Abstract:
A seal ring assembly includes a first seal ring axially disposed from a second seal ring. The first seal ring has an axial face opposing an axial face of the second seal ring. A radial oil channel is defined between the two axial faces. Both seal rings have a tapered surface configured to contact a spring. The spring biases the seal rings away from each other via the tapered surface. Both seal rings are disposed in a radially inwardly directed channel. At least one of the seal rings have a plurality of protrusions that extend beyond the axial face. The protrusions are configured to create a passageway to allow oil to flow through the passageway and to allow at least one of the seal rings to move into a desired position by reducing static friction between the axial faces.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to hydrogen seal rings and, more specifically, to a seal structure for automatically resetting in the event of oil pressure loss and subsequent restoration, by reducing oil leakage through a circumferential gap between the seal ring segments and seal structure in a hydrogen cooled generator. 
         [0002]    Hydrogen has been widely used as a coolant in a variety of rotary dynamoelectric machines, due to its desirable thermophysical properties including low density and high specific heat. However, a primary disadvantage of using hydrogen is that the hydrogen purity must be maintained above its explosive limit (74% hydrogen in air). Therefore, a primary consideration for ensuring the safe operation of hydrogen-cooled rotary machines, such as turbo-generators, is designing highly reliable and efficient hydrogen seal systems therefor. 
         [0003]    In a hydrogen-cooled generator, hydrogen seals are utilized both to seal high-pressure hydrogen at the interface of the rotating shaft, and to prevent air from entering the casing and developing an explosive mixture with the hydrogen. Before the early  1980 s, hydrogen seal systems consisted of a pair of four segmented bronze rings disposed in a seal casing. The newer babbitted steel seal rings  10  are each made in two 180° segments  12 ,  14  as illustrated in  FIG. 1 . A typical hydrogen seal system is schematically shown in  FIG. 2 . In that illustration, an annular seal casing is partially shown which is adapted to be mounted to a generator end shield (not shown) in surrounding and sealing relationship with a rotor/shaft  16 . The casing is formed in two main parts, referred to hereinbelow as casing halves, each extending 180° about the shaft. For ease of description, the upper casing half  18  and the seal ring segments  12  disposed therein are illustrated and will be described in detail. It is to be understood, however, in an exemplary embodiment, the lower casing half has a corresponding construction. The upper casing half  18  is of two-part construction, including a seal casing main body  20  and a seal casing cap segment  22 . The seal casing cap segment has a generally h-shaped cross-section, forming a radially inwardly directed chamber  24  opening in a radially inward direction towards the shaft  16  for housing radially inwardly projecting seal rings  12  which in turn engage the shaft. 
         [0004]    Each seal casing cap segment  22  is formed with an axial portion  26  connecting an upper radial flange portion  28  and lower inner radial portion  30  and outer radial portion  32 . The axial portion  26  thus defines a base for the chamber  24  while radial portions  30  and  32  form two, axially spaced, parallel sides of the chamber  24 . Axially opposed shoulders  34 ,  36  define an opening facing the rotor shaft  16 . The seal casing cap segment  22  is fastenable to the seal casing main body  20  by a semi-annular array of bolts  38  passing through holes in the radial flange portion  28  of the cap and threadably received in the main body  20 . 
         [0005]    Within the chamber  24 , there are seated a pair of side-by-side seal ring segments  12 , each extending approximately 180° about the casing half  18 . The rings  10  are held together radially and apart axially by two coil springs  40  (only one of which is shown in  FIG. 2 ), each extending substantially 180° within the chamber  24 . The spring is seated within an area created by tapered surfaces  42  on the respective ring segments  12 . Opposite ends of the spring are anchored to axially extending pins (not shown) via a hook or the like (not shown) formed at each end thereof. As is conventional, the pin is located within aligned bores in radial wall portions of the casing cap segment. The pin is also used to align and hold a labyrinth type oil seal  46 . The spring biases the seal ring segments  12  radially inwardly and in axially opposite directions, against opposed faces of the inner and outer radial wall portions  30 ,  32  of the chamber  24 . 
