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Pump with electric motor, immersed in the fluid to be pumpedPump with electric motor, immersed in the fluid to be pumped description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080080988, Pump with electric motor, immersed in the fluid to be pumped. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]1. Field of the Invention [0002]The invention relates to a pump with electric motor, completely immersed, including the motor, in the fluid to be pumped. A pump of this type is, for example, used for pumping a cold liquid such as liquefied natural gas wherein said liquid is used as a fluid for cooling specific elements of the pump, in particular the electric motor, and also for the dynamic axial balancing of the rotational parts. The invention relates, more specifically, to a new arrangement of circuits for the auxiliary circulation of fluid allowing these operations to be carried out. [0003]2. Description of the Related Art [0004]A type of pump is known in which the suction stage, located in the lower portion of a casing, is surmounted by an electric drive motor accommodated in the same casing. Said casing is designed to be plunged into the fluid to be pumped. For example, a pump of this type can be used for the pumping of liquefied natural gas contained in a tank. The pump is immersed into the liquefied gas, preferably generally vertically down to the bottom of the tank. A pump of this type is, for example, described in U.S. Pat. No. 3,652,186. The common shaft of the electric motor and the suction stage is supported by rolling bearings. [0005]The suction stage is followed by a centrifugal wheel connected to the shaft and the structure of said wheel is utilised in order to form an axial balancing system defined by a circuit for fluid circulation, of the actual fluid to be pumped, provided between the centrifugal wheel and the casing. During operation, this balancing system relieves the mechanical rolling bearings. A small portion of the pumped fluid is therefore removed in order to feed this balancing system. [0006]It is also known to remove pumped fluid in order to cool specific elements of the pump, in particular the electric motor and at least one mechanical rolling bearing, especially the main rolling bearing, located in proximity to the fluid balancing system. [0007]Although the pump is able to operate in any position, it is particularly designed to be positioned vertically, with the suction stage at the bottom. This is why, for the remainder of the description, the terms "lower" or "upper" will be used, for example, in order to define the position of one element in relation to another. SUMMARY OF THE INVENTION [0008]The invention proposes to optimise the internal auxiliary circulations of fluid in the pump in order to improve the performance levels of the balancing system and those of the cooling stream. [0009]The invention therefore relates primarily to an electric motor pump immersed in the fluid to be pumped, comprising a casing intended to be plunged into said fluid and accommodating, on the one hand, at least one centrifugal wheel and, on the other hand, a coaxial electric motor surmounting said centrifugal wheel and comprising a stator which is integral with said casing and a rotor which is integral with a shaft coupled to said centrifugal wheel, a first rolling bearing mounted between said shaft and said casing being installed between said centrifugal wheel and said motor, and an axial balancing system being defined by a fluid circulation circuit provided between said centrifugal wheel and said casing, characterised in that it also comprises at least one fluid cooling circuit, in particular for said motor and/or said first rolling bearing, and in that said supply circuit of said axial balancing system is independent of the or of each cooling circuit. [0010]Under these conditions, there is maximum pressure available for each operation (dynamic balancing and cooling) and minimum temperature. These two conditions combined have been found to be important for effective operation of the axial balancing system and the cooling circuits. The invention also allows elimination of the risks of internal vaporisation (cavitation) of the fluid circulating in the auxiliary circuits defined hereinbefore. [0011]Moreover, the various fluid circulation auxiliary circuits are easy to install in the pump. [0012]Advantageously, the fluid cooling circuit of the electric motor passes through the air gap thereof. [0013]According to one embodiment, the motor is installed in an inner jacket of the casing, defining in said jacket a lower chamber (between said first rolling bearing and the motor) and an upper chamber above the motor. The cooling circuit of the motor comprises inlet orifices formed in the wall of the inner jacket and establishing communication between an evacuation conduit downstream of said centrifugal wheel and the lower chamber. At least one discharge conduit communicating with