Abstract:
A segmented labyrinth seal assembly and method according to which a plurality of arcuate segments extend around a rotating shaft with the shaft being engaged by a sealing portion of each segment, thus sealing against the movement of fluid in an axial direction along the shaft. An engagement member extends from one end of at least one segment and is adapted to engage the corresponding end of the adjacent segment. The engagement member is urged in a direction towards the corresponding end to apply a separation force between the ends, and the separation force is adjustable.

Description:
BACKGROUND  
         [0001]    The present disclosure relates, in general, to a seal assembly and method and, more particularly, to a segmented labyrinth seal assembly and method for sealing against the leakage of fluid.  
           [0002]    Segmented labyrinth seal assemblies are often used to seal against the leakage of fluid in applications involving a rotating shaft that penetrates a fixed casing such as in turbo machine, centrifugal compressor, and the like. These type of seal assemblies usually include a series of arcuate labyrinth segments disposed in an end-to-end relationship and together extending around the rotating shaft with minimal clearance. The segments are adapted to expand during light loads or sudden loss of load to minimize rubbing damage caused by misalignment, vibration and thermal distortion.  
           [0003]    However, these assemblies are often difficult to assemble, do not necessarily provide uniform loading on all segments, and are difficult or impossible to adjust.  
           [0004]    Therefore, what is needed is a segmented seal assembly of the above type that is relatively easy to assembly, provides uniform loading on all segments of the assembly and can easily be adjusted.  
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a partial elevation-partial sectional view of a segmented labyrinth seal assembly according to an embodiment of the present invention.  
         [0006]    [0006]FIG. 2 is an enlarged cross-sectional view taken along the line  2 - 2  of FIG. 1.  
         [0007]    [0007]FIG. 3 is a partial cross-sectional view, depicting a component of the seal assembly of FIGS. 1 and 2.  
         [0008]    [0008]FIG. 4 is a view, similar to FIG. 3 but depicting an alternate embodiment of the component of FIG. 3. 
     
    
     DETAILED DESCRIPTION  
       [0009]    An embodiment of the present invention is shown in FIG. 1 in connection with a shaft  10  forming a portion of a turbo machine, centrifugal compressor, or the like. An annular labyrinth seal assembly  12  extends around the shaft to seal against the leakage of fluid in an axial direction along the shaft from a high pressure area to a low pressure of the turbo machine. The seal assembly  12  consists of four arcuate segments  14 ,  16 ,  18  and  20  disposed in an end-to-end relationship with each segment extending for approximately ninety degrees to form a ring. A portion of the outer surfaces of the segments  14 ,  16 ,  18 , and  20  are machined to form flat surface portions  14   a ,  16   a ,  18   a , and  20   a , midway between the respective ends of each segment.  
         [0010]    A spring-loaded assembly  24  is mounted in one end portion of the segment  14  and engages the corresponding end of the segment  20 ; a spring-loaded assembly  26  is mounted in one end portion of the segment  16  and engages the corresponding end of the segment  14 ; a spring-loaded assembly  28  is mounted in one end portion of the segment  18  and engages the corresponding end of the segment  16 ; and a springloaded assembly  30  is mounted in one end portion of the segment  20  and engages the corresponding end of the segment  18 . The assemblies  24 ,  26 ,  28 , and  30  will be described in detail later.  
         [0011]    With reference to FIG. 2, the seal assembly  12  is mounted in a casing  32 , and although shown partially, it is understood that the casing extends completely around the shaft  10  and supports it for rotation in a conventional manner. The casing  32  has an internal cylindrical bore  32   a  which receives the shaft  10 , and an inner annular cavity, or enlarged groove,  32   b  formed in the inner surface portion of the casing that defines the bore  32   a , for receiving the seal assembly  12 . Although FIG. 2 depicts only the seal assembly segment  18  extending in the cavity  32   b , it is understood that the other segments  14 ,  16 , and  20  also extend in other portions of the cavity.  
         [0012]    The outer surface of the shaft  10  is radially spaced from the corresponding inner surface of the casing  32  to form an annular chamber  34 . The segment  18  has an annular inside labyrinth surface  18   b  extending through a corresponding portion of the chamber  34  and into a sealing engagement with the outer surface of the shaft  10 . The labyrinth surface  18   b  thus divides the chamber  34  into a relatively high pressure portion  34   a  located upstream of the labyrinth surface  18   b  and a relatively low pressure portion  34   b  located downstream of the labyrinth surface. In the event the casing  32  forms part of a turbo machine or a compressor, the high pressure chamber portion  34  typically would be in pressure communication with the high pressure discharge gas from the impeller (not shown) of the turbo machine or compressor.  
         [0013]    The inner surface of the segment  18  is spaced from the inner wall of the cavity  32   a  to form a annular space, and a passage  36  connects the space with the chamber portion  34   a . Thus, the relatively high pressure in the chamber portion  34   a  is transmitted to the latter space so that as the pressure increases, the segment  18 , and therefore its labyrinth surface  18   b , is forced into sealing engagement with the outer surface of the shaft  10 . This establishes a seal against the movement of the high pressure gas in an axial direction along the shaft  10  from the chamber portion  34   a  to the chamber portion  34   b.    
