Pump device

Abstract

A pump device (1) according to the present disclosure comprises: a rotary shaft (21) that is centered on an axis extending in the vertical direction; an upper radial bearing (41a) that supports an upper portion of the rotary shaft to be rotatable around the axis; a lower radial bearing (41b) that supports a lower portion of the rotary shaft to be rotatable around the axis; a first seal mechanism (4) that is provided between the upper radial bearing and the lower radial bearing; an electric motor (50), between the upper radial bearing and the first seal mechanism, that drives the rotary shaft to rotate around the axis; a plurality of impellers (55) that are provided below the first seal mechanism, and pump low-viscosity, low-temperature fluid from downward to upward; and a second seal mechanism (5) that is provided between the lower radial bearing and the first seal mechanism. The plurality of impellers include a pair of impellers mounted back-to-back, and the second seal mechanism is installed at the mounting position of the pair of impellers mounted back-to-back.

Description

Pump equipment

[0001] This application claims priority to Japanese Patent Application No. 2024-152208, filed on September 4, 2024, the contents of which are incorporated herein by reference.

[0002] Patent Document 1 discloses a pump for pumping a low-viscosity cryogenic fluid. This pump includes a pump section for increasing the pressure of the fluid and a motor section for driving the pump section.

[0003] Japanese Patent Application Laid-Open No. 2005-105897

[0004] When a pump pumps high pressure and large flow rate, the flow of low-viscosity cryogenic fluid causes the rotating shaft to vibrate significantly, which has been an issue.

[0005] The present disclosure provides a pump device that can suppress vibrations even when pumping a low-viscosity cryogenic fluid at high pressure and large flow rate.

[0006] In order to solve the above-described problems, a pump device according to the present disclosure includes a rotating shaft centered on an axis extending in a vertical direction, an upper radial bearing supporting an upper part of the rotating shaft rotatably about the axis, a lower radial bearing supporting a lower part of the rotating shaft rotatably about the axis, a first seal mechanism provided between the upper radial bearing and the lower radial bearing and through which the rotating shaft is inserted, an electric motor that drives the rotating shaft to rotate about the axis between the upper radial bearing and the first seal mechanism, a plurality of impellers provided below the first seal mechanism and that pressurize a low-viscosity cryogenic fluid from below to above as the rotating shaft rotates about the axis, and a second seal mechanism provided between the lower radial bearing and the first seal mechanism and through which the rotating shaft is inserted, wherein the plurality of impellers include a pair of impellers mounted back-to-back, and the second seal mechanism is provided at a mounting position of the pair of impellers mounted back-to-back.

[0007] According to the pump device of the present disclosure, vibrations can be suppressed even when pumping a low-viscosity cryogenic fluid at high pressure and large flow rate.

[0008] 1A and 1B are schematic configuration diagrams of a pump device according to a first embodiment of the present disclosure and a second embodiment of the present disclosure;

[0009] First Embodiment (Configuration of Pump Device) A pump device 1 according to a first embodiment of the present disclosure will be described below with reference to FIG. 1 . The pump device is a device that pressurizes a low-viscosity cryogenic fluid L. In this embodiment, the cryogenic fluid L is liquefied hydrogen. Note that the cryogenic fluid L pressurized by the pump device 1 is not limited to liquid hydrogen and may be other liquids or gases. For example, the cryogenic fluid L may be a liquefied gas other than liquid hydrogen, such as natural gas (LNG) or liquefied petroleum gas (LPG). The pump device 1 pumps the cryogenic fluid L at a pressure of 0.5 to 3.0 MPa and a flow rate of 1.5 to 10.0 t / h. As shown in FIG. 1 , the pump device 1 includes a sump 10 and a cryogenic fluid pump 20.

[0010] (Sump) The sump 10 stores the cryogenic fluid L (liquid hydrogen in this embodiment). The sump 10 is a vacuum insulated container. That is, the sump 10 is a thermally insulated structure having a cylindrical shape with a bottom. The sump 10 is installed on a stand (not shown). The sump 10 has a sump body 11, an outer peripheral flange 12, an upper flange 13, and a mounting wall 14. The sump body 11 is formed in a cylindrical shape with a bottom that opens upward. A liquid storage chamber 15 is formed inside the sump body 11. The liquid storage chamber 15 stores the cryogenic fluid L. A supply pipe 2 and a gas discharge pipe 3 are connected to the side of the sump body 11. The supply pipe 2 is a pipe that can supply the cryogenic fluid L from an external supply source into the liquid storage chamber 15. The gas discharge pipe 3 is a pipe capable of discharging the gas component of the low-temperature fluid L vaporized in the liquid storage chamber 15 to the outside of the sump 10. The gas discharge pipe 3 is provided vertically above the supply pipe 2. The gas discharge pipe 3 may also be capable of discharging the liquid component of the low-temperature fluid L to the outside of the sump 10.

[0011] The outer peripheral flange 12 is provided on the upper side of the sump body 11 and protrudes from the outer peripheral surface of the sump body 11. The upper flange 13 is attached to the upper part of the sump body 11. The upper flange 13 closes the opening of the sump body 11. The upper flange 13 is attached so as to contact the outer peripheral flange 12 from above and maintain airtightness inside the liquid storage chamber 15. The mounting wall portion 14 is attached to the underside of the upper flange 13. The mounting wall portion 14 is a flat member extending horizontally.

[0012] (Cryogenic Fluid Pump) The cryogenic fluid pump 20 is a device that pressurizes the cryogenic fluid L (liquid hydrogen in this embodiment) to a target pressure and pumps it. The cryogenic fluid pump 20 is disposed in the sump 10. The cryogenic fluid pump 20 of this embodiment includes a rotating shaft 21, a casing 30, a bearing device 40, an electric motor 50, a first seal mechanism 4, a first outer seal unit 7, an impeller 55, a second seal mechanism 5, a second outer seal unit 8, an inducer 6, and a cryogenic fluid flow path 60.

[0013] (Rotation shaft) The rotation shaft 21 is centered on an axis O extending in the vertical direction Dv. One side of the axis O is the lower side Dvd, and the other side of the axis O is the upper side Dvu. In addition, the circumferential direction about this axis O will be simply referred to as the circumferential direction, and the radial direction about this axis O will be simply referred to as the radial direction in this description. The rotation shaft 21 is provided so as to be rotatable around this axis O.

[0014] (Casing) The casing 30 forms the outer shell of the cryogenic fluid pump 20. The casing 30 is hollow. The casing 30 is suspended from the upper flange 13 via the mounting wall 14. The casing 30 has a cylindrical shape centered on an axis O extending along the vertical direction, but is not limited to this. Although the sump 10 and the casing 30 both extend about the axis O, the centers of the sump 10 and the casing 30 may be offset from each other. The casing 30 accommodates the components of the cryogenic fluid pump 20, such as the rotating shaft 21, the bearing device 40, the electric motor 50, the first seal mechanism 4, the first outer seal 7, the impeller 55, the second seal mechanism 5, the second outer seal 8, and the inducer 6. The casing 30 may be constructed from a single member or may be constructed by assembling multiple members together.

[0015] In this embodiment, the casing 30 includes a motor casing 31, a pump casing 32, and a flange portion 33. The motor casing 31 is formed in a cylindrical shape with a bottom that opens downward. The pump casing 32 is disposed below the motor casing 31. The pump casing 32 is formed in a cylindrical shape with a bottom that opens upward. The flange portion 33 includes an upper flange 33a provided at the lower end of the motor casing 31 and a lower flange 33b provided at the upper end of the pump casing 32. The upper flange 33a protrudes radially outward from the outer peripheral surface of the motor casing 31. The upper flange 33a is formed integrally with the motor casing 31. The lower flange 33b protrudes radially outward from the outer peripheral surface of the pump casing 32. The lower flange 33b is formed integrally with the pump casing 32. The lower flange 33b contacts the upper flange 33a and is fixed to the upper flange 33a by, for example, bolts (not shown). The flange portion 33 firmly assembles the motor casing 31 and the pump casing 32 together.

[0016] A suction section 34 is provided at the lower end of the pump casing 32. The suction section 34 opens downward. The cryogenic fluid L stored in the liquid storage chamber 15 of the sump 10 is sucked into the casing 30 through the suction section 34. The suction section 34 may be directly connected to the supply pipe 2 or another pipe extended from the supply pipe 2. In other words, the cryogenic fluid L may be introduced directly into the suction section 34 from a pipe without first being stored in the liquid storage chamber 15 of the sump 10.

[0017] An upper accommodating chamber 35 is formed at the upper end of the motor casing 31. The upper end of the rotating shaft 21 is accommodated in the upper accommodating chamber 35. The upper accommodating chamber 35 is capable of receiving the cryogenic fluid L that flows upward along the rotating shaft.

[0018] (Bearing Device) The bearing device 40 is a device that supports the rotating shaft 21 so that the rotating shaft 21 can rotate about the axis O. The bearing device 40 includes a radial bearing 41, a thrust disk 42, and a thrust bearing 43.

[0019] (Radial Bearing) The radial bearing 41 is arranged to receive a radial load from the rotating shaft 21. That is, the radial bearing 41 is arranged concentrically with the rotating shaft 21 and is arranged to cover the outer circumferential surface of the rotating shaft 21. A plurality of radial bearings 41 are provided. In this embodiment, an upper radial bearing 41a and a lower radial bearing 41b are provided. The upper radial bearing 41a is arranged vertically above the casing 30. The upper radial bearing 41a supports the upper part of the rotating shaft 21 rotatably around the axis O. The lower radial bearing 41b is arranged vertically below the casing 30. The lower radial bearing 41b supports the lower part of the rotating shaft rotatably around the axis O. The type of the radial bearing 41 is not limited. For example, the radial bearing 41 may be a rolling bearing, a sliding bearing, or a magnetic bearing. The upper radial bearing 41 a and the lower radial bearing 41 b may be the same type of bearing or may be different types of bearing. In the following, an embodiment will be described taking as an example a case where the upper radial bearing 41 a and the lower radial bearing 41 b are both magnetic bearings.

[0020] (Thrust Disk) The thrust disk 42 is fixed to the outer periphery of the rotating shaft 21. The thrust disk 42 is circular and is provided so as to expand the diameter of the rotating shaft 21 in the radial direction while fixed to the rotating shaft 21. The thrust disk 42 is rotatable integrally with the rotating shaft 21. The thrust disk 42 is also movable integrally with the rotating shaft 21 in the direction of the axis O.

[0021] (Thrust Bearing) The thrust bearing 43 is arranged to sandwich the thrust disk 42 in the direction of the axis O. The thrust bearing 43 in this embodiment is a hydrostatic bearing. The thrust bearing 43 is, for example, a non-contact bearing. For example, the thrust bearing 43 may be a magnetic bearing. However, the thrust bearing 43 is not limited to a non-contact bearing. Furthermore, the thrust bearing 43 is arranged vertically above the upper radial bearing 41 a and the lower radial bearing 41 b.

[0022] (First Seal Mechanism) The first seal mechanism 4 is, for example, a seal mechanism called a balance sleeve. The first seal mechanism 4 is disposed between the upper radial bearing 41a and the lower radial bearing 41b in the axial direction O. The first seal mechanism 4 is formed in a disk shape centered on the axial direction O, and the rotating shaft 21 is inserted through the first seal mechanism 4. The first seal mechanism 4 is disposed at the same position in the axial direction O as the flange portion 33 of the casing 30, i.e., at a position radially overlapping with the flange portion 33 of the casing 30. The first seal mechanism 4 is formed in a flange shape extending from the rotating shaft 21. The first seal mechanism 4 divides the space within the casing 30 in the up-down direction Dv. The first seal mechanism 4 is covered from the radial outside by the first outer seal portion 7. A gap is provided between the outer peripheral surface of the first seal mechanism 4 and the inner peripheral surface of the first outer seal portion 7, sufficient to allow the flow of the cryogenic fluid L while generating a pressure difference between above and below the first seal mechanism 4. The pressure in the space above the first seal mechanism 4 is lower than the pressure in the space below the first seal mechanism 4. Therefore, a thrust force acts on the first seal mechanism 4 in the direction of the axis O from below. The first seal mechanism 4 adjusts this thrust force from below to above. Furthermore, within the casing 30, the pressure in the space above the first seal mechanism 4 gradually decreases as it goes upward, but the pressure is approximately the same from the first seal mechanism 4 to the upper accommodating chamber 35. The pressure within the upper accommodating chamber 35 is kept at an intermediate pressure approximately the same as that of the second-stage impeller 55b to the third-stage impeller 55c by the balance piping 65 described below.

