Abstract:
The present invention discloses structural improvement of the vertical submerged pump for chemical application. The present invention is focus on reducing the crystal lump generated from high speed etching process. Structural improvement includes a shaft seal device, a diffuser and an upper inner plate. The shaft seal device offer extra flow resistance to balance the differential pressure between the inner space and pump front casing, the function are prevents air bubbles be sucked into the pump, and reduces flow leakage from the front casing into inner space, also absorbs high-pressure back-flush to avoid liquid splash in dry surface of inner space of support column. The diffuser in the support column offer extra inducer function to guides the liquid from the inner space flowing out to the tank, so as to get a stable liquid level in the inner space, thereby largely reducing splashing of the liquid. And the upper inner plate blocks the residual small amount drops from liquid splashing, to minimize producing of crystals lump from high speed etching liquid.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    a) Field of the Invention 
         [0002]    The present invention relates to the structural improvement of a vertical submerged pump for chemical application, and more particular in high speed etching process in PCB manufacturing, owing to the drops from splashing of process liquid easily become crystal when attach to dry surface and contact with air, the crystal will damage the shaft seal and lead motor to be broken, so as to reduce liquid splashing from pump shaft to avoid generation of crystals is an important issue. The present invention improve the structure to control the liquid level in an inner space of a support column of a submerged vertical pump, especial when the process liquid is at over upper liquid level, thereby decreasing damage to a shaft seal of a motor, and avoiding the corrosive vapor entering into the motor to cause malfunction. 
         [0003]    b) Description of the Prior Art 
         [0004]    Referring to  FIG. 1 , a conventional vertical submerged pump is used in chemical plating or etching process to transfer strong acid, strong base or corrosive liquid. A practical operation is described as follows. A cantilever shaft  3  be installed inside the support column  1 , and at the lower side of the cantilever shaft  3  is directly connected with the hub  52  of impeller  5 . At rear side of the impeller  5  is provided with back vanes  51  to balance axial thrust. The impeller  5  is provided in a front casing  4  which is opened with an inlet port  44 . A side of the front casing  4  is opened with an outlet port  45  which is connected to a discharge pipe  43 . In a real condition, liquid sucked flow in the inlet port  44  by the impeller  5  along the direction  28 , is pressurized flowing through a flow channel of the impeller  5  and is then discharged from the outlet port  45 . 
         [0005]    When the pump operates, the shaft sleeve  31  of the cantilever shaft  3  has a tangential velocity U (as shown in  FIG. 2 ) at outer surface, will drive the liquid in the inner space  12  to flow in free vortex  2  with a distribution of the tangential velocity  267  shown in the drawing. The free vortex  2  is also provided with a stream line of a secondary flow  22  with lower kinetic energy, and at the center of the vortex is formed with a hollow space  21  which is as a funnel extended downward. A flow direction of the free vortex  2  is also provided with the stream line of the secondary flow  22  on an r-z cross section at the same time, and the hollow space  21  is a primary zone where air  24  be sucked and mixed with the liquid to produce bubbles  241 , allowing the back vanes  51  to attract the bubbles  241  to flow downward. For example, the liquid which contains bubbles  242  flows through the clearance of back cover  42  between back cover and the shaft, and then enter into the front casing  4 , bubbles  242  will be pressurized into bubbles  243  in smaller diameters and exported through the discharge pipe  43  from the outlet port  45 . The bubbles also flow through lower holes  11  of the support column  1 , diffuser holes  112  of the support column I and upper holes  111  of the support column  1  into the tank along the direction  23 . 
