Abstract:
A sleeve mountable on a rotatable shaft and configured to form a non-contacting seal with a seal ring surrounding and radially spaced from the sleeve, the sleeve including a radially inner surface configured to be mounted on the rotatable shaft, a radially outer surface, an axially inner surface between the radially inner surface and the radially outer surface, an axially outer surface between the radially inner surface and the radially outer surface and a bore configured to provide fluid communication between gas at the axially inner surface of the sleeve and the radially outer surface of the sleeve.

Description:
TECHNOLOGICAL FIELD 
       [0001]    The present disclosure is directed to a sleeve configured for use in a non-contacting gas seal and toward a gas seal including the sleeve, and, more specifically, toward a sleeve configured for use in a non-contacting gas seal that includes a bore configured to carry gas from a high pressure side of the sleeve to a radially outer side of the sleeve and to a gas seal including the sleeve. 
       BACKGROUND 
       [0002]    Various devices are known for forming a seal between a sleeve fixedly mounted on a rotatable shaft and a housing or other structure surrounding the shaft. One type of seal, sometimes referred to as a non-contact circumferential shaft seal, or non-contact gas seal, is effective in controlling leakage. Such seals include one or more seal rings with circumferential inner faces that are spaced a small distance away from the sleeve. Such seals may be formed from compacted and sintered carbon graphite to provide heat and wear resistance, and they are often formed as a plurality of inter-connectable ring segments to facilitate installation around the sleeve. The seal rings are held in place by a suitable retaining device and may include a biasing device, such as a circumferential or garter spring, for holding the seal segments together. 
         [0003]    It is desirable to make the gap between the sleeve and seal ring as small as practicable while substantially preventing the sleeve from contacting the seal ring. To this end, it is known to provide cutouts or pads on the radially inner face of the seal ring in order to generate lift relative to the sleeve and maintain a cushion of gas that helps keep the seal ring away from the sleeve. Various arrangements are also known for routing gas around the outer walls of the seal ring to keep the seal ring in a particular axial location and to maintain a radial spacing from the sleeve. 
       SUMMARY 
       [0004]    The present disclosure provides an improved gas seal and arrangement for maintaining a radial spacing between a seal ring and a sleeve mounted on a rotatable shaft inside the sleeve. To this end, a first aspect of the disclosure comprises a sleeve mountable on a rotatable shaft that is configured to form a non-contacting seal with a seal ring surrounding and radially spaced from the sleeve. The sleeve includes a radially inner surface configured to be mounted on the rotatable shaft, a radially outer surface, an axially inner surface between the radially inner surface and the radially outer surface, and an axially outer surface between the radially inner surface and the radially outer surface. The sleeve also includes a bore configured to provide fluid communication between gas at the axially inner surface of the sleeve and the radially outer surface of the sleeve. 
         [0005]    Another aspect of the disclosure comprises a non-contacting gas seal that includes the sleeve described above, and a seal ring having a radially inner side extending around the radially outer surface of the sleeve, a radially outer side, an axially inner side and an axially outer side. 
         [0006]    A further aspect of the disclosure comprises a sleeve mountable on a rotatable shaft and configured to form a non-contacting seal with a seal ring radially spaced from the sleeve. The sleeve includes a radially inner surface configured to be mounted on the rotatable shaft, a radially outer surface, an axially inner surface between the radially inner surface and the radially outer surface, and an axially outer surface between the radially inner surface and the radially outer surface. The sleeve also includes pressure generating means for increasing a pressure between the sleeve and the seal ring radially spaced from the sleeve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    These and other aspects and features of the present disclosure will be better understood after a reading of the following detailed description together with the attached drawings. 
           [0008]      FIG. 1  is an exploded perspective view of a seal that includes a sleeve mountable on a rotatable shaft and a seal ring that surrounds the sleeve. 
           [0009]      FIG. 2  is a perspective view of the seal ring of  FIG. 1 . 
           [0010]      FIG. 3  is a perspective view of the sleeve of  FIG. 1 . 
           [0011]      FIG. 4  is a partial sectional view of the sleeve of  FIG. 3  taken along line IV-IV in  FIG. 3 . 
           [0012]      FIG. 5  is side elevational view of the sleeve of  FIG. 1 . 
           [0013]      FIG. 6  is a top plan view of the sleeve of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring now to the drawings, wherein the showings are for the purpose of illustrating presently preferred embodiments of the disclosure only and not for limiting same,  FIG. 1  shows a non-contact gas seal  10  comprising a sleeve  12  and a seal ring  14 . The sleeve  12  is configured to be mounted on a rotatable shaft (not illustrated), and the sleeve  12  includes a radially inner surface  16 , a radially outer surface  18 , an axially inner surface  20  and an axially outer surface  22 . The terms “inner” and “outer” are used herein with reference to the high pressure space that is to be sealed by the gas seal  10 ; the “inner” side of the gas seal  10  is the high pressure side of the gas seal, the inside of a compressor, for example, and the outer side of the gas seal  10  is a housing of the compressor or the environment around the device in which the gas seal  10  is installed. These terms are used for ease of reference, and the “inner” side of the seal is the side intended to face a higher pressure environment even if in some cases that high pressure environment might not be described as being “inside” something else. 
         [0015]    The axially inner surface  20  includes a plurality of recesses  24  that extend into the axially inner surface  20  from the radially outer surface  18 . Each of these recesses includes a bottom  26  which faces in a generally axial direction and may or may not be parallel to the axially inner surface  20 , and a side wall  28  that extends from the bottom  26  to the axially inner surface  20 . The side wall  28  has a first portion  30  that is linear and a second portion  32  that is curved, and the side wall  28  meets the bottom  26  at a junction  34 . The shape of the side wall  28  is configured to increase a pressure in the recess  24  when the sleeve  12  rotates. Therefore, other recess shapes could be used without exceeding the scope of the present disclosure. 