[0023] (Electric Motor) The electric motor 50 drives the rotating shaft 21 to rotate around the axis O between the upper radial bearing 41a and the first seal mechanism 4 in the direction of the axis O. The electric motor 50 has a stator 51 and a rotor 52. The stator 51 is fitted to the inner circumferential surface of the casing 30. The stator 51 is cylindrical and has a stator core and a stator coil. The rotor 52 is fixed integrally to the rotating shaft 21 inside the stator 51. The rotor 52 is cylindrical and has a rotor core (e.g., a permanent magnet or laminated steel plates). The stator 51 fixed to the casing 30 and the rotor 52 fixed to the rotating shaft 21 face each other in the radial direction with a gap between them.

[0024] (Impeller) A plurality of impellers 55 are provided below the first seal mechanism 4. The plurality of impellers 55 pressure-feed the cryogenic fluid L from below to above as the rotary shaft 21 rotates about the axis O. The plurality of impellers 55 includes a pair of impellers 55 attached back to back. In this embodiment, the lower radial bearing 41b is provided between two adjacent impellers 55. Note that the number of impellers 55 can be changed as appropriate, but in this embodiment, a case where five stages of impellers 55 are provided will be described.

[0025] The multiple impellers 55 compress and feed the low-pressure fluid L drawn into the casing 30 from the suction section 34 in stages. Hereinafter, the five impellers 55 will be referred to as the first-stage impeller 55a, the second-stage impeller 55b, the third-stage impeller 55c, the fourth-stage impeller 55d, and the fifth-stage impeller 55e, in order from the low-pressure side. The first-stage impeller 55a may be described as the low-pressure impeller 55, the second-stage impeller 55b and the third-stage impeller 55c as the intermediate-pressure impellers 55, and the fourth-stage impeller 55d and the fifth-stage impeller 55e as the high-pressure impellers 55. The fifth-stage impeller 55e may also be described as the final-stage impeller 55.

[0026] The first-stage impeller 55a is disposed below the lower radial bearing 41b. The first-stage impeller 55a is disposed so as to pump the cryogenic fluid L upward. The second-stage impeller 55b to the fifth-stage impeller 55e are disposed between the lower radial bearing 41b and the first seal mechanism 4 in the direction of the axis O (in the up-down direction Dv). Arranged from bottom to top are the second-stage impeller 55b, the third-stage impeller 55c, the fifth-stage impeller 55e, and the fourth-stage impeller 55d. The second-stage impeller 55b and the third-stage impeller 55c are disposed so as to pump the cryogenic fluid L upward, while the fourth-stage impeller 55d and the fifth-stage impeller 55e are disposed so as to pump the cryogenic fluid L downward. The third-stage impeller 55c and the fifth-stage impeller 55e are disposed back-to-back to each other.

[0027] (Second Seal Mechanism) The second seal mechanism 5 is, for example, a seal mechanism called a center stage. The second seal mechanism 5 is provided between the lower radial bearing 41b and the first seal mechanism 4. The second seal mechanism 5 is formed in a cylindrical shape centered on the axis O, and the rotating shaft 21 is inserted through the second seal mechanism 5. The second seal mechanism 5 is provided at the mounting position of a pair of impellers (in this embodiment, a third-stage impeller 55c and a fifth-stage impeller 55e) mounted back-to-back. More specifically, the third-stage impeller 55c and the fifth-stage impeller 55e are fitted back-to-back on the outer circumferential surface of the second seal mechanism 5.

[0028] (Inducer) The inducer 6 is provided below the lower radial bearing 41b and the multiple impellers. The inducer 6 is disposed in the suction section 34 of the casing 30. The inducer 6 rotates integrally with the rotating shaft 21. The rotation of the inducer 6 causes the cryogenic fluid L to be sucked into the casing 30.

[0029] (Cryogenic Fluid Flow Path) The cryogenic fluid flow path 60 circulates the cryogenic fluid L. The cryogenic fluid flow path 60 has a main flow path 61, a discharge section 62, a discharge pipe 63, branch flow paths 64, and a balance pipe 65. The main flow path 61 is shown by a solid line, the branch flow paths 64 are shown by a dashed line, and the balance pipe 65 is shown by a two-dot chain line.

[0030] (Main Flow Passage) The main flow passage 61 circulates the cryogenic fluid L so that it passes through the multiple impellers 55. The main flow passage 61 has a first main flow passage 61a, a second main flow passage 61b, and a third main flow passage 61c. The first main flow passage 61a guides the low-pressure cryogenic fluid L pressurized by the first-stage impeller 55a to the second-stage impeller 55b. The first main flow passage 61a is formed, for example, within the casing 30. The first main flow passage 61a connects the first-stage impeller 55a and the second-stage impeller 55b so as to bypass the lower radial bearing 41b. The second main flow passage 61b guides the intermediate-pressure cryogenic fluid L pressurized by the second-stage impeller 55b and the third-stage impeller 55c to the fourth-stage impeller 55d. The second main flow passage 61b is formed, for example, within the casing 30. The third main flow path 61c guides the high-pressure low-temperature fluid L pressurized by the fourth-stage impeller 55d and the fifth-stage impeller 55e to a discharge section 62 (described later). The third main flow path 61c is, for example, a pipe arranged at a position radially outwardly spaced from the outer circumferential surface of the casing 30. The third main flow path 61c may be provided inside the casing 30.

[0031] (Discharge Portion) The discharge portion 62 is formed on the lower surface of the upper flange 13. When viewed from below, the discharge portion 62 is formed in a circular shape centered on the axis O. The discharge portion 62 is supplied with high-pressure cryogenic fluid L pressurized by the multiple impellers 55.

[0032] (Discharge Pipe) The discharge pipe 63 extends upward from the center of the discharge portion 62. The discharge pipe 63 discharges the low-temperature fluid L in the discharge portion 62 to the outside.

[0033] (Branch Flow Path) The branch flow path 64 branches off from the main flow path 61 and allows the cryogenic fluid L to flow through the upper radial bearing 41a, the lower radial bearing 41b, the electric motor 50, and the thrust bearing 43. In this embodiment, the branch flow path 64 includes a first branch flow path 64a, a second branch flow path 64b, and a third branch flow path 64c. The first branch flow path 64a supplies a portion of the cryogenic fluid L supplied from the first-stage impeller 55a to the second-stage impeller 55b to the lower radial bearing 41b. In this embodiment, the first branch flow path 64a is formed so that the cryogenic fluid L passes from the second-stage impeller 55b through the lower radial bearing 41b and returns to the first main flow path 61a. The first branch flow path 64a is formed, for example, by a passage formed in the casing 30 or a gap between each component. The cryogenic fluid L supplied to the lower radial bearing 41b is returned to the first main flow path 61a. The second branch flow path 64b returns a portion of the cryogenic fluid L supplied from the fifth-stage impeller 55e to the discharge portion 62 to the third-stage impeller 55c. The second branch flow path 64b is configured, for example, by a passage formed in the casing 30 or by gaps between components. The third branch flow path 64c supplies a portion of the cryogenic fluid L supplied from the third-stage impeller 55c to the fourth-stage impeller 55d to the upper first seal mechanism 4, the electric motor 50, the upper radial bearing 41a, and the thrust bearing 43. The cryogenic fluid L that has passed through the thrust bearing 43 is temporarily stored in the upper storage chamber 35. The third branch flow path 64c is configured, for example, by a passage formed in the casing 30 or by gaps between components. In this embodiment, the third branch flow path 64c is a gap between components in the casing 30, and the upstream end of the third branch flow path 64c is the gap between the first seal mechanism 4 and the first outer seal unit 7.

[0034] (Balance Piping) The balance piping 65 returns the low-temperature fluid L that has passed through the upper radial bearing 41 a, the electric motor 50, and the thrust bearing 43 to the intermediate-pressure impeller 55 (in this embodiment, between the second-stage impeller 55 b and the third-stage impeller 55 c) among the multiple impellers 55. The balance piping 65 connects the upper housing chamber 35 to the region between the second-stage impeller 55 b and the third-stage impeller 55 c in the casing 30, thereby reducing the pressure difference and suppressing the thrust force acting on the first seal mechanism 4 in the direction of the axis O. The balance piping 65 is, for example, a piping that is disposed at a position radially outward from the outer circumferential surface of the casing 30. Note that the balance piping 65 may also be provided inside the casing 30.

[0035] (Flow of Cryogenic Fluid) Next, a description will be given of the flow of the cryogenic fluid when the pump device 1 is in operation. As shown in Fig. 1, when the electric motor 50 is driven, the rotary shaft 21 is driven to rotate, and the impeller 5 and inducer 6 fixed to the rotary shaft 21 rotate. At this time, the radial bearing 41 bears a load on the rotary shaft 21 in a direction perpendicular to the rotary shaft 21 (radial direction). Furthermore, the thrust bearing 43 bears a load on the rotary shaft 21 in the direction of the axis O.

[0036] The cryogenic fluid L in the liquid storage chamber 15 is drawn into the suction section 34 by the inducer 6 and is pressurized in stages by the multiple impellers 55. The cryogenic fluid L drawn into the suction section 34 by the inducer 6 is pressurized by the first-stage impeller 55a. The cryogenic fluid L then passes through the first main flow path 61a and is sent to the second-stage impeller 55b. The cryogenic fluid L is further pressurized by the second-stage impeller 55b and the third-stage impeller 55c to become an intermediate-pressure cryogenic fluid L. Most of the intermediate-pressure cryogenic fluid L passes through the second main flow path 61b and is sent to the fourth-stage impeller 55d. At this time, a portion of the cryogenic fluid L passes through the first branch flow path 64a and is sent from the second-stage impeller 55b to the lower radial bearing 41b. This cryogenic fluid L has a cooling function as a lubricating liquid for the lower radial bearing 41b. The cryogenic fluid L supplied to the lower radial bearing 41b passes through the first branch flow path 64a and is returned to the first main flow path 61a. In this manner, a portion of the cryogenic fluid L circulates between the second-stage impeller 55b and the lower radial bearing 41b.

[0037] The cryogenic fluid L sent from the third-stage impeller 55c to the fourth-stage impeller 55d is further pressurized by the fourth-stage impeller 55d and the fifth-stage impeller 55e to become high-pressure cryogenic fluid L. Most of the high-pressure cryogenic fluid L is sent to the discharge section 62 through the third main flow path 61c and discharged to the outside of the pump device 1 through the discharge pipe. At this time, a portion of the cryogenic fluid L supplied from the fifth-stage impeller to the discharge section 62 is returned from the fifth-stage impeller 55e to the third-stage impeller 55c through the second branch flow path 64b. In addition, a portion of the cryogenic fluid L supplied to the fourth-stage impeller 55d is supplied through the third branch flow path 64c to the first seal mechanism 4 above, the electric motor 50, the upper radial bearing 41a, and the thrust bearing 43, in that order. This cryogenic fluid L has a cooling function as a lubricating liquid for the first seal mechanism 4, the electric motor 50, the upper radial bearing 41a, and the thrust bearing 43. The cryogenic fluid L supplied to the thrust bearing 43 is temporarily stored in the upper storage chamber 35. The cryogenic fluid L stored in the upper storage chamber 35 passes through the balance piping 65 and is returned to the intermediate-pressure impeller 55 (between the second-stage impeller 55b and the third-stage impeller 55c). This suppresses gasification of the cryogenic fluid L compared to when the cryogenic fluid L is returned to the lowest-pressure impeller 55. The cryogenic fluid L returned to the intermediate-pressure impeller 55 is again pressurized in stages by the intermediate-pressure impeller 55 and the high-pressure impeller 55.

[0038] (Operations and Effects) The pump device 1 configured as described above can achieve the following operations and effects. In this embodiment, the pump device 1 includes a rotating shaft 21, an upper radial bearing 41a, a lower radial bearing 41b, a first seal mechanism 4, an electric motor 50, multiple impellers 55, and a second seal mechanism 5. The rotating shaft 21 is centered on an axis O extending in the vertical direction. The upper radial bearing 41a supports an upper portion of the rotating shaft 21 rotatably about the axis O. The lower radial bearing 41b supports a lower portion of the rotating shaft 21 rotatably about the axis O. The first seal mechanism 4 is provided between the upper radial bearing 41a and the lower radial bearing 41b, and the rotating shaft 21 is inserted through the first seal mechanism 4. The electric motor 50 drives the rotating shaft 21 to rotate about the axis O between the upper radial bearing 41a and the first seal mechanism 4. The multiple impellers 55 are provided below the first seal mechanism 4, and pressure-feed the cryogenic fluid L from below upward as the rotating shaft 21 rotates about the axis O. The second seal mechanism 5 is provided between the lower radial bearing 41b and the first seal mechanism 4, and has the rotating shaft 21 inserted therethrough. Furthermore, the multiple impellers 55 include a pair of impellers 55 attached back to back, and the second seal mechanism 5 is provided at the attachment position of the pair of impellers 55 attached back to back.

