Patent Publication Number: US-6213736-B1

Title: Electric motor pump with magnetic coupling and thrust balancing means

Description:
FIELD OF INVENTION 
     This invention relates to an electric motor pump for corrosive, electric conductive, cryogenic and/or hazardous liquids which is submerged in the liquid. 
     BACKGROUND OF INVENTION 
     Submerged electric motor pumps for corrosive, electric conductive, cryogenic and/or hazardous liquids have a high rate of failure, because small leaks and cracks between the electric windings of the stator and the liquid cause chemical or physical disintegration of the electric motor. The bearings of the centrifugal pump have a high rate of failure, due to the above listed agressive liquids and the high centrifugal pump thrust. 
     The objective of the invention is to generate a submerged electric motor pump with the ability to operate in corrosive, electric conductive, cryogenic and/or hazardous liquids with a low rate of failure. 
     SUMMARY OF THE INVENTION 
     The proposed inventive solution suggests a centrifugal pump in a pump housing and an electric motor in a separate motor housing, and the power is transmitted through a magnetic coupling, whereby a thrust equalizing device is mounted on the rotating pump shaft. 
     The motor housing is connected to a tubular device and the power cable is inside the tubular device and on one end connected to the electric motor stator and on the other end to the electric power grid. 
     The motor housing and the tubular device contain an inert fluid like nitrogen or helium gas under higher pressure than the surrounding liquid. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURE 
     The present invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawing, wherein like reference numerals refer to like parts, in which: 
     FIG. 1 is a cross section of the electric motor pump with magnetic coupling and thrust balancing means. 
    
    
     In a further preferred embodiment the electric motor pump is operating as a reverse running pump in the turbine mode and the electric motor is an induction motor operating as an induction generator rotating with over synchronous rotational speed thus generating electric power. 
     The thrust equalizing device  15  increases the life time of the bearings  2  of the rotating pump shaft  1 . 
     The magnetic coupling with two matching rotating parts  10  and  11 , separated through the non-rotating cup  12 , transmits the shaft power between the motor or the generator and the pump or the reverse running pump in turbine mode and separates mechanically the pump from the motor in such a way that the pumped liquid cannot penetrate into the motor housing  7 . 
     The inert fluid  16  under higher pressure than the surrounding pumped liquid prevents the penetration of the pumped liquid into the motor housing in the case of leaks and cracks and prevents the chemical or physical disintegration of the electric motor. 
     The inventive solution is to provide an electric motor pump driven by a magnetic coupling with a thrust equalizing device and an inert fluid inside the motor housing under higher pressure than the surrounding pumped liquid. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 which shows the cross section of the electric motor pump, whereby the rotating pump shaft  1  mounted in two bearings  2  in the pump housing  3  is mounted with one or more centrifugal pump impellers  4  and with one rotating part  10  of the magnetic coupling. The non rotating cup  12  of the magnetic coupling is mounted to the motor housing  7 . 
     The rotating motor shaft  5  mounted in two bearings  6  in the motor housing  7  is mounted with the electric motor rotor  8  and with one rotating part  11  of the magnetic coupling matching the rotating part  10 , and separated from each other through the non rotating cup  12 . 
     The tubular device  13  is flexible for the preferred embodiment and mounted to the motor housing  7 . The power cable  14  is inside the tubular device  13  and on one end connected to the electric motor stator  9  and on the other end to the electric power grid. 
     A thrust equalizing device  15  as it is prior art for centrifugal pumps and described in several publications is mounted on the rotating pump shaft  1 . 
     The motor housing  7  and the tubular device  13  contain an inert fluid  16 , which is for the preferred embodiment nitrogen, helium or argon gas, under higher pressure than the surrounding pumped liquid.