the upper chamber is provided in order to reintroduce the fluid used for the cooling into the reservoir in which it is stored. [0014]The axial balancing system comprises a high-pressure flow space defined between the casing and a lower (front) face of said centrifugal wheel and a low-pressure flow space defined between the casing and an upper (rear) face of this same centrifugal wheel, said low-pressure flow space being limited radially internally by an annular passage forming an axially variable flow restriction. Reinjection channels are provided in said centrifugal wheel between an annular discharge space and the inlet of the centrifugal wheel (where the fluid is at a lower pressure). The annular discharge space is defined around the shaft, radially internally in relation to said annular passage forming the variable flow restriction. BRIEF DESCRIPTION OF THE DRAWINGS [0015]The invention will be better understood and further advantages thereof will become clearer in the light of the following description of a pump in accordance with the principle of the invention, given solely by way of example and with reference to the appended drawing, in which: [0016]the single FIGURE shows a cross-section and elevation of the pump in accordance with the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0017]The illustrated pump comprises a, generally cylindrical, casing 12 accommodating a suction stage 14 and an electric motor 16. Said motor comprises a stator 18 which is integral with the casing and a rotor 20 equipped with a drive shaft 22, the axis of which coincides with that of the suction stage. The shaft 22 is mechanically coupled to the suction stage 14 which comprises mainly an Archimedes' screw drive unit, referred to hereinafter as the impeller 26. The suction stage is surmounted by a centrifugal wheel 28 which is known per se. A diffuser 30, the fixed blades 31 of which are integral with the casing, is installed coaxially between the impeller 26 and the centrifugal wheel 28. Under normal operating conditions, the pump is designed to be positioned at least approximately vertically and immersed into the fluid to be pumped, with the end 34 of the casing that is closest to the impeller being positioned in the bottom portion. The pumping inlet 35 is defined in the vicinity of this lower end 34. Under these conditions, i.e. viewing the pump set up vertically, there is successively found in the casing, from bottom to top, the impeller 26, the diffuser 30, the centrifugal wheel 28 and the electric motor 16 driving the shaft 22. This shaft and also the rotating parts of the pump which are integral therewith are supported by two rolling ball bearings which are coaxial and set apart on either side of the motor: a first, main, rolling bearing 38 located between the suction stage 14 and the motor 16, more precisely just above the centrifugal wheel 28, and a second rolling bearing 40 located above the motor. For each rolling bearing, the inner cage is fixed to the shaft whereas the outer cage is mounted so as to slide in a bore in the casing 12 in such a way that all of the rotating elements of the pump are able to move in the longitudinal direction of the shaft. [0018]Said first rolling bearing 38 is installed at the centre of a transverse wall 44 of the casing that separates the suction stage from the motor. The stator of the electric motor is integral with an inner jacket 46 of the casing, which jacket is coaxial with the shaft, in such a way that the air gap 48 of the motor, defined between the exterior of the rotor and the interior of the stator, establishes communication between a lower chamber 50 of said inner jacket (extending between said first rolling bearing and the lower end of the motor) and an upper chamber 52 of said inner jacket, extending between the motor and said second rolling bearing. During operation, said inner jacket is filled with the fluid to be pumped. [0019]An annular conduit 54 communicating with the outlet 56 of the centrifugal wheel 28 extends around said inner jacket 46 and opens, at its lower portion, into a conduit 58 for evacuating the pumped fluid. [0020]A dynamic balancing system 60 defined by a double circuit for the circulation of pumped fluid is provided between the centrifugal wheel and the casing. This balancing system comprises a high-pressure flow space 62 defined between the casing and a lower face of the centrifugal wheel and a low-pressure flow space 64 defined between the casing (more specifically, said transverse wall 44 in which said first rolling bearing is mounted) and an upper face of the centrifugal wheel. Continue reading about Pump with electric motor, immersed in the fluid to be pumped... Full patent description for Pump with electric motor, immersed in the fluid to be pumped Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Pump with electric motor, immersed in the fluid to be pumped 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. 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