotation shaft  21 A. At this time, the first protruding part  53  and the second protruding part  54  which protrude on both sides in the direction of the axis O from the base  52  of the centrifugal separator  5 B are in a state such that they are pressed down by the holding part  21 B of the shaft  21  and the fitting nut  7 , respectively, from the outer peripheral side. In other words, the base  52  of the centrifugal separator  5 B is pressed in the direction opposite the centrifugal force acting radially outward. As a result, the resistance against the centrifugal force is increased. 
     The fitting nut  7  which presses, the other, the second protruding part  54 , from the outer peripheral side is attachable and removable relative to the rotation shaft  21 A. Because of this, the fitting of the fitting nut  7  relative to the rotation shaft  21 A can be freed by moving the fitting nut  7  toward the upstream side (in the direction of the arrow E 2 ) by rotating in the direction the screw loosens (in the direction of the arrow E 2 ). This allows the pressing on the second protruding part  54  to be released, and the centrifugal separator  5 B to be easily separated from the rotation shaft  21 A. 
     In this manner, it becomes possible to improve the work efficiency for attaching and removing the centrifugal separator  5 B. Because of this, it is possible to efficiently exchange or perform maintenance such as cleaning for the centrifugal separator  5 B. 
     With the attachment structure for a centrifugal separator according to the third embodiment described above, by simply performing the attachment and removal work, work efficiency can be improved, and furthermore, resistance against the centrifugal force can be improved. 
     An embodiment of an attachment structure for a centrifugal separator according to the present invention has been described but the present invention is not limited to the aforementioned third embodiment, and may be changed as appropriate in a range that does not deviate from the main intent thereof. 
     For example, in the third embodiment, the holding part provided as one body on the rotation shaft  21 A is the target of the holding part  21 B, which is a part of the shaft  21 . However, the holding part is not limited to being these parts. For example, the holding part may be the rotor  31 , acting as the holding part provided as one body on the rotation shaft  21 A. In this case, the first protruding part  53  can be pressed on its entire periphery by the rotor  31 , which can secure stability and high strength. 
     In the third embodiment, the position at which the fitting member (fitting nut  7 ) fits is on the upstream side of the centrifugal separator  5 B, in the direction of the axis O. However, the protruding part on the downstream side may be pressed and fitted from the outer peripheral side by the fitting member, and the protruding part on the upstream side may be pressed by a holding part provided as one body on the rotation shaft  21 A. 
     The centrifugal separator  5 B may be divided in the circumferential direction. In this case, by freeing the fitting of the fitting member relative to the second protruding part  54 , the centrifugal separator  5 B, which has been divided in the circumferential direction, can be removed from the rotation shaft  21 A. In other words, the centrifugal separator  5 B can be exchanged without performing the work to release the rotor  31  connected to the rotation shaft  21 A from the shaft  21 . In particular, when the fitting member is a nut-style fitting nut  7  as described above, the work to completely remove the fitting member from the rotation shaft becomes unnecessary. 
     As for the fitting member, it is not limited to the shape nor dimensions of the fitting nut  7  such as that of the present embodiment, but other shapes and modes may be utilized. 
     Configurations such as the shape, size, position, and quantity for the centrifugal separator  5 B, the foreign substance expulsion channel  64 B, the foreign substance collection chamber  65 B, and the like may be set as appropriate. 
     On the other hand, within a range that does not deviate from the intent of the present invention, the constituent elements of the embodiments described above may be replaced as appropriate with known constituent elements, and the embodiments described above may be combined as appropriate. 
     INDUSTRIAL APPLICABILITY 
     According to the compressor system described above, mixing of foreign substance into an impeller can be mitigated, and damage to the impeller can be prevented by efficiently separating foreign substances in a fluid. 
     According to the attachment structure for a centrifugal separator described above, by simply performing attachment and removal work, work efficiency can be improved, and furthermore, resistance against the centrifugal force can be improved. 
     REFERENCE SIGNS LIST 
     
         
           1  Compressor system 
         O Shaft line 
           2  Compressor 
           21  Shaft 
           21 A Rotation shaft 
           21 B Holding part 
           21   b  Recessed holding part 
           21   c  Male screw 
           22  First impeller 
           23  Housing 
           3  Motor 
           31  Rotor 
           32  Stator 
           33  Gap 
           4  Bearing 
           41  Journal bearing 
           42  Thrust bearing 
           5 ,  5 A,  5 B Centrifugal separator 
           51  Second impeller 
           52  Base 
           53  First protruding part 
           54  Second protruding part 
           6 ,  6 A,  6  Casing 
           60  Sealing member 
           61  Inflow channel 
           62  First accommodation space 
           63  Second accommodation space 
           64 ,  64 A,  64 B Foreign substance expulsion channel 
           65 ,  65 A,  65 B Foreign substance collection chamber 
         T Pressure region 
           7  Fitting nut 
           71  Female screw 
           72  Fitting recessed part