         [0006]    In use, seal oil is introduced into the cavity of chamber  24  behind or radially outside the seal rings  12 , at a pressure higher than the hydrogen pressure inside the casing. Then, the high pressure seal oil flows radially between the seal rings  12  toward the rotating shaft  16 , where the sealing oil flow divides and runs axially with the clearance between the shaft and seal rings. At the hydrogen side  48  of the seal rings, the oil flows evenly between the shaft and the inner seal ring all the way around the seal ring at their interface and thus seals hydrogen from leaking and keeps the seal ring centered on the shaft. Similarly, the oil is uniformly distributed between the shaft  16  and the outer seal ring at the air side  50  of the seal. 
         [0007]    As illustrated in  FIG. 1 , hydrogen seal rings  10  are usually made into segments  12 ,  14 , split at horizontal joints. The two segments can either be bolted together at the horizontal joint or held by two coil springs suitably attached to the casing. As noted above, the purpose of the hydrogen seal springs  40  is to separate the two sealing rings and keep the sides of the rings against the casing. In normal operation, these rings maintain a uniform clearance and do not allow oil leakage at the ring segment joints. They are free to expand radially but prevented from rotating by either the pins to which the springs are attached or an anti-rotation device. In this way, the rings can float freely with respect to the seal casing cap  22 . 
         [0008]    However, under certain circumstances, the seal rings  12  may stick together so that oil ceases to flow between the seal rings. One possible cause is a loss in seal oil pressure. If the seal oil pressure drops to an undesirably low level the inner seal oil ring may move towards the outer seal ring until their axial surfaces make contact. This blocks the oil flow channel and the seal rings can be resistant to separating due to static friction between the two axial surfaces. Another problem is that when both seal rings contact each other in this manner, a large channel is opened up between the shoulder  34  and the opposing surface of the seal ring  12 . This channel can allow oil to flow into the generator in undesirable quantities and possibly result in a forced shutdown of the generator. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0009]    In an aspect of the present invention, a seal ring assembly includes a seal casing defining a radially inwardly directed channel. A first seal ring is axially disposed from a second seal ring. The first seal ring has a first axial face opposing a second axial face of the second seal ring. A radial oil channel is defined between the first axial face and the second axial face. Both the first seal ring and the second seal ring have a tapered surface configured to contact a spring, and this is spring configured to bias the first seal ring away from the second seal ring via the tapered surface. The first seal ring and the second seal ring are disposed in the radially inwardly directed channel. At least one of the first seal ring or the second seal ring have a plurality of protrusions that extend beyond the first axial face or the second axial face. The plurality of protrusions are configured to create a passageway to allow oil to flow through the passageway and to allow at least one of the first seal ring or the second seal ring to move into a desired position by reducing static friction between the first axial face and the second axial face. 
         [0010]    In another aspect of the present invention, a seal ring assembly includes a seal casing defining a radially inwardly directed channel, and a first seal ring axially disposed from a second seal ring. The first seal ring has a first axial face opposing a second axial face of the second seal ring. A radial oil channel is defined between the first axial face and the second axial face. Both the first seal ring and the second seal ring have a tapered surface configured to contact a spring, and the spring is configured to bias the first seal ring away from the second seal ring via the tapered surface. The first seal ring and the second seal ring are disposed in the radially inwardly directed channel. At least one of the first seal ring or the second seal ring have a plurality of protrusions that extend beyond the first axial face or the second axial face. The plurality of protrusions are configured to create a passageway to allow oil to flow through the passageway and to allow at least one of the first seal ring or the second seal ring to move into a desired position by reducing static friction between the first axial face and the second axial face. The plurality of protrusions extend about one third to about one half of the way into the radial oil channel. Both the first seal ring and the second seal ring comprise a wearable material located at an inner radial position thereof, and the wearable material is configured to reduce wear on a rotor shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  illustrates a perspective view of one known seal ring. 
           [0012]      FIG. 2  illustrates a partial, cross-sectional view of a known seal assembly. 
           [0013]      FIG. 3  illustrates a sequence of events that lead to oil ingress into the hydrogen cooled generator. 
           [0014]      FIG. 4  illustrates a seal ring assembly, according to an aspect of the present invention. 
           [0015]      FIG. 5  illustrates and axial end view of the hydrogen side seal ring as shown in  FIG. 4 , according to an aspect of the present invention. 
           [0016]      FIG. 6  illustrates a seal ring assembly, according to an aspect of the present invention. 
           [0017]      FIG. 7  illustrates an axial end view of the air side seal ring as shown in  FIG. 6 , according to an aspect of the present invention. 
           [0018]      FIG. 8  illustrates an axial end view of both the hydrogen side seal ring and the air side seal ring, according to an aspect of the present invention. 
           [0019]      FIG. 9  illustrates a side view of a single protrusion, according to an aspect of the present invention. 
           [0020]      FIG. 10  illustrates a front view of the protrusion as shown in  FIG. 9 . 
           [0021]      FIG. 11  illustrates a front view of a single protrusion, according to an aspect of the present invention. 
           [0022]      FIG. 12  illustrates a side view of a single protrusion, according to an aspect of the present invention. 
           [0023]      FIG. 13  illustrates a front view of the protrusion as shown in  FIG. 12 . 
           [0024]      FIG. 14  illustrates a partial view of a seal assembly, according to an aspect of the present invention. 
           [0025]      FIG. 15  illustrates a partial view of a seal assembly, according to an aspect of the present invention. 
           [0026]      FIG. 16  illustrates a partial view of a seal assembly, according to an aspect of the present invention. 
           [0027]      FIG. 17  illustrates a partial perspective view of a seal ring and a protrusion, according to an aspect of the present invention. 
           [0028]      FIG. 18  illustrates a cross-sectional view of the seal ring and the protrusion as shown in  FIG. 17 , according to an aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    One or more specific aspects/embodiments of the present invention will be described below. In an effort to provide a concise description of these aspects/embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with machine-related and system-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0030]    When introducing elements of various embodiments of the present invention, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters and/or environmental conditions are not exclusive of other parameters/conditions of the disclosed embodiments. Additionally, it should be understood that references to “one embodiment”, “one aspect” or “an embodiment” or “an aspect” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments or aspects that also incorporate the recited features. 
         [0031]      FIG. 3  illustrates a sequence of events that lead to oil ingress into the hydrogen cooled generator. The upper left portion of  FIG. 3  shows the seal assembly in its normal and desired operating state. The seal casing  322  has a chamber  324  that is filled with oil  301 , and this oil passes through the spring  340  and into the radial oil channel  305  (i.e., between axial faces  313 ,  314  of the seal rings). The oil  301  then travels between the rotor shaft  316  and the seal rings  312 H and  312 A. The seal ring  312 H is on the hydrogen side  348  of the seal assembly, and the seal ring  312 A is on the air side  350  of the seal assembly. For example, the hydrogen side  348  is internal to the hydrogen cooled generator and is under a higher pressure compared to the external air side  350 . 
         [0032]    It is possible to experience a loss of oil pressure and the upper right portion of  FIG. 3  illustrates this occurrence. The loss of oil pressure results in a net loss of force on the two seal rings  312 H,  312 A, and because of this the two seal rings contact each other along their axial faces  313 ,  314 . In the normal operating mode previously described, the oil passing between axial faces  313 ,  314  acts on and helps to keep the axial faces away from each other. In an oil pressure loss event, this repulsing force is lost and the force of the spring is not enough to maintain separation of the axial faces  313 ,  314 . The greater pressure of the hydrogen gas inside the generator overcomes the spring  340  and forces the hydrogen side seal ring  312 H over until axial face  313  contacts axial face  314 . The radial oil channel  305  now ceases to exist. In addition, hydrogen gas also flows into chamber  324  as well as externally to air side  350 . When the two axial faces  313 ,  314  contact each other they become difficult to separate due to the forces of static friction (or stiction). The force of the spring  340  is insufficient to move the seal rings  312 H and/or  312 A back into the desired position. 
         [0033]    The bottom center portion of  FIG. 3  illustrates when seal oil pressure is restored. As the seal oil pressure is restored oil  301  refills chamber  324 , but the radial oil channel  305  is completely blocked due to the two tightly bound axial faces  313 ,  314 . In this instance the oil  301  flows through the relatively large gap between the seal ring  312 H and the shoulder  334  of the seal casing  322 . This results in a large amount of oil flooding the generator and subsequently into a forced/automatic shutdown. The problem encountered here is that the seal rings  312 H,  312 A cannot automatically reset to their desired positions during an oil pressure loss and subsequent oil pressure restoration event. 
         [0034]      FIG. 4  illustrates a seal ring assembly  400 , according to an aspect of the present invention. The seal ring assembly includes a seal casing  422  having a chamber  424  that contains oil under pressure. The oil (not shown for clarity) flows through a spring  440  and a radial oil channel  405 . The radial oil channel  405  is defined by the space between an axial face  413  of a hydrogen side seal ring  412 H and the axial face  414  of the air side seal ring  412 A. Each of the seal rings  412 H and  412 A include a tapered surface  416 ,  417  configured to contact spring  440 . The tapered surfaces  417 ,  418  in conjunction with spring  440  impart both axial and radial forces on the seal rings  412 H,  412 A. Wearable materials  415  are located on the radially inward portion of both seal rings and are made of a relatively softer material than the seal rings to reduce damage to rotor shaft  416 . For example, wearable material  415  may be made of babbitt alloy, bronze or any other suitable material. The hydrogen side  448  of the seal is located on the left and the air side  450  is located on the right of  FIG. 4 . 
         [0035]    The seal ring  412 H includes a plurality of protrusions  460  that extend beyond the axial face  413 . For example, about six protrusions  460  may be distributed circumferentially about the axial face  413  so that each protrusion is spaced about 60 degrees away from a neighboring protrusion. In this example, the protrusions  460  are configured to extend about one third to about one half of the way into channel  405 . In the event of an oil pressure loss and movement of axial face  413  towards axial face  414 , this will allow for a satisfactory channel  405  to still exist between the two axial faces  413 ,  414 . As one specific example, the axial length of the radial oil channel  405  may be about 0.125 inches, and the axial length of the protrusions may be about 0.04 inches to about 0.06 inches. Even when the protrusions contact axial face  414 , channel  405  will still have an axial length of about 0.06 to 0.08 inches. These dimensions are only one example, and it is to be understood that any suitable combination of dimensions may be employed. The axial length of the protrusions may be less than one third of the channel length or more than half of the channel length. For example, the length of the protrusion may span up to the axial length of the channel less a small amount for axial thermal expansion allowance. This distance will be more than adequate to maintain oil flow along the channel  405  in the normal operating mode, and quickly restore separating oil pressure and flow to the axial faces  413 ,  414  of the seal rings, as well as greatly minimizing or reducing any problems due to static friction (stiction), following an oil pressure loss event. The circumferential width of the protrusions may be about 0.25 inches, while the radial length may be about 0.75 inches. This results in a very small surface area comprising the axial face  461  of the protrusions when compared to the surface area of the axial face  414  of the seal ring  412 A. In fact, the resulting static friction forces are so small that the combination of the spring  440  and oil flow through channel  405  are more than adequate to return the seal rings  412 H,  412 A back to their normal operating positions without having undesired oil leaks into the inside of the hydrogen cooled generator. 
         [0036]      FIG. 5  illustrates and axial end view of the hydrogen side seal ring  412 H as shown in  FIG. 4 , according to an aspect of the present invention. The seal ring  412 H is comprised of two halves, an upper half and a lower half. The upper half includes protrusions  460 A,  460 B and  460 C, each of which are spaced about 60 degrees from a neighboring protrusion. The lower half of the seal ring includes protrusions  460 D,  460 E and  460 F, each of which are spaced about 60 degrees from a neighboring protrusion. In this example, six protrusions are generally equally spaced around the axial face  413  of the seal ring  412 H. However, it is to be understood that more or less than six protrusions  460  may be employed. It will be apparent that the surface area of the axial faces  461  of the protrusions  460  are very small when compared to the surface area of axial faces  413  and  414 . This “reduced footprint” greatly reduces static friction between the two seal rings  412 H,  412 A and enables the seal rings to automatically reset in an oil pressure loss/restoration scenario. 
         [0037]      FIG. 6  illustrates a seal ring assembly, according to an aspect of the present invention. The protrusions  660  are located on the air side seal ring  612 A. The seal ring assembly includes a seal casing  622  having a chamber  624  that contains oil under pressure. The oil flows around and through a spring  640  and a radial oil channel  605 . The radial oil channel  605  is defined by the space between an axial face  613  of a hydrogen side seal ring  612 H and the axial face  614  of the air side seal ring  612 A. Each of the seal rings  612 H and  612 A include a tapered surface  616 ,  617  configured to contact spring  640 . Wearable materials  615  are located on the radially inward portion of both seal rings and are made of a relatively softer material than the seal rings to reduce damage to rotor shaft  616 . The hydrogen side  648  of the seal is located on the left and the air side  650  is located on the right of  FIG. 6 . 
         [0038]      FIG. 7  illustrates an axial end view of the air side seal ring  612 A as shown in  FIG. 6 , according to an aspect of the present invention. The seal ring  612 A is comprised of two halves, an upper half and a lower half. The upper half includes protrusions  660 A,  660 B and  660 C, each of which are spaced about 60 degrees from a neighboring protrusion. The lower half of the seal ring includes protrusions  660 D,  660 E and  660 F, each of which are spaced about 60 degrees from a neighboring protrusion. In this example, six protrusions are generally equally spaced around the axial face  614  of the seal ring  612 A. However, it is to be understood that more or less than six protrusions may be employed. 
         [0039]      FIG. 8  illustrates an axial end view of both hydrogen side seal ring  812 H and air side seal ring  812 A, according to an aspect of the present invention. The hydrogen side seal ring  812 H includes protrusions  860 A,  860 B and  860 C, each of which are spaced about 120 degrees from a neighboring protrusion on the same seal ring. The air side seal ring  812 A includes protrusions  860 D,  860 E and  860 F, each of which are spaced about 120 degrees from a neighboring protrusion. In this example, three protrusions are generally equally spaced around the axial face  813  of the seal ring  812 H and the axial face  814  of seal ring  812 A. The protrusions on the hydrogen side seal ring  812 H are offset from the protrusions on the air side seal ring  812 A. As other examples, each ring could have 2 protrusions spaced 180 degrees apart, or 4 protrusions spaced 90 degrees apart. However, it is to be understood that more or less than six protrusions may be employed, as desired in the specific application. When arranged side by side so that the two axial faces  813  and  814  face each other, the protrusions are spaced about 60 degrees away from each other. 
         [0040]      FIG. 9  illustrates a side view of a single protrusion  960 , according to an aspect of the present invention. The protrusion  960  may be integrally formed with the seal ring or attached to the seal ring. The protrusion includes two ramped surfaces  962 ,  964  located near the beginning and the end of the radial oil channel. Ramped surface  962  is located at a radially outward location and ramped surface  964  is located at a radially inward location. The ramped surfaces facilitate oil flow past the protrusions during normal operation (i.e., no oil pressure loss event). An axial face  966  of the protrusion has a reduced surface area due to the existence of the ramped surfaces  962 ,  964 . 