         [0014]    It is understood that the other segments  14 ,  16 , and  20  of the seal assembly are identical to the segment  18 , extend in the cavity  32   a  of the casing in the same manner, and, together with the segment  18 , surround the entire outer surface of the shaft  10 . Also, each of the other segments  14 ,  16 , and  20  has a labyrinth surface that also sealing engages the outer surface of the shaft  10  in the same manner as described above.  
         [0015]    Since the specific arrangement of the segments  14 ,  16 ,  18  and  20 , the labyrinth surface  18   b  and the corresponding labyrinth surfaces of the segments  14 ,  16 , and  20 , as well as their engagement with the shaft  10 , do not, per se, form a part of any embodiment of the present invention, they will not be described in any further detail. However, they are fully disclosed in U.S. Pat. No. 5,403,019, assigned to the present assignee, and the disclosure of this patent is incorporated by reference.  
         [0016]    Although the casing  32  is not shown in FIG. 1 for the convenience of presentation, it is provided with two stops  38   a  and  38   b  in its upper half, which are shown in FIG. 1. The labyrinth segments  14 ,  16 ,  18 , and  20  slide into the cavity  32   a  of the casing  30  and are retained by the stops  38   a  and  38   b  extending in corresponding grooves formed in the end portions of the segments  14  and  20 .  
         [0017]    Referring to FIGS. 1 and 3, a through bore  20   b  is formed through the segment  20  and extends from an outer surface of the segment to the end thereof adjacent the corresponding end of the segment  18 . The spring-loaded assembly  30  is located in the bore  20   b  and includes a spring  40  extending in the bore between a spring plate  42  and a ball  44 . A portion of the ball  44  extends outwardly from the bore  20   b  under the force of the spring  40 , and the remaining portion of the ball rides in a retainer sleeve  46  disposed in the end portion of the bore. The spring  40  thus urges the ball  44  outwardly from the bore  20   b  against the corresponding end of the adjacent segment  18 .  
         [0018]    A portion of the bore  20   b  extending from the surface of the segment  20  is of a smaller diameter than the remaining portion of the bore to form a shoulder for receiving the spring plate  42 . The smaller-diameter portion of the bore  20   b  is internally threaded, and an externally threaded set-screw  48  is in threaded engagement with this bore portion. Thus, rotation of the set-screw  48  causes corresponding axial movement of same in the bore  28   b  and thus adjusts the compression on the spring  40 , and therefore the force applied by the spring to the ball  44 . This creates an adjustable separation force between the end of the segment  20  and the corresponding end of the segment  18 .  
         [0019]    The connection assemblies  24 ,  26  and  28  are identical to the assembly  30  and are mounted in the seal assembly segments  14 ,  16 , and  18 , respectively, in an identical manner.  
         [0020]    In operation, the set-screw  48  is adjusted to apply a predetermined separation force between the segments  18  and  20  as discussed above, and the set-screws associated with the segments  14 ,  16 , and  20  are adjusted in the same manner. Thus, the segments  14 ,  16 ,  18 , and  20  are spring loaded into a slightly expanded position, with the corresponding ends of adjacent segments being in a slightly spaced condition, as shown in FIG. 1. As the pressure in the chamber portion  34   a  pressure increases, the labyrinth surface  18   a  of the segment  18 , as well as the labyrinth surfaces of the segments  14 ,  16 , and  20  will be forced into a sealing engagement with the shaft  10  as described above.  
         [0021]    The seal assembly  10  has several advantages. For example, it is relatively easy to assemble, provides uniform loading on all segments of the assembly and can easily be adjusted. Also, the flat surface portions  14   a ,  16   a ,  18   a , and  20   a  make the segments  14 ,  16 ,  18 , and  20 , respectively, more stable when retracted and ensures that the upstream pressurized steam gets into the cavity  32   a  and into the annular space between the inner wall of the cavity and the corresponding outer surface of each segment  14 ,  16 ,  18 , and  20 .  
         [0022]    According to the embodiment of FIG. 4 the ball  44  of the previous embodiment is replaced by a solid cylindrical plunger  50 . Since the remaining components of the embodiment of FIG. 4 are identical to the embodiment of FIGS.  1 - 3 , they are referred to by the same reference numerals.  
         [0023]    An annular flange  50  is formed on the plunger near one end thereof which receives the corresponding end of the spring  40 . A portion of the plunger  50  extends outwardly from the bore  20   b  under the force of the spring  40 , and the spring extends around another portion of the plunger in the bore  20   b . The spring  40  thus urges the plunger  50  outwardly from the bore  20   b  against the corresponding end of the adjacent segment  18 . It is understood that a plunger, identical to the plunger  50 , are provided on the connection assemblies  24 ,  26  and  28  and function in an identical manner. The embodiment of FIG. 4 thus enjoys all of the advantages of the embodiment of FIGS.  1 - 3 .  
         [0024]    It is understood that several variations may be made in the foregoing without departing from the scope of the invention. For example, number of segments forming the ring around the shaft can vary within the scope of the invention. Also, the spatial references, such as “above”, etc. is for the purpose of example only, are not intended to limit the structure disclosed to a particular orientation. Moreover, the embodiment described above is not limited to turbo machines or compressors, but is equally applicable to other equipment requiring a seal.  
         [0025]    Other modifications, changes and substitutions are intended in the foregoing disclosure and in some instances some features of the disclosure will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure.