as summarized above , the invention provides a seal at the intersegments of the hydrogen seal rings for preventing oil leakage through this potential gap between the seal ring segments . the improved seal rings 112 of the invention are adapted to be disposed in a seal casing as described above with reference to fig2 . accordingly , that figure has been annotated to include reference number 112 to illustrate the disposition of the improved seal rings 112 and to the extent that it corresponds to the conventional assembly , a description of the seal assembly incorporating the improved seal rings 112 , will not be provided here . as shown in fig3 a brush seal 52 is made by sandwiching bristles 54 between two metal plates 56 and orienting the sandwiched bristles at an angle of about 90 ° to the surface with which it forms a seal . typically , the bristle diameter ranges from about 0 . 002 to about 0 . 01 inch , depending on the bristle material ( metal or non - metal ), temperature , pressure and operating condition ( static or dynamic ). the bristles are fabricated either by brazing / welding for metal bristles or gluing for nonmetal bristles . from fig3 it can be observed that at the lower part of the brush , a space 58 is left at each side of the bristles 54 . this allows the bristles to flex and recover during operation . since this type of brush is capable of sealing positive or negative pressure changes with respect to the axial direction , it is a bi - directional brush . the use of such bi - directional brushes is preferred because it can simplify the manufacturing process and avoid a possible installation error . in the embodiment illustrated in fig4 a brush seal 52 is mounted in a t - shaped slot 60 defined in at least one and preferably each circumferential end of one of the seal ring segments 112 . as illustrated , the slot extends in a direction that is generally radially with respect to a center of the shaft ( not shown in fig4 ) disposed through the seal ring . in the illustrated embodiment , a seal slot 62 is machined in the circumferential end of the seal ring segment facing the brush to receive the same to provide an additional guarantee of oil sealing . under normal operating conditions , the two seal ring segments 112 , 114 contact each other so that no oil flows between them . however , in the event of sealing malfunction , the brush seal is brought into play to seal oil that would otherwise seep between the open seal ring segments . as illustrated , the brush seal 52 is preferably but is not necessarily mounted to each circumferential end of the upper seal ring segment 112 . the brush seals may be installed to the seal ring segment in any one of a number of ways . for example , with reference to fig5 a gap 64 can be reserved between the metal plate ( s ) 56 to which the brush 54 is mounted and the opposing wall ( s ) of the t - shaped slot or cut out in which the brush seal is disposed . a spring mechanism such as a leaf spring 66 can then be disposed between the brush seal and the wall of the slot of the seal ring to urge the brush seal toward the other seal ring segment . although in this embodiment one leaf spring is preferably disposed at the top of the brush seal , a leaf spring or other spring structure may be disposed in addition or in the alternative between opposed side wall ( s ) of the brush and groove . another alternate spring structure for mounting the brush seal is to provide a rubber strip 68 fit into a space at the side ( fig6 ) or top of the brush seal . more specifically , a rubber strip may be disposed in the t - shaped slot or against a surface of the brush seal in a stretched disposition to reduce its thickness . once the parts are assembled , the strip is released . when the strip is released , it will tend to recover its original thickness and will tighten or wedge the brush seal within the slot or groove of the seal ring . another alternative is shown in fig7 . in this embodiment , the ends of each brush seal may be spot welded as at 70 to reliably secure the brush seal 52 with respect to the seal ring 112 . it is apparent that spot welding would be the most reliable attachment of the brush seal to the spring ring segment . yet another mounting alternative , shown in fig8 is to fix the brush seal 52 to the seal ring segment 112 at the side of the seal brush with one or more screws or bolts 74 ( only one of which is shown in fig8 ). in this case , to avoid damaging the bristles , the screw or bolt hole ( s ) 76 in the metal plate ( s ) 56 should not go through the bristles . other known mechanical attachments , components and methods could be used to secure the brush seals with respect to seal rings , as will be appreciated by the skilled artisan . while in the illustrated embodiment , the brush seal is illustrated as mounted to each circumferential end of the upper seal ring , since it is desirable for the seal brush to depend downwardly , it is to be understood that the gap seal , such as a brush seal , could in the alternative be mounted to the lower seal ring for extending to and sealingly contacting a seal slot therefor . as a further alternative , each seal ring segment could be provided with a gap seal structure , such as a brush seal , at one circumferential end and a complementary structure , such as a groove , at the other circumferential end . in most brush seal applications , bristle wear is a problem that will affect the sealing operation . in the embodiments of the invention , since the brush does not contact any rotating surfaces , no such wear problem would be expected . while the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment , it is to be understood that the invention is not to be limited to the disclosed embodiments , but on the contrary , is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims .