Abstract:
A seal assembly for a turbomachine includes a seal ring rotatable between a first position and a second position and having a plurality of tunnels. Also included is a back ring located adjacent the seal ring and having a plurality of apertures that align with more of the plurality of tunnels of the seal ring when at the second position than at the first position. Further included is a retention piece operably connecting the seal ring and the back ring.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to turbomachines, and more particularly to a seal assembly for turbomachines. 
         [0002]    In various types of turbomachines, seals are employed to provide numerous functions in conjunction with several components within the turbomachine. One such type of seal is a non-contacting face seal that typically operates at a clearance of a few mils (thousandths of an inch) or less. While providing functional advantages such as small leakage, reduced wear and being insensitive to radial runouts, inefficiencies persist. Due to several factors, including manufacturing tolerances and errors, for example, hydrodynamic or hydrostatic features that provide opening forces may be rendered inadequate, which may then lead to self-feeding rub between turbomachine components and undesirable system consequences associated therewith. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    According to one aspect of the invention, a seal assembly for a turbomachine includes a seal face on a seal ring rotatable between a first position and a second position and having a plurality of tunnels. Also included is a back ring located adjacent the seal ring and having a plurality of apertures that align with more of the plurality of tunnels in the seal ring when at the second position than when at the first position. Yet further included is a retention piece operably connecting the seal ring and the back ring. 
         [0004]    According to another aspect of the invention, a seal assembly for a turbomachine includes a relatively circular seal face. Also included is a seal ring rotatable between a first position and a second position and having a plurality of tunnels. Further included is a back ring located adjacent the seal ring and having a plurality of apertures. At least one of the plurality of tunnels is open to the relatively circular seal face at an end and covered by the back ring at another end when the seal ring is at the first position. Yet further included is a retention piece operably connecting the seal ring and the back ring, wherein the seal ring is rotatable relative to the back ring. 
         [0005]    According to yet another aspect of the invention, a seal assembly for a turbomachine includes a relatively circular seal face. Also included is a seal ring rotatable between a first position and a second position, and having a plurality of tunnels. Further included is a back ring located adjacent the seal ring and having a plurality of apertures, wherein the back ring is configured to cover at least one of the plurality of tunnels when the seal ring is in the first position, at least one of the plurality of apertures uncovering a tunnel in the second position. Yet further included is a retention piece operably connecting the seal ring and the back ring, wherein the seal ring is rotatable relative to the back ring. 
         [0006]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  is a side elevational view of a seal system; 
           [0009]      FIG. 2  is a perspective view of a seal assembly; 
           [0010]      FIG. 3  is a perspective view of a retention piece having a securing pin; 
           [0011]      FIG. 4  is a perspective view of a back ring secured by the retention piece; 
           [0012]      FIG. 5  is a perspective view of a seal ring operably coupled to the back ring; 
           [0013]      FIG. 6  is a front elevational view of the seal ring in a first position; and 
           [0014]      FIG. 7  is a front elevational view of the seal ring in a second position. 
       
    
    
       [0015]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Referring to  FIG. 1 , illustrated is a seal system  1  for use within a turbomachine (not shown), such as a turbine system and includes a rotor face  51  on a rotor  50 , a seal assembly  10  including a seal ring  12 , a back ring  14  and a seal face  16 . The seal assembly  10  also includes a retention piece  18  that is attached to or is part of stationary component. An anti-rotation component  20  which is fixed to the retention piece  18  to prevent the seal ring  12  and the back ring  14  from rotating, while allowing them to move axially. A spring  19  is used to bias the seal ring  12  away or toward rotor face  51 . The seal assembly  10  also includes a secondary seal  17  that prevents leakage between seal ring  12  and retention piece  18 , and meanwhile allows the seal ring  12  to slide axially. The seal ring  12  includes a plurality of tunnels  42  that feed working fluid into the seal face  16 . The back ring  14  consists of apertures  30  that coincide with some of the tunnel  42  openings at the design condition. When there is a rub between seal face  16  and the rotor face  51 , the friction torque will force the seal ring  12  to rotate a predetermined amount to the hard stop. Meanwhile, the back ring  14  is not rotated. At the after-rotation position, more tunnel  42  openings coincide with the apertures  30  on the back ring  14 . Therefore, more tunnels  42  are exposed to high-pressure working fluid that increases fluid pressure on the seal face  16 . The increased pressure pushes the seal ring  12  away from rotor surface  51  and lets the seal system  1  operate at a larger clearance. Such a fail-safe design enables the seal system  1  to avoid further damage of the seal face  16  if rubbing occurs. 
         [0017]    Referring to  FIG. 2 , the seal assembly  10  may be employed at various regions within the turbomachine and may be associated with various components within the turbomachine, and particularly between a high pressure region and a low pressure region (relative to one another). In such an application, the seal assembly  10  is relatively circular, and is disposed to at least partially surround the rotor  50  and provide sealing in desirable locations. The seal assembly  10  is a non-contacting seal assembly that operates with a clearance of less than approximately ten (10) mils (thousandths of an inch) from the rotor face  51 . The fail-safe design allows the seal system  1  to operate at a close clearance in a reliable manner. 
