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Fluid conveying machineRelated Patent Categories: Pumps, Motor Driven, Pump Rotor Intermediate Coaxial Motor RotorsFluid conveying machine description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070110595, Fluid conveying machine. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a fluid conveying machine, and more particularly to a fluid conveying machine such as a pump suitable for high-speed operation. BACKGROUND ART [0002] In a general motor, a magnetic flux distribution in a clearance between a stator and a rotor is of a rotational symmetry. In principle, no magnetic levitation force is produced in a radial direction. In contrast to the general motor, a magnetic levitation motor eccentrically locates a magnetic flux distribution in which two rotating magnetic fields are superposed between a rotor and a stator to produce a radial force. Specifically, there has been known a magnetic levitation motor which forms two rotating magnetic fields, the numbers of poles of which are different from each other by two, in the stator so as to provide a static magnetic force to the rotor in the radial direction and provide a rotational driving force to the rotor by superposition of the two rotating magnetic fields having different poles. [0003] The magnetic levitation motor has both functions as a radial magnetic bearing and a motor. Thus, the magnetic levitation motor has functions to produce a rotational driving force on a rotor and to support the rotor in a non-contact manner in a radial direction by a magnetic levitation force. The function to support the rotational shaft in a non-contact manner in the radial direction can provide support for the rotational shaft in a non-contact manner even under an environment in which general bearings cannot be used, e.g., under an ultra-low temperature vacuum environment. Further, since the rotational shaft is supported in a non-contact manner, there are not friction nor wear. For example, the magnetic levitation motor is suitable for a conveying machine for a fluid which extremely needs to avoid mixing impurities, for example, ultrapure water. [0004] Further, in a general centrifugal pump, a fluid force is produced in a suction direction (axial direction) at the time of operation to increase a load on an axial bearing. Accordingly, when an output of the pump is increased by operation such as increasing its rotational speed, an axial force applied to the rotational shaft is increased. In order to support the increased axial force, the axial magnetic bearing should be increased in size, thereby lengthening its axial dimension. [0005] Further, when an impeller or an axial magnetic bearing is attached to an end of the rotational shaft, a bending frequency of the rotational shaft is lowered as compared to a case where an impeller or an axial magnetic bearing is attached to the center of the rotational shaft. Accordingly, the limit of rotational speeds, which is determined by a bending frequency, is problematically lowered. Furthermore, since the amount of eccentricity due to bending of the rotational shaft is increased, weight unbalance of the rotational shaft is increased to produce a large vibration at the time of high-speed rotation. [0006] Further, the output of the centrifugal pump is increased as its rotational speed is increased. Accordingly, the same output can be obtained by a small-sized impeller when the pump is operated with high-speed rotation. This miniaturization reduces the weight of the rotating body, increases the resonance frequencies of the axis, and facilitates magnetic levitation control. However, the high-speed operation of the pump induces cavitation to cause breakage of the impeller. Accordingly, increase of the rotational speed has a limitation. DISCLOSURE OF INVENTION [0007] The present invention has been made in view of the above drawbacks. It is, therefore, an object of the present invention to provide a fluid conveying machine having a small-sized compact structure capable of high-speed operation. [0008] According to an aspect of the present invention, there is provided a fluid conveying machine having a small-sized compact structure capable of high-speed operation. The fluid conveying machine has a rotational shaft, a double suction type pump, and at least one magnetic levitation motor having a function as a radial magnetic bearing for supporting the rotational shaft in a non-contact manner and a function as a motor for rotating the rotational shaft. The double suction type pump has a double suction type impeller attached to the rotational shaft, a pump casing disposed so as to surround the impeller, and a pressure balance mechanism for positioning the rotational shaft in an axial direction. [0009] According to the present invention, the rotational shaft is supported in a non-contact manner in a radial direction by the magnetic levitation motor and is positioned in a thrust direction by the pressure balance mechanism of the double suction type pump. Therefore, an axial bearing and an axial disk of the rotational shaft can be eliminated. Accordingly, it is possible to reduce the axial length of the rotational shaft. Further, since the rotational shaft is supported in a non-contact manner by the magnetic levitation motor, there is no friction or wear. Furthermore, the limit of rotational speeds, which is determined by a bending frequency, is increased by the shortened rotational shaft. Thus, a structure suitable for high-speed operation can be obtained. By providing the pump having the double suction type impeller, a rotational speed at which cavitation begins to be generated can be increased. Accordingly, even if the pump is operated at a high speed, cavitation is unlikely to be generated. Thus, stable high-speed operation of the pump can be achieved. Further, by increasing the rotational speed, a small-sized pump having a high output can be obtained. [0010] It is desirable that the pump is disposed substantially at the center of the rotational shaft in the axial direction, and that two magnetic levitation motors are disposed on both sides of the pump. Since a frequency of an axis eigenvalue is increased, levitation stability region is enlarged to higher frequencies. This contributes to improvement of levitation stability. [0011] The pump casing may have a double volute. In this case, radial components of a fluid force applied to the rotating body can be reduced so as to reduce energy loss. The pump casing may have a diffuser. In this case, radial components of a fluid force applied to the rotating body can be reduced so as to reduce energy loss. [0012] Further, it is desirable that the pressure balance mechanism has a pair of variable clearances between each side of the impeller and the pump casing to balance pressures on both sides of the impeller by sizes of the pair of variable clearances. The rotational shaft having the pump impeller can readily and reliably be positioned in the axial direction without using any axial disk or axial bearing. [0013] As described above, according to the present invention, there can be provided a fluid conveying machine such as a pump which can reduce its axis length, minimize an influence of cavitation, operate at high speeds, and have a small-sized compact structure and a high output. BRIEF DESCRIPTION OF DRAWINGS [0014] FIG. 1 is a cross-sectional front view of a fluid conveying machine according to an embodiment of the present invention; [0015] FIG. 2 is a cross-sectional view showing an example of a volute portion in the fluid conveying machine shown in FIG. 1; [0016] FIG. 3 is a cross-sectional front view showing an example of an interior of a pump in the fluid conveying machine shown in FIG. 1; and [0017] FIG. 4 is a cross-sectional view showing another example of a volute portion in the fluid conveying machine shown in FIG. 1. BEST MODE FOR CARRYING OUT THE INVENTION [0018] A fluid conveying machine according to embodiments of the present invention will be described below with reference to FIGS. 1 through 4. In FIGS. 1 through 4, parts or elements having the same function are denoted by the same reference numerals, and will not be described repetitively. [0019] FIG. 1 shows a double suction type pump (fluid conveying machine) according to an embodiment of the present invention. The fluid conveying machine has a double suction type pump 16 disposed at a central portion thereof A rotational shaft 11 of the pump 16 is rotated by magnetic levitation motors 12 and 13 disposed on both sides of the pump 16 and supported in a non-contact manner by the magnetic levitation motors 12 and 13, which serve as radial magnetic bearings. Displacement sensors 19 are disposed on both sides of the magnetic levitation motors 12 and 13. The magnetic levitation motors are controlled by a controller (not shown) based on measured displacements of the rotational shaft 11 so as to support the rotational shaft 11 in a levitated state at a predetermined position. Further, touchdown bearings 20 are disposed on both sides of the displacement sensors 19. Continue reading about Fluid conveying machine... Full patent description for Fluid conveying machine Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Fluid conveying machine patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Fluid conveying machine or other areas of interest. ### Previous Patent Application: Pump apparatus, systems and methods Next Patent Application: Methods and apparatus for transporting natural gas through a pipeline Industry Class: Pumps ### FreshPatents.com Support Thank you for viewing the Fluid conveying machine patent info. 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