         [0006]    Referring to  FIG. 2 , after the liquid that is close to a surface of the shaft sleeve  31  of the cantilever shaft  3  receiving kinetic energy of rotation of the pump, a tangential velocity distribution Cu will be close to the tangential velocity U at the outer surface of the shaft sleeve  31  of the cantilever shaft  3 . However, a free surface of free vortex  2  has the energy conservation feature from Bernoulli theorem, the energy conserve with kinetic energy, that is velocity, and potential energy, that is liquid level reference from tank level. The total energy is transferred from the shaft to the liquid and the free surface of the free vortex  2  has the same energy, and the energy will convert to both kinetic energy and potential energy, it depend on the tangential velocity which is low or high, if tangential velocity is low then the potential energy must be high, that means liquid level is high. The tangential velocity distribution Cu of the free vortex  2  decreases as the radius r increases, and is inverse proportional to the radius r (r −1 ); therefore, at the central part of the free vortex  2 , the liquid level will form a funnel which is extended downward due to the fast tangential velocity, that is the maximum flow speed as same as the tangential speed of rotational shaft  3 . On the other hand, as the tangential velocity Cu slow down toward the outer edge  2 A of the free surface, the potential energy will become higher, that allows the liquid level to be higher than both the hollow space  21  and the tank  29 . 
         [0007]    Referring to  FIG. 3 , when the pump discharge capacity become larger, the output pressure will become smaller, and at the same time if the liquid level of the tank  29  is lower, in this condition a low pressure suction force will be generated by the back vanes  51  of the impeller, owing to the force acting on the liquid by the back vanes  51 , and establish a low pressure zone near the impeller hub  52 . The pressure of the low pressure zone maybe is negative pressure in vacuum at some time, when the low pressure is sufficient to overcome the output pressure of the pump, which liquid and air  24  will be sucked and through the clearance  42  at the back cover into the front casing  4 , especially the liquid level at the central part of the free vortex  2  will be low. Although the support column  1  is provided with lower holes  11  to supplement the liquid from the tank, with the liquid flowing in along a direction  26 , the liquid level at the outer edge surface  2 A of the free vortex  2  in the inner space  12  is as low as the liquid level in the tank  29 . If this condition continuously happen, the liquid level of the hollow space  21  will descend significantly or even reach to the back cover  41 , allowing the air bubbles  24  to be sucked into the front casing  4  through the clearance  42  at the back cover, which will cause the pump to operate unstably by sucking in the air bubbles and result in an unstable output of the pump. 
         [0008]    Referring to  FIG. 4 , when the pump discharge capacity is smaller, the output pressure become larger, and the liquid level in the tank  29  is kept high or over level limit, that is a high liquid level manufacture process. At this condition the low pressure suction force of the back vanes  51  is not sufficient to balance the high output pressure, and the high pressure liquid will leak out through the clearance  42  at the back cover  41  along a direction  262  and flow into the inner space  12 . Owing to the leakage, the liquid level will increase in the inner space  12 , the free surface of the free vortex  2  will rise, and especially the outer edge  2 A of free vortex  2  will become higher even over the level limit. Although the support column  1  has some openings with lower holes  11 , diffuser holes  112  and upper holes  111 , but the circumference flow  25  is in tangential flowing, owing to the liquid receiving the rotational kinetic energy transferred from the shaft, so the liquid has strong momentum in circumferential direction and weak in radial direction, the liquid is not easily to flow through the openings  112  out, that is more liquid leakage in and less liquid flow out, the liquid will gradually accumulate in inner space  12  of support column  1 . Therefore, the liquid level at the outer edge surface  2 A of the free vortex  2  will be over the level limit finally, and the liquid could be very close to the undersurface of the motor mounted plate  61 . In addition, some liquid will be splashed on surfaces of a seat of a V-type oil seal  64 , a ceramic seal ring  71  and a V-type oil seal  72 , further producing crystal lumps on these surfaces to damage the V-type oil seal  72 . Moreover, corrosive vapor can enter into the motor to result in malfunction. 
         [0009]    Referring to  FIG. 5 , when the pump shuts down, the impeller  5  will not generate high pressure any more. At this time, the high pressure liquid and compressed air in filtration tanks of the piping system will back flush  271  momentarily from the discharge pipe  43 . This kind high kinetic energy is converted from pressure potential energy of compressed air and high pressure liquid, the back-flush  271  will flow backward out through the inlet port  44  along the direction  281 , and will flush toward the back vanes  51  also. So back-flush  264  with high kinetic energy flow upward through the clearance  42  at the back cover  41  out, and the back-flush  265  will enter into the inner space  12 , in the same time the liquid in the inner space  12  still kept in free vortex motion, such that the lowest level of the hollow space  21  in the vortex center cannot absorbs the kinetic energy of back-flush  265 , and part of the back-flush  266  will spray and splash upward. Especially that during a high liquid level manufacturing process, the back-flush  266  wilt spray onto the dry undersurface  61  of the motor mounted plate, around the shaft hole  62  of the motor mounted plate, the ceramic seal ring  71  and the V-type oil seal  72 . The spraying liquid left to produce crystals when it become dry, this will damage the ceramic seal ring  71  and the V-type oil seal  72 , and further concern the liquid vapor to penetrate into the motor, which will damage motor bearing and the winding. 
         [0010]    Concluding the aforementioned pump operation phenomena, for the application of a high-speed etching process, providing a low-cost solution to stop the crystal lumps formed by liquid splashing will satisfy existing requirements of customers; whereas, issues of problem that the solutions to be faced with are:
       (1) The problem of liquid splashing at the outer edge  2 A of the free vortex  2  in the high liquid level manufacturing process,   (2) The problem of high pressure back flushing in the piping system when the pump be shut down and,   (3) The problem that the air bubbles are sucked into the back vanes of the impeller in the low liquid level manufacturing process.       
 
         [0014]    To completely solve the problems, each problem needs to be analyzed in details. The cause analyses are described as follows:
       (1) The liquid splashing problem: the majority issue is about the liquid level, include the tank liquid level is at high liquid level limit, and also the liquid leaks from front casing into the inner space result in liquid level increasing in inner space till over upper level limit. And another issue is the liquid in free vortex motion in the inner space but the openings on support column are still difficult to let the liquid flowing out to keep the liquid level in stable.   (2) The back flushing problem: It is un-normal operation problem of equipment or piping system by operator, but it always happen because operator&#39;s problem, especially the compressed air accumulated in filtration tanks conditions. Therefore, the pump should be equipped with a device to isolate, guide and absorb the pulse wave of high-pressure back-flush, that let any operator does not worry about this.   (3) The air bubbles sucked-in problem: Sometimes the liquid level in the tank could be low or beyond the low limit. Therefore, the pump should be designed to isolate the low pressure of the back vanes of the impeller and to guide the liquid into the pump casing, so as to prevent larger amount air bubbles from being sucked in to result in an unstable operation.       
 
         [0018]    There are already some solutions to solve the aforementioned problems. One of the solutions is the patent TW221338, which discloses a non-contact labyrinth type seal device of a submerged vertical pump. The patent provides a solution to solve the problems, that the non-contact labyrinth type seal device offer a extra flow resistance to balance the differential pressure between the inner space and the front casing, that is the air bubbles will not be sucked, even a negative pressure produced from the back vanes of the impeller, and the high-pressure liquid flushes back from the piping will be isolated when the pump shuts down. However, this solution is not able to control the liquid at the outer edge of the vortex from splashing, and the leakage become slowly but still leakage from front casing, it will increase the liquid level during the operation till to over liquid level limit, especially liquid tank has a high liquid level conditions, and the last issue of the solution is the reliability of labyrinth type seal device. 