         [0016]    The radially outer surface  18  of the sleeve  12  includes a circumferential groove  36  that extends completely around the sleeve  12 . The groove may be discontinuous in other embodiments. A bore  38  extends from the bottom  26  of each of the recesses  24  to a location on the radially outer surface  18  of the sleeve  12 . In the present embodiment, the second end of the bore  38  is located in the groove  36 . Moreover, as will be appreciated from  FIGS. 4 and 6 , the bore  38  preferably tapers in the direction from the axially inner surface  20  to the radially outer surface  18 . While a tapered bore  38  is presently preferred, it may be possible to use a constant-diameter bore in other embodiments. The bore  38  has a first end  40  near the junction  34  of the recess bottom  26  and the second, curved portion  32  of the recess side wall  28  and a second end  42  in the groove  36 . The second end  42  of the bore  38  is offset from the first end  40  of the bore in axial, radial and circumferential directions, and the bore  38  thus extends at an angle to the axis of rotation of the sleeve (i.e., it is not parallel or perpendicular to the axis of rotation). In some embodiments, the groove  36  and/or the recesses  24  may be omitted such that the bore  38  will extend from the axially inner surface  20  to the radially outer surface  18 . Also, as used herein, the bottoms  26  of the recesses  24  may also be considered to be part of the axially inner surface  20 . 
         [0017]    Turning now to the seal ring  14  illustrated in  FIGS. 1 and 2 , the seal ring  14  includes a radially inner side  46 , a radially outer side  48 , an axially inner side  50  and an axially outer side  52 . The seal ring  14  itself is formed from three (or more) separate seal ring segments  14   a,    14   b  and  14   c  which segments allow for the radially installation of the seal ring  14  in a housing (not illustrated) or around the sleeve  12 . The radially inner side  46  and the axially outer side  52  also include cutouts  54  that contribute to hydrostatic and/or hydrodynamic balancing of the seal ring  14  relative to the sleeve  12 . A bore  56  extends from the radially inner side  46  of the seal ring  14  to the axially outer side  52  of the seal ring  14 . A first end  58  of the bore  56  is located between a pair of adjacent cutouts  54  in the radially inner side  46  of the seal ring  14  and a second end  60  of the bore  56  is located in or between a pair of the cutouts  54  in the axially outer side  52 . The bore  56  is generally axially centered on radially inner side  46  and radially centered on the axially outer side  52  and may be straight or curved but, for ease of manufacture, may also comprise a first radial portion leading away from the first end  58  and a second axial portion leading away from the axially outer side  52  which first and second portions meet at a right angle inside the seal ring. 
         [0018]    The operation of the gas seal  10  is now described. The sleeve  12  is installed on a rotatable shaft (not illustrated) and the seal ring  14  is installed in a housing (not illustrated) around the sleeve  12  so that a very small space (on the order of 2 to 8 micrometers) exists between the sleeve  12  and the seal ring  14 . Pressure is increased on the side of the gas seal  10  where the axially inner surface  20  of the sleeve  12  and the axially inner side  50  of the seal ring  14  are located, and even if the sleeve  12  is not rotating relative to the seal ring  14 , gas escapes through the gap between the sleeve  12  and the seal ring  14  and also through the bore  38 . When the shaft and sleeve  12  begin to rotate, the rotation of the sleeve  12  in combination with the angle made by the bore  38  relative to the axis of rotation, forces high pressure gas into the bore  38 . The taper of the bore  38  increases the pressure of the gas in the bore  38 , and a relatively high pressure jet of gas exits the second end  42  of the bore  38  between the radially outer surface  18  of the sleeve and the radially inner side  46  of the seal ring  14 . When the groove  36  is present, the groove  36  may help to distribute the gas around the circumference of the sleeve  12  and/or equalize the radially outward pressure produced by the plurality of bore second ends  42  in the groove  36 . This outward flow of high pressure gas helps form a buffer between the sleeve  12  and the seal ring  14  and helps to maintain the position of the seal ring  14  relative to the sleeve  12 . 
         [0019]    The second ends  42  of the bores  38  in the axially outer surface  22  of the sleeve  12  are axially aligned with the first ends  58  of the bores  56  in the axially inner side  50  of the seal ring  14 , and thus some of the gas exiting the second ends  42  of the bores  38  will enter the first ends  58  of the bores  56  and exit the second ends  60  of the bores  56  in the axially outer side  52  of the seal ring  14 . The bores  56  in the seal ring  14  generally have a larger diameter than the diameter of the bore  38  in the sleeve  12 . 
         [0020]    The diameter of the bore  38  in the sleeve and the amount of its taper and the angle that the bore  38  makes relative to the axis of rotation of the sleeve  12  can be adjusted based on the application in which the gas seal  10  is being used, i.e., based on the pressure difference expected between the high and low pressure sides of the gas seal  10  and on the speed at which the sleeve  12  is expected to rotate relative to the seal ring or gas being compressed. Likewise, the gap between the sleeve  12  and the seal ring  14  and the depth and width of the groove  38  and the diameter of the bore  56  in the seal ring  14  can be selected based on the particular application. 
         [0021]    The present invention has been described herein in terms of a presently preferred embodiment. However, modifications and additions to this embodiment will become apparent to persons of ordinary skill in the art upon a reading of the foregoing disclosure. It is intended that all such modification sand additions form a part of the present invention to the extent they fall within the scope of the several claims appended hereto.