Abstract:
A turbo-machine including a volute casing, a rotating shaft, an impeller, seals, an axial thrust control member and a bellows unit. The volute casing defines therein a fluid passage. The rotating shaft is rotatably provided in the volute casing. The impeller is coupled to the rotating shaft to draw fluid using centrifugal force. The seals are provided around the front and rear ends of the impeller to prevent leakage of fluid. The axial thrust control member is installed in the volute casing behind the impeller. The bellows unit includes the piston installed in the volute casing in a shape surrounding a circumferential outer surface of the axial thrust control member; and a bellows connected with one surface of the piston, the bellows having the predetermined elasticity; and an internal space, between the piston and the volute casing, isolated from the fluid drawn behind the impeller.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to centrifugal turbo-machines and, more particularly, to a centrifugal turbo-machine in which an axial thrust control member is configured to automatically control axial thrust generated by a difference between static pressures of front and rear ends of an impeller provided in a centrifugal pump or compressor, thus appropriately controlling axial thrust even if the axial thrust varies attributable to abnormal operation conditions. 
     2. Description of the Related Art 
     Generally, a centrifugal turbo-machine is a machine which applies kinetic energy (dynamic pressure) to fluid using reaction induced by rotation of an impeller and converts it into pressure energy (static pressure). A centrifugal pump, a centrifugal compressor or the like is a representative example of the centrifugal turbo-machine. 
       FIG. 1  is a sectional view showing the construction of a centrifugal turbo-machine  10  according to a conventional technique. 
     Referring to  FIG. 1 , the conventional centrifugal turbo-machine  10  which converts kinetic energy applied to fluid into pressure energy includes a rotating shaft  12 , an impeller  13 , a volute casing  11  and seals  14  and  15 . The rotating shaft  12  is rotatably installed in the volute casing  11  and supported by a bearing  16 . 
     The impeller  13  is fastened to the rotating shaft  12  and rotates along with the rotating shaft  12 . The impeller  13  draws fluid using centrifugal force generated by rotation thereof. 
     The volute casing  11  defines therein a space into which fluid drawn by the impeller  13  flows. In the volute casing  11 , dynamic pressure of drawn fluid is converted into static pressure. In other words, in the volute casing  11 , kinetic energy of drawn fluid is converted into pressure energy. 
     The seals  14  and  15  reduce the amount of leakage of drawn fluid to increase the efficiency of the centrifugal turbo-machine  10 . The seals  14  and  15  are positioned corresponding to the front and rear ends of the impeller  13 . 
     The operation of the conventional centrifugal turbo-machine  10  having the above-mentioned construction will be explained below. 
     The impeller  13  rotates in the hermetically sealed volute casing  11  to draw fluid into the volute casing  11 . Then, centrifugal force is generated by the impeller  13 . Fluid is drawn into the volute casing  11  by the centrifugal force of the impeller  13 . While the drawn fluid flows into the volute casing  11 , dynamic pressure of fluid is converted into static pressure in the volute casing  11 , thus producing pressure energy. 
     However, some of fluid drawn by the impeller  13  flows through gaps between the surface of the impeller  13  and the seals  14  and  15  rather than being drawn into the volute casing  11 . Fluid passing through the gaps defined by the seals  14  and  15  differ in pressure from each other, thus generating axial thrust. 
     As shown in  FIG. 1 , the shapes of the front and rear ends of the impeller  13  differ from each other and the area of the gap between each end of the impeller  13  and its surrounding casing also have difference. Thus, pressures formed around the front and rear ends of the impeller  13  differ from each other. Furthermore, pressures around outlets of the seals  14  and  15  differ from each other. Therefore, axial thrust is generated in a direction from the rear end of the impeller  13  towards the front end thereof. 
     This axial thrust is applied to the rotating shaft  12  of the centrifugal turbo-machine  10 . The force applied to the rotating shaft  12  is supported by the bearing  16  coupled to the impeller  13 . 
     Here, in the case where appropriate intensity of axial thrust is applied to the rotating shaft  12 , the bearing  16  can reliably support the rotating shaft  12 . However, if excessive axial thrust is applied to the rotating shaft  12 , the expected lifetime of the bearing  16  is reduced. If it exceeds a limit, the bearing  16  may be damaged. 
     Therefore, to prevent damage of the turbo-machine  10  and increase the lifetime of the bearing  16 , the axial thrust should be successfully controlled. For this, a difference between static pressures applied to the front and rear ends of the impeller  13  must be reduced. 
     In the conventional technique, to reduce a difference between static pressures applied to the front and rear ends of the impeller  13 , the area of gap between the impeller  13  and the volute casing  11  was changed by varying the diameters of the seals  14  and  15  provided around the front and rear ends of the impeller  13 . 
     In detail, the conventional technique has used a method in which the intensity of axial thrust generated around the rear end of the impeller  13  is reduced by increasing the diameter of the seal  15  provided around the rear end of the impeller  13  which typically generates relatively large axial thrust. However, the method of reducing axial thrust by changing the diameter of the seal  15  requires much time and costs in manufacturing the turbo-machine, so that it is not economic. 
     Recently, in an effort to overcome the above problem of poor economy, a method of installing an axial thrust control member for controlling axial thrust in a turbo-machine has been developed. 
       FIG. 2  is a sectional view showing a turbo-machine  20  having an axial thrust control member  30  according to a conventional technique. 
     Referring to  FIG. 2 , the turbo-machine  20  having the axial thrust control member  30  can more economically control axial thrust, compared to the prior method of changing the diameter of the seal. However, if input values different from the input values it was designed for are applied to the turbo-machine  20  while it is being operated, an operational problem may be induced. Furthermore, there is a disadvantage in that the turbo-machine  20  may not be able to resist abnormal operation circumstances. 
     For example, in the case where a flow rate of fluid drawn into the turbo-machine  20  is less than the flow rate it was designed for, output pressure is increased and a pressure around the impeller  23  is also increased. Thereby, the entire axial thrust applied to the turbo-machine  20  is also increased. 
     Furthermore, if a design of a fluid supply system for operating the turbo-machine  20  is not appropriate or a loss of pressure of the fluid supply system is increased by penetration of foreign substances while the turbo-machine  20  is being operated, a flow rate of fluid drawn into the turbo-machine  20  becomes less than the designed flow rate and the axial thrust applied to the turbo machine  20  is increased. 
     In addition, in the case where the design of the impeller  23  or the volute casing  21  does not correspond to the designed flow rate, there is a probability of an increase in output pressure. This also is a factor of an increase in axial thrust. 
     Moreover, the axial thrust control member  30  cannot automatically control axial thrust while the turbo-machine  20  is being operated. Merely, the height of the rib  31  of the axial thrust control member  30  is determined to a degree capable of reducing axial thrust in consideration of the intensity of axial thrust expected to be generated while the turbo-machine  20  is being operated. Then, pressure of fluid drawn through the rear end of the impeller  23  is reduced by the resistant force of the rib  31 , thus controlling axial thrust. 
     However, to effectively use the axial thrust control member, after a design flow rate of the turbo-machine  20  and output axial thrust are correctly checked, can the turbo-machine  20  be operated. Only then can the generation of expected axial thrust be appropriately controlled. 
     Furthermore, a problem in an increase of axial thrust exceeding an expected value because of the above several reasons cannot be controlled by the axial thrust control member  30 . In this case, in the same manner as the prior turbo-machine  10  having no axial thrust control member, the bearing  26  may be damaged with the result that the lifetime of the turbo-machine is reduced. 
     As such, in the conventional turbo-machine, when pressure around the seals  24  and  25  is increased over an expected value, the axial thrust control member  30  cannot exhibit its intended function. To improve this, a precise measure of axial thrust is indispensably conducted before the machine is operated. If unexpected measurement results are produced, the design of the axial thrust control member  30  must be revised, or it must be newly manufactured or installed. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a turbo-machine in which protruding heights of ribs provided on an axial thrust control member are automatically controlled depending on an intensity of pressure of fluid drawn behind a rear end of an impeller, so that even though excessive axial thrust greater than a value expected when designing the turbo-machine is generated, the axial thrust can be automatically controlled. 
     In order to accomplish the above object, the present invention provides a turbo-machine, including: a volute casing defining therein a fluid passage for forming a fluid pressure; a rotating shaft provided in the volute casing so as to be rotatable; an impeller coupled to one end of the rotating shaft to draw fluid using centrifugal force generated by rotation; seals provided around front and rear ends of the impeller to prevent leakage of the fluid; an axial thrust control member installed in the volute casing behind the impeller with respect to a flowing direction of the fluid, the axial thrust control member having an annular planar shape, with a plurality of ribs provided on one surface of the axial thrust control member facing the flowing direction of the fluid such that portions of the ribs are exposed from the surface of the axial thrust control member to impede rotation of the fluid; and a bellows unit, having a piston surrounding a circumferential outer surface of the axial thrust control member, the piston covering the outer surface of the ribs and a bellows connected with one surface of the piston, the bellows having a predetermined elasticity. 
     The bellows unit is constructed such that the bellows is compressed by pressure of the fluid drawn into the volute casing and the piston automatically moves by a predetermined distance along the axial direction. 
     The axial thrust control member may be constructed such that the ribs are further exposed from the axial thrust control member by a distance corresponding to the distance that the piston moves along the axial direction, thus increasing resistant force of the ribs impeding the rotation of the fluid. 
     The piston may have a sealing member to isolate the internal space defined by the piston and the volute casing from fluid drawn behind the impeller. 
     The bellows unit may be controlled such that a sum of the elastic force of the bellows and a pressure in the internal space is equal to a pressure of the fluid drawn behind the impeller. 
     In the bellows unit, when the pressure of the fluid drawn behind the impeller is increased, the bellows may be automatically compressed and the resistant force of the ribs provided on the axial thrust control member is thus increased, so that the increased pressure of the fluid is reduced until the sum of the elastic force of the bellows and the pressure in the internal space is equal to the pressure of the fluid drawn behind the impeller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a sectional view showing the construction of a centrifugal turbo-machine according to a conventional technique; 
         FIG. 2  is a sectional view showing a turbo-machine having an axial thrust control member, according to another conventional technique; 
         FIG. 3  is a sectional view of a turbo-machine having a bellows unit, according to an embodiment of the present invention; 
         FIG. 4  is a sectional view illustrating an axial thrust control member according to the embodiment of the present invention; 
         FIG. 5  is a sectional and front view illustrating the piston which moves by the elastic force of the bellows and the insert hole which couples with the ribs of the axial thrust control member; 
         FIG. 6  is a front view illustrating the construction of the axial thrust control member according to the embodiment of the present invention; 
         FIG. 7  is a front view and an enlarged view showing the coupling between the axial thrust control member and the bellows unit according to the embodiment of the present invention; 
         FIG. 8  is an enlarged sectional view of the portion A of  FIG. 3  when the bellows unit is not in operation according to the embodiment of the present invention; 
         FIG. 9  is a view corresponding to the sectional view taken along the line B-B′ of  FIG. 7  when the bellows unit is not in operation according to the embodiment of the present invention; 
         FIG. 10  is an enlarged sectional view of the portion A of  FIG. 3  when the bellows unit is in operation according to the embodiment of the present invention; and 
         FIG. 11  is a view corresponding to the sectional view taken along the line B-B′ of  FIG. 7  when the bellows unit is in operation according to the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. The terms and words used in the specification and claims must not be limited to typical or dictionary meanings, but must be regarded as concepts selected by the inventor as concepts which best illustrate the present invention, and must be interpreted as having meanings and concepts adapted to the scope and spirit of the present invention to aid in understanding the technology of the present invention. 
     Therefore, the construction of the embodiment illustrated in the specification and the drawings must be regarded as only one illustrative example, and these are not intended to limit the present invention. Furthermore, it must be understood that various modifications, additions and substitutions are possible at the point of time of application of the present invention. 
     The construction of a turbo-machine having a bellows unit according to the embodiment of the present invention will be described in detail. 