[0039] According to the above-described configuration, both the upper and lower ends of the rotating shaft 21 are supported by the upper radial bearing 41a and the lower radial bearing 41b. This suppresses overall vibration of the rotating shaft 21. The electric motor 50 and impeller 55, which are vibration sources, are disposed between the upper radial bearing 41a and the lower radial bearing 41b, and the first seal mechanism 4 is disposed between the electric motor 50 and the impeller. The first seal mechanism 4 is, for example, a so-called balance sleeve. Furthermore, a second seal mechanism 5 is provided at the mounting position of the pair of impellers 55 mounted back-to-back. The second seal mechanism 5 is, for example, a so-called center stage. The first seal mechanism 4 and the second seal mechanism 5 damp the rotating shaft 21, further suppressing vibration of the rotating shaft 21. Therefore, the pump device 1 of this embodiment can suppress vibration even when pumping high-pressure, large-flow volumes. From another perspective, the first seal mechanism 4 functions as a heavy object disposed between the electric motor 50 and the impeller 55. This vibrationally decouples the electric motor 50 from the impeller 55. This prevents the vibrations of the electric motor 50 and the impeller 55 from adversely affecting each other, thereby suppressing vibrations of the pump device 1 as a whole.

[0040] In this embodiment, the lower radial bearing 41 b is provided between two adjacent impellers 55 .

[0041] The pump device 1 can supply the cryogenic fluid L pressure-fed by the impeller 55 to the lower radial bearing 41b. This allows the pump device 1 to lubricate the lower radial bearing 41b while cooling it. In particular, in this embodiment, the lower radial bearing 41b is disposed between the first-stage impeller 55a and the second-stage impeller 55b, and the first branch flow path 64a circulates the cryogenic fluid L between the first-stage impeller 55a and the lower radial bearing 41b. This allows the pump device 1 to cool and lubricate the lower radial bearing 41b with the cryogenic fluid L while suppressing the load on the lower radial bearing 41b.

[0042] In this embodiment, the pump device 1 includes an inducer 6 that is provided below the lower radial bearing 41b and the multiple impellers 55 and that draws in the low-temperature fluid L.

[0043] This prevents the suction of the cryogenic fluid L from being hindered by the lower radial bearing 41b or the impeller 55. Furthermore, vibrations caused by the suctioned cryogenic fluid L colliding with the lower radial bearing 41b or the impeller are suppressed. This allows the pump device 1 to smoothly suction the cryogenic fluid L.

[0044] In this embodiment, the pump device 1 pumps the low-temperature fluid L at a pressure of 0.5 to 3.0 MPa and a flow rate of 1.5 to 10.0 t / h.

[0045] When pumping the cryogenic fluid at a pressure of 0.5 to 3.0 MPa and a flow rate of 1.5 to 10.0 t / h, the pump device 1 can suitably suppress vibrations while pumping the cryogenic fluid at a high pressure and a large flow rate.

[0046] In this embodiment, the pump device 1 includes a thrust bearing 43 and a cryogenic fluid flow path 60. The cryogenic fluid flow path 60 has a main flow path 61, a branch flow path 64, and a balance pipe 65. The thrust bearing 43 is disposed above the upper radial bearing 41a. The cryogenic fluid flow path 60 circulates the cryogenic fluid L. The main flow path 161 circulates the cryogenic fluid L so that it passes through multiple impellers 55. The branch flow path 64 branches off from the main flow path 61 and circulates the cryogenic fluid L so that it passes through the upper radial bearing 41a, the lower radial bearing 41b, the electric motor 50, and the thrust bearing 43. The balance pipe 65 returns the cryogenic fluid L that has passed through the upper radial bearing 41a, the electric motor 50, and the thrust bearing 43 to the intermediate-pressure impeller 55 among the multiple impellers.

[0047] As a result, the flow of the cryogenic fluid L is branched from the impeller 55 and supplied to the upper radial bearing 41 a, the lower radial bearing 41 b, and the electric motor 50. The cryogenic fluid pump 20 can cool and lubricate the upper radial bearing 41 a, the lower radial bearing 41 b, and the electric motor 50 using this branched cryogenic fluid L. Furthermore, according to this embodiment, the cryogenic fluid pump 20 can return the cryogenic fluid L that has passed through the electric motor 50 and the upper radial bearing 41 a to the intermediate-pressure impeller 55 via the balance piping 165 and circulate it. Furthermore, the cryogenic fluid L is returned to the intermediate-pressure impeller 55. As a result, gasification of the cryogenic fluid L is suppressed compared to when the cryogenic fluid L is returned to the impeller 55 on the lowest-pressure side.

[0048] In this embodiment, the cryogenic fluid L is liquid hydrogen.

[0049] When the cryogenic fluid L is liquid hydrogen, the pump device 1 can effectively suppress vibrations while pumping the cryogenic fluid L at a high pressure and a large flow rate.

[0050] Second Embodiment (Configuration of Pump Device) A pump device 101 according to a second embodiment of the present disclosure will be described below with reference to Fig. 2. Components common to the first embodiment will be designated by the same names and reference numerals, and descriptions thereof will be omitted as appropriate. In the second embodiment, the radial bearing 41 is a hydrostatic bearing, and the configuration of the cryogenic fluid flow path 160 differs from that of the first embodiment.

[0051] (Cryogenic Fluid Flow Path) The cryogenic fluid flow path 160 has a main flow path 161, a discharge section 162, a discharge pipe 163, a branch flow path 164, and a balance pipe 165. The main flow path 161 is shown by a solid line, the branch flow path 164 is shown by a dashed line, and the balance pipe 165 is shown by a two-dot chain line.

[0052] (Main Flow Passage) The main flow passage 161 circulates the cryogenic fluid L so that it passes through the multiple impellers 55. The main flow passage 161 includes a first main flow passage 161a, a second main flow passage 161b, and a third main flow passage 161c. The first main flow passage 161a guides the low-pressure cryogenic fluid L pressurized by the first-stage impeller 55a to the second-stage impeller 55b. The first main flow passage 161a is formed, for example, within the casing 30. The first main flow passage 161a connects the first-stage impeller 55a and the second-stage impeller 55b so as to bypass the lower radial bearing 41b. The second main flow passage 161b guides the intermediate-pressure cryogenic fluid L pressurized by the second-stage impeller 55b and the third-stage impeller 55c to the fourth-stage impeller 55d. The second main flow passage 161b is formed, for example, within the casing 30. The third main flow path 161c guides the high-pressure low-temperature fluid L pressurized by the fourth-stage impeller 55d and the fifth-stage impeller 55e to a discharge portion 162 (described later). The third main flow path 161c is, for example, a pipe arranged radially outward from the outer circumferential surface of the casing 30. The third main flow path 161c may be provided inside the casing 30.

[0053] (Discharge Portion) The discharge portion 162 is formed on the lower surface of the upper flange. When viewed from below, the third flow path is formed in a circular shape centered on the axis O. The discharge portion 162 is supplied with the high-pressure cryogenic fluid L pressurized by the multiple impellers 55.

[0054] (Discharge Pipe) The discharge pipe 163 extends upward from the center of the discharge portion 162. The discharge pipe 163 discharges the low-temperature fluid L in the discharge portion 162 to the outside.

[0055] (Branch Flow Path) The branch flow path 164 branches off from the main flow path 161 and allows the cryogenic fluid L to pass through the upper radial bearing 41a, the lower radial bearing 41b, the electric motor 50, and the thrust bearing 43. In this embodiment, the branch flow path 164 includes a first branch flow path 164a, a second branch flow path 164b, a third branch flow path 164c, a fourth branch flow path 164d, and a fifth branch flow path 164e. The first branch flow path 164a supplies a portion of the cryogenic fluid L pressurized by the third-stage impeller 55c to the lower radial bearing 41b. The first branch flow path 164a is formed, for example, by a passage formed in the casing 30 or a gap between each component. The second branch flow path 164b returns a portion of the cryogenic fluid L supplied from the fifth-stage impeller to the discharge portion 162 to the third-stage impeller 55c. The second branch flow path 164b is configured, for example, by a passage formed within the casing 30 or a gap between each component. The third branch flow path 164c supplies a portion of the cryogenic fluid L supplied from the third-stage impeller 55c to the fourth-stage impeller 55d to the upper first seal mechanism 4 and the electric motor 50. The third branch flow path 164c mainly supplies the cryogenic fluid L to the electric motor 50. The third branch flow path 164c is configured, for example, by a passage formed within the casing 30 or a gap between each component. In this embodiment, the third branch flow path 164c is a gap between each component within the casing 30, and the upstream end of the third branch flow path 164c is the gap between the first seal mechanism 4 and the first outer seal portion 7. The fourth branch flow path 164d and the fifth branch flow path 164e each branch off from the first main flow path 161a. The fourth branch flow path 164d mainly supplies the cryogenic fluid L to the upper radial bearing 41a. The fifth branch flow path 164e mainly supplies the cryogenic fluid L to the thrust bearing 43. A portion of the cryogenic fluid L that has passed through the thrust bearing 43 is temporarily stored in the upper storage chamber 35. The fourth branch flow path 164d and the fifth branch flow path 164e are, for example, pipes that are arranged at positions radially outwardly away from the outer circumferential surface of the casing 30. Note that the fourth branch flow path 164d and the fifth branch flow path 164e may be provided inside the casing 30.

[0056] (Balance Piping) The balance piping 165 returns the cryogenic fluid L that has passed through the upper radial bearing 41a, the electric motor 50, and the thrust bearing 43 to the intermediate-pressure impeller 55 (in this embodiment, between the second-stage impeller 55b and the third-stage impeller 55c) among the multiple impellers 55. The balance piping 165 in this embodiment includes a first balance piping 165a, a second balance piping 165b, and a third balance piping 165c. The first balance piping 165a returns the cryogenic fluid L that has leaked from the electric motor 50 and the upper radial bearing 41a to a region between the second-stage impeller 55b and the third-stage impeller 55c in the casing 30. The first balance piping 165a mainly returns the cryogenic fluid L that has passed through the electric motor 50 to the intermediate-pressure impeller. The second balance pipe 165b returns the cryogenic fluid L that has leaked from the upper radial bearing 41a and the thrust bearing 43 to a region between the second-stage impeller 55b and the third-stage impeller 55c in the casing 30. The second balance pipe 165b returns mainly the cryogenic fluid L that has passed through the upper radial bearing 41a to the intermediate-pressure impeller. The third balance pipe 165c returns the cryogenic fluid L that has leaked from the upper accommodating chamber 35 to a region between the second-stage impeller 55b and the third-stage impeller 55c in the casing 30. The third balance pipe 165c returns mainly the cryogenic fluid L that has passed through the thrust bearing 43 to the intermediate-pressure impeller 55. The first balance pipe 165a, the second balance pipe 165b, and the third balance pipe 165c are pipes that are arranged radially outward from the outer circumferential surface of the casing 30, for example. The first balance pipe 165a, the second balance pipe 165b, and the third balance pipe 165c may be provided inside the casing 30. Furthermore, the pressure difference between the spaces inside the casing 30 connected by the balance pipes 165 is reduced, and the thrust force acting on the first seal mechanism 4 in the direction of the axis O is suppressed.

[0057] (Flow of Cryogenic Fluid) Next, a description will be given of the flow of the cryogenic fluid when the pump device 1 is in operation. As shown in Fig. 2, when the electric motor 50 is driven, the rotary shaft 21 is driven to rotate, and the impeller 55 and inducer 6 fixed to the rotary shaft 21 rotate. At this time, the radial bearing 41 bears a load on the rotary shaft 21 in a direction perpendicular to the rotary shaft 21 (radial direction). Furthermore, the thrust bearing 43 bears a load on the rotary shaft 21 in the direction of the axis O.

[0058] The cryogenic fluid L in the liquid storage chamber 15 is drawn into the suction section 34 by the inducer 6 and is pressurized in stages by the multiple impellers 55. The cryogenic fluid L drawn into the suction section 34 by the inducer 6 is pressurized by the first-stage impeller 55a. The cryogenic fluid L then passes through the first main flow path 161a and is sent to the second-stage impeller 55b. The cryogenic fluid L is further pressurized by the second-stage impeller 55b and the third-stage impeller 55c to become an intermediate-pressure cryogenic fluid L. Most of the intermediate-pressure cryogenic fluid L passes through the second main flow path 161b and is sent to the fourth-stage impeller 55d. At this time, a portion of the cryogenic fluid L passes through the first branch flow path 164a and is sent from the third-stage impeller 55c to the lower radial bearing 41b. This cryogenic fluid L has a cooling function as a lubricating liquid for the lower radial bearing 41b.

[0059] The cryogenic fluid L sent from the third-stage impeller 55c to the fourth-stage impeller 55d is further pressurized by the fourth-stage impeller 55d and the fifth-stage impeller 55e to become high-pressure cryogenic fluid L. Most of the high-pressure cryogenic fluid L is sent to the discharge portion 162 through the third main flow path 161c and discharged to the outside of the pump device 101 through the discharge pipe 163. At this time, a portion of the cryogenic fluid L supplied from the fifth-stage impeller 55e to the discharge portion 162 is returned from the fifth-stage impeller 55e to the third-stage impeller 55c through the second branch flow path 164b. In addition, a portion of the cryogenic fluid L supplied to the fourth-stage impeller 55d is supplied to the first seal mechanism 4 and the electric motor 50 above through the third branch flow path 164c. Furthermore, a portion of the cryogenic fluid L flowing through the main flow path 161 is supplied to the upper radial bearing 41a through the fourth branch flow path 164d, and to the thrust bearing 43 through the fifth branch flow path 164e. As a result, the cryogenic fluid L has a cooling function as a lubricant for the first seal mechanism 4, the electric motor 50, the upper radial bearing 41a, and the thrust bearing 43. The cryogenic fluid L supplied to the first seal mechanism 4, the electric motor 50, the upper radial bearing 41a, and the thrust bearing 43 is returned to the intermediate-pressure impeller 55 (between the second-stage impeller 55b and the third-stage impeller 55c) through one of the first balance pipe 165a, the second balance pipe 165b, and the third balance pipe 165c. The cryogenic fluid L returned to the intermediate-pressure impeller 55 is again pressurized in stages by the intermediate-pressure impeller 55 and the high-pressure impeller 55.

[0060] (Operations and Effects) The pump device 101 of the second embodiment has the same configuration as the pump device 1 of the first embodiment, and can achieve the same operations and effects.

[0061] In the present embodiment, the branch flow passage 164 has a third branch flow passage 164c that mainly supplies the cryogenic fluid L to the electric motor 50, a fourth branch flow passage 164d that mainly supplies the cryogenic fluid L to the upper radial bearing 41a, and a fifth branch flow passage 164e that mainly supplies the cryogenic fluid L to the thrust bearing 43. Furthermore, the balance piping 165 has a first balance piping 165a that mainly returns the cryogenic fluid L that has passed through the electric motor 50 to the intermediate-pressure impeller, a second balance piping 165b that mainly returns the cryogenic fluid L that has passed through the upper radial bearing 41a to the intermediate-pressure impeller, and a third balance piping 165c that mainly returns the cryogenic fluid L that has passed through the thrust bearing 43 to the intermediate-pressure impeller 55.

[0062] As a result, the pump device 101 can supply the cryogenic fluid L to each of the electric motor 50, the upper radial bearing 41a, and the thrust bearing 43, and return the cryogenic fluid L from each of the electric motor 50, the upper radial bearing 41a, and the thrust bearing 43 to the intermediate-pressure impeller 55. Therefore, differences in the amount of cryogenic fluid L supplied and the temperature at the time of supply between the electric motor 50, the upper radial bearing 41a, and the thrust bearing 43 are suppressed.

[0063] (Other Embodiments) Although the embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like within the scope that does not deviate from the gist of the present disclosure are also included.

[0064] <Additional Notes> The pump devices 1 and 101 described in the respective embodiments can be understood, for example, as follows.

[0065] (1) The pump device 1, 101 according to the first aspect includes a rotating shaft 21 having an axis O extending in the vertical direction as its center, an upper radial bearing 41a supporting an upper portion of the rotating shaft 21 so as to be rotatable about the axis O, a lower radial bearing 41b supporting a lower portion of the rotating shaft 21 so as to be rotatable about the axis O, a first seal mechanism 4 provided between the upper radial bearing 41a and the lower radial bearing 41b and through which the rotating shaft 21 is inserted, and a seal mechanism 4 for rotating the rotating shaft 21 about the axis O between the upper radial bearing 41a and the first seal mechanism 4. The compressor comprises an electric motor 50, a plurality of impellers 55 that are provided below the first sealing mechanism 4 and that pressurize a low-viscosity low-temperature fluid L from below to above as the rotating shaft 21 rotates around the axis O, and a second sealing mechanism 5 that is provided between the lower radial bearing 41b and the first sealing mechanism 4 and through which the rotating shaft 21 is inserted, the plurality of impellers 55 including a pair of the impellers 55 mounted back to back, and the second sealing mechanism 5 is provided at the mounting position of the pair of the impellers 55 mounted back to back.

[0066] According to the above-described configuration, both the upper and lower ends of the rotating shaft 21 are supported by the upper radial bearing 41a and the lower radial bearing 41b. This suppresses vibration of the rotating shaft 21 as a whole. The electric motor 50 and impeller 55, which are vibration sources, are disposed between the upper radial bearing 41a and the lower radial bearing 41b, and the first seal mechanism 4 is disposed between the electric motor 50 and the impeller 55. The first seal mechanism 4 is, for example, a so-called balance sleeve. Furthermore, a second seal mechanism 5 is provided at the mounting position of the pair of impellers 55 mounted back-to-back. The second seal mechanism 5 is, for example, a so-called center stage. The first seal mechanism 4 and the second seal mechanism 5 damp the rotating shaft 21, further suppressing vibration of the rotating shaft 21. Therefore, the cryogenic fluid pump 20 of this embodiment can suppress vibration even when pumping high-pressure, large-flow fluid.

[0067] (2) The pump device 1, 101 of the second aspect is the pump device 1, 101 of (1), and the lower radial bearing 41b may be provided between two adjacent impellers 55.

[0068] The pump device 1, 101 can supply the low-temperature fluid L, which is pressure-fed by the impeller 55, to the lower radial bearing 41b. This allows the pump device 1, 101 to lubricate the lower radial bearing 41b while cooling the lower radial bearing 41b.

[0069] (3) The pump device 1, 101 of the third aspect may be the pump device 1, 101 of (1) or (2), and may be provided with an inducer 6 that is arranged below the lower radial bearing 41b and the plurality of impellers 55 and that draws in the low-temperature fluid L.

[0070] As a result, the suction of the low-temperature fluid L is not hindered by the lower radial bearing 41 b or the impeller 55 .

[0071] (4) The pump device 1, 101 of the fourth aspect may be any one of the pump devices 1, 101 of (1) to (3), and may pump the low-temperature fluid L at a pressure of 0.5 to 3.0 MPa and a flow rate of 1.5 to 10.0 t / h.

[0072] When pumping the cryogenic fluid at a pressure of 0.5 to 3.0 MPa and a flow rate of 1.5 to 10.0 t / h, the pump devices 1, 101 can suitably suppress vibrations while pumping the cryogenic fluid at a high pressure and a large flow rate.

[0073] (5) A fifth aspect of the pump device 1, 101 is a pump device 1, 101 according to any one of (1) to (4), and includes a thrust bearing 43 arranged above the upper radial bearing 41a, and a cryogenic fluid flow path 60, 160 for circulating the cryogenic fluid L. The cryogenic fluid flow path 60, 160 may include a main flow path 61, 161 for circulating the cryogenic fluid L so that it passes through the plurality of impellers 55, a branch flow path 64, 164 branching from the main flow path 61, 161 and circulating the cryogenic fluid L so that it passes through the upper radial bearing 41a, the lower radial bearing 41b, the electric motor 50, and the thrust bearing 43, and a balance pipe 65, 165 for returning the cryogenic fluid L that has passed through the upper radial bearing 41a, the electric motor 50, and the thrust bearing 43 to the impeller 55 with an intermediate pressure among the plurality of impellers 55.

[0074] As a result, the flow of the cryogenic fluid L is branched from the impeller 55 and supplied to the upper radial bearing 41 a, the lower radial bearing 41 b, and the electric motor 50. The cryogenic fluid pump 20 can cool and lubricate the upper radial bearing 41 a, the lower radial bearing 41 b, and the electric motor 50 using this branched cryogenic fluid L. Furthermore, according to this aspect, the cryogenic fluid pump 20 can return the cryogenic fluid L that has passed through the electric motor 50 and the upper radial bearing 41 a to the intermediate-pressure impeller 55 via the balance piping 65, 165, and circulate it. Furthermore, because the cryogenic fluid L is returned to the intermediate-pressure impeller 55, gasification of the cryogenic fluid L is suppressed.

[0075] (6) The pump device 1, 101 of a sixth aspect is the pump device 1, 101 of any one of (1) to (5), and the cryogenic fluid L may be liquid hydrogen.

[0076] When the cryogenic fluid L is liquid hydrogen, the pump devices 1 and 101 can effectively suppress vibration while pumping the cryogenic fluid L at a high pressure and a large flow rate.

[0077] According to the pump device of the present disclosure, vibrations can be suppressed even when pumping a low-viscosity cryogenic fluid at high pressure and large flow rate.

[0078] REFERENCE SIGNS LIST 1 Pump device 2 Supply pipe 3 Gas discharge pipe 4 First seal mechanism 5 Second seal mechanism 6 Inducer 7 First outer seal portion 8 Second outer seal portion 10 Sump 11 Sump body 12 Outer flange 13 Upper flange 14 Mounting wall portion 15 Liquid storage chamber 20 Cryogenic fluid pump 21 Rotating shaft 30 Casing 31 Motor casing 32 Pump casing 33 Flange portion 33a Upper flange 33b Lower flange 34 Suction portion 35 Upper storage chamber 40 Bearing device 41 Radial bearing 41a Upper radial bearing 41b Lower radial bearing 42 Thrust disk 43 Thrust bearing 50 Electric motor 51 Stator 52 Rotor 55 Impeller 55a First stage impeller 55b Second stage impeller 55c Third stage impeller 55d Fourth stage impeller 55e Fifth stage impeller 60 Cryogenic fluid flow path 61 Main flow path 61a First main flow path 61b Second main flow path 61c Third main flow path 62 Discharge section 63 Discharge pipe 64 Branch flow path 64a First branch flow path 64b Second branch flow path 64c Third branch flow path 65 Balance piping 101 Pump device 160 Cryogenic fluid flow path 161 Main flow path 161a First main flow path 161b Second main flow path 161c Third main flow path 162 Discharge section 163 Discharge pipe 164 Branch flow path 164a First branch flow path 164b Second branch flow path 164c Third branch flow path 164d Fourth branch flow path 164e Fifth branch flow path 165 Balance piping 165a First balance piping 165b Second balance pipe 165c Third balance pipe Dv Up-down direction Dvu Upper side Dvd Lower side L Low temperature fluid O Axis

Claims

1. A pump device comprising: a rotating shaft centered on an axis extending in the vertical direction; an upper radial bearing supporting an upper part of the rotating shaft rotatably about the axis; a lower radial bearing supporting a lower part of the rotating shaft rotatably about the axis; a first seal mechanism provided between the upper radial bearing and the lower radial bearing, and through which the rotating shaft is inserted; an electric motor that drives the rotating shaft to rotate about the axis between the upper radial bearing and the first seal mechanism; a plurality of impellers provided below the first seal mechanism and that pressurize a low-viscosity cryogenic fluid from below to above as the rotating shaft rotates about the axis; and a second seal mechanism provided between the lower radial bearing and the first seal mechanism, and through which the rotating shaft is inserted, wherein the plurality of impellers include a pair of impellers mounted back to back, and the second seal mechanism is provided at an attachment position of the pair of impellers mounted back to back.

2. The pump device according to claim 1, wherein the lower radial bearing is provided between two adjacent impellers.

3. A pump device according to claim 1 or 2, further comprising an inducer that is provided below the lower radial bearing and the plurality of impellers and that draws in the cryogenic fluid.

4. The pump device according to claim 1 or 2, wherein the cryogenic fluid is pumped at a pressure of 0.5 to 3.0 MPa and a flow rate of 1.5 to 10.0 t / h.

5. A pump device according to claim 1 or 2, comprising: a thrust bearing arranged above the upper radial bearing; and a cryogenic fluid flow path for circulating the cryogenic fluid, wherein the cryogenic fluid flow path comprises: a main flow path for circulating the cryogenic fluid so as to pass through the plurality of impellers; branch flow paths branching from the main flow path for circulating the cryogenic fluid so as to pass through the upper radial bearing, the lower radial bearing, the electric motor, and the thrust bearing; and balance piping for returning the cryogenic fluid that has passed through the upper radial bearing, the electric motor, and the thrust bearing to the impeller of the plurality of impellers at an intermediate pressure.

6. A pump device according to claim 1 or 2, wherein the cryogenic fluid is liquid hydrogen.

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