         [0018]    Referring to  FIG. 3 , a portion of the retention piece  18  is disposed adjacent to the seal face  16  and may be indirectly coupled to the seal ring  12  rear end by the spring  19 . The retention piece  18  includes a securing pin  20  that extends axially forward toward the seal face  16 . As described above, the seal assembly  10  may be employed in various regions of the turbomachine and at various orientations, however, in the illustrated examples and for the purpose of this description, the seal assembly  10  is oriented proximate an outer surface of the rotor  50  of the aforementioned turbine assembly. 
         [0019]    Referring to  FIG. 4 , the back ring  14  includes a pin receiving through-hole  22  that receives the securing pin  20  for anti-rotation purposes in a mating manner. The back ring  14  includes a base portion  23  that extends circumferentially in a substantially circular or elliptical path and the plurality of apertures. Those plurality of apertures  30  can be closed holes or open gaps between fingers  28 , which may comprise simply a plate. It is contemplated that suitable alternative geometric configurations may be suitable to form the plurality of apertures  30  on the back ring  12 . 
         [0020]    Referring to  FIG. 5 , the seal ring  12  is disposed adjacent to, and axially forward of, the back ring  14 . The seal ring  12  includes a fuse-type connection with the retention piece  18 , such as a breakaway slot  32  that receives the securing pin  20  in a mating manner. In contrast to the back ring  14 , which includes a pin receiving through-hole  22  that securely and rigidly prevents the back ring  14  from rotating by the retention piece  18 , and therefore the seal face  16 , the seal ring  12  is rotatable relative to the back ring  14  and the retention piece  18  within the length of breakaway slot  32 . Rotation of the seal ring  12  may occur for numerous reasons, such as rubbing of the rotor  50  during operation, for example. 
         [0021]    The breakaway slot  32  is comprised of at least two segments, a first receiver  34  and a second receiver  36 . Both the first receiver  34  and the second receiver  36  are of sufficient diameter to surround the securing pin  20 . The first receiver  34  and the second receiver  36  are separated by a thin band or a top detent  38  and a bottom detent  40 . Irrespective of the separation structure between the first receiver  34  and the second receiver  36 , the structural and/or frictional force imparted by the separation structure is sufficient to maintain the positioning of the securing pin  20  within either the first receiver  34  or the second receiver  36 , up to a certain rotational torque. A torque exerted on the seal ring  12 , such as the rubbing of the rotor  50  previously described, that is sufficient to impart rotation of the seal ring  12  will cause the seal ring  12  to overcome the frictional and/or structural force between the securing pin  20  and the first receiver  34  or second receiver  36 . The torque that is sufficient to overcome the forces is dependent upon the application of use and may be modified as needed by altering the separation structure between the first receiver  34  and the second receiver  36 . 
         [0022]    In another embodiment, the fuse-type connection can be a pin on the seal ring  12  and a breakaway slot  32  on the retention piece  18 . Yet in another embodiment, the pin can be designed to be sheared upon rotor rubbing as the sacrifice feature, instead of the band in the breakaway slot  32 . 
         [0023]    Referring to  FIGS. 6 and 7 , the seal ring  12  includes the plurality of tunnels  42  that extend axially through the seal ring  12 . In a first position, corresponding to positioning of the securing pin  20  within the first receiver  34  of the breakaway slot  32  of the seal ring  12 , at least one of the plurality of tunnels  42  of the seal ring  12  is covered on the axial rearward face of the seal ring  12  by the plurality of fingers  28  of the back ring  14 . The number and position of the plurality of tunnels  42  is adjustable and may be modified for particular applications. Relatedly, the number and shape of the plurality of fingers  28  may be modified to provide the desired function that is determined by how many of the plurality of tunnels  42  are covered. 
         [0024]    As described above, the seal ring  12  is rotatable relative to the back ring  14 , such rotation occurring upon introduction of a force on the seal ring  12 . Also previously described, such a force may cause the seal ring  12  to impart a torque sufficient to drive the securing pin  20  from the first receiver  34  of the breakaway slot  32  to the second receiver  36  of the breakaway slot, or vice versa. Upon moving from the first position to the second position, where the securing pin  20  is in the second receiver  36 , additional plurality of tunnels  42  of the seal ring  12  are uncovered by the back ring  14 , and specifically the plurality of fingers  28  of the back ring  14 . To assist in facilitation of the uncovering of the plurality of tunnels  42 , each of the plurality of fingers  28  includes at least one aperture  30  to correspond to one of the plurality of tunnels  42  when the seal ring  12  is disposed in the second position, as illustrated in  FIG. 6 . 
         [0025]    Uncovering of some or all of the plurality of tunnels  42  advantageously allows high pressure air to flow through the plurality of tunnels  42  and separate the seal ring  12  from the seal face  16 , or any other adjacent structure, such as a bearing. Such a seal assembly  10  reduces the likelihood of seal rub. 
         [0026]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.