       FIG. 3  is a sectional view of the turbo-machine  100  having the bellows unit  200 , according to the embodiment of the present invention.  FIG. 8  is an enlarged sectional view of the portion A of  FIG. 3  when the bellows unit  200  is not in operation. 
     Referring to  FIGS. 3 and 8 , the turbo-machine  100  according to the embodiment of the present invention includes a volute casing  110 , a rotating shaft  120 , an impeller  130 , seals  140  and  150 , an axial thrust control member  210  and a bellows unit  200 . 
     The functions and operation of the volute casing  110 , the rotating shaft  120 , the impeller  130  and the seals  140  and  150  are the same as those of the corresponding elements of the conventional turbo-machine  20  having the turbo-machine  10  and the axial thrust control member, therefore further explanation is deemed unnecessary. 
       FIG. 4  is a sectional view of an axial thrust control member  210  according to the embodiment of the present invention.  FIG. 5  is a sectional and front view illustrating the piston  213  which moves by the elastic force of the bellows  214  and the insert hole  216  which couples with the ribs of the axial thrust control member  210 .  FIG. 6  is a front view illustrating the construction of the axial thrust control member  210  according to the embodiment of the present invention.  FIG. 7  is a front view and an enlarged view showing the coupling between the axial thrust control member  210  and the bellows unit  200 . 
     Referring to  FIGS. 4 through 7 , the axial thrust control member  210  comprises an annular planar member. A plurality of ribs  211  protrudes from one surface of the axial thrust control member  210  which faces the flow of fluid in order to reduce a difference in static pressure between the front and rear ends of the impeller  130  and thus control axial thrust. 
     Here, the axial thrust control member  210  reduces an angular velocity component of fluid generated by the rotation of the impeller  130  and thus controls pressure around the rear end of the impeller  130 . The effect of pressure control is determined by the shape of the axial thrust control member  210 . 
     Preferably, the height to which each rib  211  protrudes and the number of ribs  211  are determined in consideration of both a flow rate of fluid to be drawn when the turbo-machine  100  is being operated and the intensity of axial thrust to be generated. 
     As the height to which each rib  211  protrudes is increased, the extent of decrease in the pressure of fluid to be drawn is increased. As the height to which each rib  211  protrudes is reduced, the extent of decrease in the pressure of fluid to be drawn is also reduced. 
     Furthermore, as the number of ribs  211  is increased, the amount of decrease in pressure of fluid to be drawn is increased. As the number of ribs  211  is decreased, the extent of decrease in the pressure of fluid to be drawn is also reduced. 
     Meanwhile, the bellows unit  200  includes a piston  213  which has an annular planar shape and surrounds the circumferential outer surface of the axial thrust control member  210  and covers the outer surface of the rib  211  and a bellows  214  which is connected with one surface of the piston and has a predetermined elasticity. 
     Furthermore, rib insert holes  216 , the number of which is the same as that of ribs  211 , are formed in one surface of the piston  213 , so that the ends of the ribs  211  which protrude from the axial thrust control member  210  are respectively inserted into the rib insert holes  216 . 
     The piston  213  has at edges thereof sealing members  215   a  and  215   b  which isolate the internal space  217  from the outside such that the pressure of the internal space  217  is maintained at atmospheric pressure. 
     As such, the pressure inside the piston  213 , that is, the pressure in the internal space  217 , is maintained at atmospheric pressure. The pressure outside the piston  213  varies depending on the pressure of drawn fluid. Therefore, different pressures are applied to the inside and the outside of the piston  213 . 
     With regard to the atmospheric pressure state in the internal space  217 , it is preferable that when the piston  213  is installed in the volute casing  110 , the internal space  217  defined by the piston  213  be sealed in the atmospheric pressure state. However, the present invention is not limited to this. The initial pressure in the internal space  217  may be determined depending on the amount of fluid drawn into the volute casing  110  and the intensity of fluid pressure. 
     In the bellows unit  200 , the bellows  214  is compressed by the pressure of fluid drawn into the volute casing  110  so that the piston  213  moves automatically by a predetermined distance. 
     Furthermore, the ribs  211  of the axial thrust control member  210  are further exposed at heights corresponding to the distance that the piston  213  moves along the axial direction. Thus, force resistant to rotation of fluid by the impeller  130  is increased by the ribs  211 . 
     The operation principle of the turbo-machine  100  having the bellows unit  200  according to the embodiment of the present invention will be described below. 
       FIG. 8  is an enlarged sectional view of the portion A of  FIG. 3  when the bellows unit  200  is not in operation according to the embodiment of the present invention.  FIG. 9  is a view corresponding to the sectional view taken along the line B-B′ of  FIG. 7  when the bellows unit  200  is not in operation according to the embodiment of the present invention.  FIG. 10  is an enlarged sectional view of the portion A of  FIG. 3  when the bellows unit  200  is in operation according to the embodiment of the present invention.  FIG. 11  is a view corresponding to the sectional view taken along the line B-B′ of  FIG. 7  when the bellows unit  200  is in operation according to the embodiment of the present invention. 
     Referring to  FIGS. 8 and 9 , when the turbo-machine  100  of the present invention is in operation within expected design parameters, axial thrust generated is controlled in such a way that the ribs  211  exposed from the surface of the axial thrust control member  210  impede rotation of fluid to reduce an angular speed of the fluid, and further so that static pressure of fluid around the rear end of the impeller  130  rapidly reduces. 
     Here, in the bellows unit  200 , the bellows  214  and the piston move as shown in  FIG. 9  in order that the sum of a pressure P be1  applied to the piston  213  by the bellows  214  and an atmospheric pressure P air  formed in the internal space  217  defined by the piston  213  is equilibrated with a pressure P 1  of fluid drawn behind the rear end of the impeller  130 . 
     In other words, the bellows unit  200  is constructed such that the sum of the elastic force of the bellows  214  provided in the internal space  217  defined by the piston  213  and the pressure in the internal space  217  is the same as the pressure of fluid drawn behind the rear end of the impeller  130 . 
     Meanwhile, in the case where the turbo-machine  100  is operated under unexpected conditions so that the output pressure of the impeller  130  becomes higher than the expected value, as shown in  FIGS. 10 and 11 , the pressure P 2  of fluid drawn behind the rear end of the impeller  130  is also increased (P 2′ &gt;P 1 ). Thereby, the piston  213  automatically moves along the axial direction. Thus, the protruding heights of the ribs  211  of the axial thrust control member  210  are relatively increased. 
     In other words, when the pressure of fluid drawn behind the rear end of the impeller  130  is increased, the piston  213  of the bellows unit  200  automatically moves. Thus, the resistant force of the ribs  211  of the axial thrust control member  210  is increased and the fluid pressure which has been increased is reduced. Therefore the ribs  211  have been relatively increased in height function to reduce the pressure of fluid behind the seal  150  and prevent excessive axial thrust from being applied to a pump rotor. 
     At that time, the bellows  214  is compressed according to the movement of the piston  213  and the elasticity of the bellows increases. Also, the pressure of the internal space  217  increases due to the shrink of the volume. 
     Ultimately, the position of the piston  213  is determined as a position at which the pressure of fluid drawn behind the rear end of the impeller  130  is equilibrated with the sum of the elastic force of the bellows  214  and the pressure in the internal space  217  (P 2 =P be2 +P air′ , P 2 &lt;P 2′ ). 
     As such, even in unexpected conditions, the turbo-machine  100  can automatically control the axial thrust. Therefore, the present invention can be free from a problem pertaining to the axial thrust which limits the design of the turbo-machine  100 . Furthermore, by virtue of the automatic control of the axial thrust, the lifetime of the bearing  160  of the turbo-machine  100  can be increased. 
     As described above, in the turbo-machine according to the present invention, a bellows unit can automatically reduce a difference in static pressure of drawn fluid depending on the intensity of pressure of the fluid. Therefore, the turbo-machine can be more reliably and smoothly operated. 
     Furthermore, because axial thrust can be automatically controlled, damage of elements, such as a bearing, etc., can be prevented. Thus, the durability of the turbo-machine can be enhanced. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.