       SUMMARY OF THE INVENTION 
       [0019]    The primary objective of the present invention is to provide a vertical submerged pump for chemical application. Structural improvement includes a shaft seal device, a diffuser and an upper inner plate. The shaft seal device offer extra flow resistance to balance the differential pressure between the inner space and pump front casing. The function are prevents air bubbles be sucked into the pump, and reduces flow leakage from the front casing into inner space, also absorbs high-pressure back-flush to avoid liquid splash in dry surface of inner space of support column, and has reasonable reliability. The diffuser in the support column offer extra inducer function to guides the liquid from the inner space flowing out to the tank, so as to get a stability liquid level in the inner space, thereby largely reducing splashing of the liquid. And the upper inner plate blocks the residual small amount drops from liquid splashing, to minimize producing of crystals lump from high speed etching liquid. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    As indicated in  FIGS. 6 ,  7 ,  8 ,  9 ,  10  and  11 , the present invention is a vertical submerged pump for chemical application. The structural improvement includes a shaft seal device  55 , a diffuser  10  in a support column and an upper inner plate  83  in a support column. The structural improvement comprises of: 
         [0021]    A shaft seal device  55  having a rotor of N-type seal  53  and a stator of N-type seal  54 . The stator  54  is provided at a corresponding position in the rotor  53  after the pump has been assembled, an out surface of the rotor  53  and an inner surface of the stator  54  matching each other to form a non-contact seal channel  56 . The seal channel  56  has two sharp turns with a bending angle of each turn larger than 90°, and has a more than I mm width to improve the reliability. The stator  54  is provided with an outer cylindrical part  543  and a plate part  548  that the stator  54  can be provided on an inner wall of an upper part  46  of the front casing  4  by the plate part  548 . The rotor  53  can be provided on an impeller hub  52  by an inner diameter  536  of the rotor. The stator  54  is provided with two inner surfaces  549  of different radii and a conical part  542  which is extended downward. The rotor  53  is provided with two inner surfaces  532  of different radii and a conical part  531 . The conical part of the stator  542  is provided to fit with the conical part  531  of rotor  53 , and the two form a conical part  561 of the seal channel  56  to extend a seal length of the seal channel  56 , so the seal channel  56  could offer extra flow resistance to balance the differential pressure between the inner space  12  and the front casing  4 . The first sharp turn  564  at the seal channel  56  on the stator  54  is provided with plural radial stator holes  544  which are connected to the inner space  12 , and the second sharp turn  565  at the seal channel  56  on the rotor  53  is provided with radial rotor holes  533  to remove impurities accumulated to release into inner space  12 , the shaft seal device could absorb the kinetic energy of the back-flush high-pressure pulse wave and guide the liquid into inner space then enter the liquid tank. 
         [0022]    A diffuser  10  in the support column guides partially the liquid direction from circumferential direction to radial direction, that is increase the radial velocity component and reduce the tangential velocity. So the liquid will flow out in a small turning angle to increase radial velocity, and some of the kinetic energy be converted into velocity in radial direction to go outward. Accordingly, the structure of the diffuser  10  in the support column  1  could provide a diffusing function and a flow turning function to keep the liquid level in stable at inner space  12 . The diffuser blade  14  has an incident angle a between the inlet flow of the liquid and the inlet of the diffuser blade  14 , such that the liquid will not change the direction significantly at the leading edge  141  of diffuser blade  14 . After the liquid flowing through the cascade the liquid velocity will be slow down and the flow angle will be change by the diffuser blade  14 , this is a diffusion process relative about some of the kinetic energy in circumference will be converted to velocity in radial flowing, and the liquid will flow out through the diffusion holes  15 . So the diffuser  10  can be easily manufactured and installed, as well as cost can be reduced. Three embodiments are listed as follows: 
         [0023]    First embodiment of the diffuser  10  in the pump column  1  is plural blades  14  with span B, which are installed inside the support column I and arranged alternately with plural diffuser holes  112  into circular. In addition, the blades  14  are installed opposite to a direction of the circumferential flow  25 . A leading edge  141  of the diffuser blade  14  faces toward the circumferential flow  25 , and located above the diffuser hole  112 , a trailing edge  142  of the diffuser blade is below the next diffuser hole  112 , and a cross section  145  of the diffuser blade is a smooth arc shape. A flow channel  146  is formed between the diffuser blades  14 , the diffuser hole  112  is located on the wall of the support column  1  in the flow channel  146 , an inlet  147  of the flow channel is constituted by the leading edges  141  of the neighboring diffuser blades, an outlet  148  of the flow channel is constituted by the trailing edges  142  of the neighboring diffuser blades. The free vortex  2  has liquid flow  25  in horizontally circumference direction, an incident angle a is formed between the leading edge  141  of the diffuser blade and the circumference flow  25 , and the liquid enters from the inlet of the flow channel  147  and is guided to flow downward to export from the outlet of the flow channel  148 . When the liquid flows in the flow channel  146 , the diffuser blade  14  will absorb some of the kinetic energy of the liquid to locally increase a static pressure at the flow channel  146 , allowing a bigger pressure difference between the inner wall and the outer wall of the support column  1 . This pressure difference allows the liquid to accelerate out from the diffuser hole  112  and this guiding effect facilitates expelling the excessive liquid in the inner space  12  and keeps the liquid level stable, thereby avoiding the liquid level at the outer edge surface  2 A of the vortex to reach to an upper inner plate  83  of the support column. 
         [0024]    A second embodiment of the diffuser  10  in the support column  1  is with plural diffuser holes  15  only, which are arranged in a circumference of the support column  1  to replace the original diffuser holes  112 . The diffuser holes  15  have an oblique opening and form a small bevel angle β with the circumference flow  25 , so as to induce the liquid to flow out by convert the tangential velocity partially to increase a radial component of the velocity. When the circumference flow  25  driven by the pump shaft  3 , the side wall  153  of the diffuser holes  15  will induce the flow along the wall, and another side wall  154  of the diffuser holes  15  allows the liquid to turn along the diffuser holes  15 , this effect is similar like an water cut or a tongue of a volute pump casing; that is, the radial velocity component of the liquid will increase as flow  26 , and more liquid will flow along the diffuser holes  15  out, and hence, the liquid will be stable by the diffuser holes  15 . 
         [0025]    A third embodiment of the diffuser  10  in the support column  1  is plural longitudinal blades  16  with span B, which are installed in the interior side of the support column  1 , and are arranged alternately with plural longitudinal diffuser holes  17  in circumference. The leading edge  161  of the diffuser blade  16  faces toward the circumference flow  25 , the root  162  of the diffuser blade  16  is located at the side wall  174  of the long diffuser hole  17  and a cross section of the diffuser blade  16  is a smooth arc shape. A flow channel  166  is formed by the diffuser blades  16 , the inner wall of support column  1 , and the longitudinal diffuser hole  17 . The inlet  167  of the flow channel  166  is constituted by the leading edges  161 , the outlet  168  of the flow channel  166  is the longitudinal diffuser hole  17 . The circumference flow  25  with the leading edge of the diffuser blade  161  forms an incident angle γ, the root of the diffuser blade  162  has angle δ with the circumference. The liquid enters from the inlet  167  of the flow channel  166 , and is guided to flow outward from the longitudinal diffuser hole  17 , with smoothly flow angle δ, so as to facilitate the liquid to flow out with the radial velocity component of the velocity as flow  26 . 
         [0026]    An upper inner plate  83  is a ring-shape plate structure, is installed on interior wall of the support column  1  and is closed to a lower rim of the upper hole  111 . The cantilever shaft  3  passes through the center of that ring-shape structure, and keeps a large radial distance with an outer diameter of the shaft sleeve  31 . When the liquid level of the free vortex  2  keeps at a certain height by the diffuser blade  14 , there is still a small amount of the liquid will splash above the support column  1  from the outer edge surface of the vortex  2 A. The upper inner plate  83  can further isolate the splashing liquid, prohibiting the liquid to reach to a undersurface of a motor mounted plate  61 , and keeping surfaces of a seat  64  of V-type oil seal  72 , a ceramic seal ring  71  and a V-type oil seal  72  clean that the V-type oil seal  72  will not be damaged by the crystals, thereby effectively isolating acid vapor to assure that the motor will not be malfunction. 
         [0027]    Referring to  FIG. 7(   a ), it shows a perspective view of a shaft seal device  55 . Referring to  FIGS. 6 and 7(   b ), a shaft seal device  55  has a rotor  53  and a stator  54 , wherein after the pump has been assembled, the rotor  53  is installed at a corresponding position in the inner diameter  549  of the stator  54 . The impeller hub  52  be fixed at the end of the cantilever shaft  3  installed with the shaft sleeve  31 , and pass through the inner diameter  536  of the rotor. The stator  54  uses a structure having a plate part  548  of the stator  54  to facilitate installation and positioning, or only a structure of an outer cylindrical part of the stator  543  is used, referring to  FIG. 7(   c ). The stator  54  can be provided with a screw part  547 , such that the stator  54  can be installed into a screw hole at the upper part of the front casing  46 , or the stator  54  can be installed into an opening at the upper part of the front casing  46  by other methods. 
         [0028]    Referring to  FIG. 8 , it shows a cross-sectional drawing of a shaft seal device  55  be assembled on the vertical submerged pump. Wherein the rotor  53  is a cylindrical structure which is constituted by two cylinders of different radii, the cylindrical part of the rotor  534  and the inner surface of the rotor  532  are linked together by the conical part of the rotor  531  which is extended upward. At bottom of the conical part of the rotor  531  is provided with plural rotor holes  533  to remove impurities which be accumulated in the seal channel  56 , thereby protecting the seal channel  56  from being expanded by wearing out. The stator  54  comprises the plate part  548  and the outer cylindrical part  543 . At interior of the outer cylindrical part  543  is provided with the conical part  542  of the stator  54  which is extended downward, and a top of the conical part  542  is provided with plural radial stator holes  544  which are used to transfer the back-flush pressure wave and are connected to the inner space  12 . After the pump has been assembled, the stator  54  and the rotor  53  will constitute the seal channel  56  which has an inlet  562  and an outlet  563 , the two are of different radii, as well as a conical part  561  of the seal channel  56 . The conical part  561  of the seal channel  56  is located between the inlet  562  and the outlet  563  of the seal channel. When the liquid flows from the inlet of the seal channel  562  toward the conical part  561  of the seal channel  56 , the liquid must flow backward by more than 90° at the first sharp turn  564 , and when the liquid flows from the conical part of the seal channel  561  toward the outlet of the seal channel  563 , the liquid should also flow backward by more than 90° at the second sharp turn  565 , and vice versa when the liquid flows reversely. A highly flow resistance loss will be produced in the seal channel  56  with two sharp turns, even the width of seal channel  56  is more than I mm. The conical part  561  of the seal channel  56  is formed by matching the conical part  531  of the rotor with the conical part  542  of the stator, the inlet  562  and outlet  563  of the seal channel  56  are formed by the inner diameter  549  of the stator  54  and the outer diameter  537  of the rotor  53 , which are of different radii. The first sharp turn  564  of the seal channel  56  corresponds to the plural stator holes  544  which are connected to the inner space  12 , and the second sharp turn  565  of the seal channel  56  corresponds to the plural rotor holes  533  which are connected with the inlet  562  and the outlet  563 . A small amount of the high-pressure liquid in the front casing  4  will flow in from the rotor holes  533 , thereby removing the impurities which are accumulated in the seat channel  56 . 
         [0029]    Referring to  FIG. 9(   a ) when the pump operates in the low liquid level condition, a shaft seal device  55  offers extra flow resistance to balance the differential pressure between the front casing  4  and inner space  12  to avoid the air bubbles sucked into the front casing  4  from inner space  12 . If the back vanes  51  generate negative pressure, the differential pressure will be more serious, then the seal channel  56  with the second sharp turn  565  and the first sharp turn  564  can offer extra flow resistance to avoid the air  24  be sucked into the front casing  4 . The stator holes  544  directly connect to the bottom of the inner space  12 , and the less air bubbles liquid  263  could be sucked in directly, and the stator holes  544  could offer more liquid with less air bubbles flowing in at first sharp turn  564 . So the seal channel  56  could reduce the air bubbles flowing downward 
         [0030]    Referring to  FIG. 9(   b ), when the liquid level  29  is normal, and the pump discharge is high capacity, the shaft seal device  55  could offer extra flow resistance to balance the differential pressure between the inner space  12  and the front casing  4 , to avoid the air bubbles be sucked into the front casing  4 . On the contrary the pump discharge is high pressure, the shaft seal device  55  could offer extra flow resistance to balance the differential pressure between the inner space  12  and the front casing  4 , and to reduce high-pressure liquid leak from the front casing  4  to the inner space  12  through the seal channel  56 . Partly kinetic energy of the high-pressure liquid will loss at the inlet of the seal channel  562 , the conical part  561 , the first sharp turn  564 , and the second sharp turn  565 , then the outlet  563 . Before changing the flow direction at the first turn  564 , some of the liquid will be guided to discharge directly from the stator holes  544  to inner space  12 , the rotation of the conical part  531  of the rotor  53  will increase the flow resistance. At outlet  563 , as the liquid is only provided with very low kinetic energy, the liquid level of the free vortex  2  cannot be fluctuated in inner space  12 . The leakage at flow direction  265  is tow but still causes the liquid level to rise, which will require the diffuser  10  in the pump column  1  to maintain the stability of the liquid level in the inner space  12 . 
         [0031]    Referring to  FIG. 9(   c ), when the pump shuts down, the high-pressure liquid in the piping flushes back momentarily along the back-flush direction  271  from the discharge pipe  43 , flows back to the front casing  4  and exits from the inlet port  44 . Part of the high-pressure back-flush of the liquid  265  will also flush back and flow upward through the back vanes  51  and then the channel seal  56 . Partly kinetic energy of the high-pressure back-flush of the liquid  265  will be loss at the inlet of the seal channel  562 , the conical part  561 , the first sharp turn  564 , and the second sharp turn  565 , then the outlet  563  of the seal channel  562 . At the first sharp turn  564  where the high-pressure back-flush of the liquid  265  will be discharged directly to the inner space  12  along the direction  263 , and two sharp turn will changes the momentum direction significantly. In addition, the kinetic energy of the back-flush liquid  265  will be absorbed by the conical part  561  also. At the end, residual of the back-flush liquid  265  will finally flow out of the outlet of the seal channel  563  and enter into the inner space  12 . As the liquid is only provided with extremely low kinetic energy, the liquid splashing at the level cannot be formed at this time. 
         [0032]    Referring to  FIG. 10(   a ), it shows a schematic drawing of a diffuser blade  14 , which is arranged with the plural diffuser holes  112  of the support column  1 . Referring to  FIG. 10(   b ), it shows a perspective drawing of a diffuser blade  16 , which is arranged with the plural diffuser holes  17  of the support column  1 . 
         [0033]    Referring to  FIG. 11 , it shows a cross-sectional drawing of diffuser holes  15  only, which is arranged in circumference. 
         [0034]    Conclude from the above, in accordance with the present invention, the pump includes the shaft seal device  55 , the diffuser  10  in the pump column and the upper inner plate  83  of the support column. This low-cost and simple structure can effectively isolate the air bubbles from being sucked into the pump, maintain the stable liquid level in the inner space and prevent the liquid from flushing back momentarily to damage the V-type oil seal at the motor side when the pump shuts down. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
       [0035]      FIG. 1  is a cross-sectional drawing of a conventional product. 
         [0036]      FIG. 2  is a drawing of a tangential velocity of free vortex versus a shaft outer radius. 
         [0037]      FIG. 3  is a cutaway drawing of a conventional product, a liquid level of a tank of which is the lowest. 
         [0038]      FIG. 4  is a cutaway drawing of a conventional product, a liquid level of a tank of which is the highest. 
         [0039]      FIG. 5  is a cutaway drawing of a conventional product which shuts down. 
         [0040]      FIG. 6(   a ) is a cross-sectional drawing of an embedment of the present invention. 
         [0041]      FIG. 6(   b ) is cross-sectional drawing of second embedment of the present invention. 
         [0042]      FIG. 6(   c ) is a cross-sectional drawing of third embedment of the present invention. 
         [0043]      FIG. 7(   a ) is a perspective drawing of a shaft seal device of the present invention. 
         [0044]      FIG. 7(   b ) is a cross-section of a shaft seal device of the present invention. 
         [0045]      FIG. 7(   c ) is a cross-section of a shaft seal device of the present invention. 
         [0046]      FIG. 8  is a cross-sectional drawing of a shaft seal device assembled in vertical submerged pump of the present invention. 
         [0047]      FIG. 9(   a ) is a schematic drawing of a low liquid level operation of the present invention. 
         [0048]      FIG. 9(   b ) is a schematic drawing of a normal liquid level operation of the present invention. 
         [0049]      FIG. 9(   c ) is a schematic drawing of a back-flush liquid of the present invention. 
         [0050]      FIG. 10(   a ) is a schematic drawing of a diffuser blade of the present invention. 
         [0051]      FIG. 10(   b ) is a perspective drawing of the diffuser blade of the present invention. 
         [0052]      FIG. 10(   c ) is another cross-sectional drawing of a diffuser blade of the present invention. 
         [0053]      FIG. 11  is a cross-sectional drawing of a diffuser hole of the present invention.