         [0041]      FIG. 10  illustrates a front view of the protrusion  960  shown in  FIG. 9 . This view is rotated 90 degrees with respect to  FIG. 9 . As shown, the protrusion  960  has a generally rectangular footprint. The axial face  966  that may contact the opposing axial face of the other seal ring has a reduced contact/surface area due to the ramped surfaces  962 ,  964 . 
         [0042]      FIG. 11  illustrates a front view of a single protrusion  1160 , according to an aspect of the present invention. The protrusion  1160  has a generally oval footprint for further oil flow enhancement. The protrusion  1160  includes two ramped surfaces  1162 ,  1164  located near the beginning and the end of the radial oil channel. Ramped surface  1162  is located at a radially outward location and ramped surface  1164  is located at a radially inward location. The ramped and tapered surfaces facilitate the flow of oil past the protrusions during normal operation (i.e., no oil pressure loss event). The axial face  1166  of the protrusion has a further reduced surface area due to the oval shape of the protrusion. 
         [0043]      FIG. 12  illustrates a side view of a single protrusion  1260 , according to an aspect of the present invention.  FIG. 13  illustrates a front view (rotated 90 degrees with respect to  FIG. 12 ) of the protrusion  1260 . The protrusion  1260  includes two ramped surfaces  1262 ,  1264  located near the beginning and the end of the radial oil channel. Ramped surface  1262  is located at a radially outward location and ramped surface  1264  is located at a radially inward location. The axial face  1266  of the protrusion includes a plurality of corrugations (or ribs)  1267 , and these further reduce the surface area of the axial face  1266 . It is to be understood that the pattern of the corrugations (or ribs) could have different orientations (e.g., angled by 30 degrees, 45 degrees, etc.), or the axial face  1266  could have a dimpled surface, a surface with multiple protrusions (e.g., hemispherical protrusions), or elements of any shape that decrease static friction between the seal rings and/or increase turbulation of oil passing through the radial oil channel. 
         [0044]      FIG. 14  illustrates a partial view of a seal assembly  1400 , according to an aspect of the present invention. The seal casing  1422  has a chamber  1424  that is filled with oil  1401 , and this oil passes through the spring  1440  and into the radial oil channel  1405  (i.e., between axial faces  1413 ,  1414  of the seal rings). The oil  1401  then travels between the rotor shaft  1416  and the seal rings  1412 H and  1412 A. The seal ring  1412 H is on the hydrogen side  1448  of the seal assembly, and the seal ring  1412 A is on the air side  1450  of the seal assembly. A plurality of seal ring springs  1470  may be provided on one or both of the seal rings  1412 H, A. The seal ring spring  1470  is configured to exert a force to push the axial face  1413  away from the axial face  1414 , and when fully compressed, will retain an axial gap in the flow channel  1405  of sufficient length to allow oil flow restoration following an oil pressure loss event. The spring  1470  may be comprised of a coil spring, a leaf spring or any other suitable spring. Similar to the protrusions previously described, the springs  1470  may be distributed about the seal ring(s) in a generally equal circumferential spacing. 
         [0045]      FIG. 15  illustrates a partial view of a seal assembly  1500 , according to an aspect of the present invention. The seal casing  1522  has a chamber  1524  that is filled with oil  1501 , and this oil passes through the spring  1540  and into the radial oil channel  1505  (i.e., between axial faces  1513 ,  1514  of the seal rings). The oil  1501  then travels between the rotor shaft  1516  and the seal rings  1512 H and  1512 A. The seal ring  1512 H is on the hydrogen side  1548  of the seal assembly, and the seal ring  1512 A is on the air side  1550  of the seal assembly. A distance separator  1570  extends radially inward from the seal casing  1522  into the radial oil channel  1505 . The distance separator  1570  prevents the two axial faces  1513 ,  1514  from contacting each other. The distance separator  1570  may be comprised of stainless steel, metal alloys or any other suitable material. Similar to the protrusions previously described, the distance separators  1570  may be distributed about the casing  1522  and between the seal ring(s) in a generally equal circumferential spacing. 
         [0046]      FIG. 16  illustrates a partial view of a seal assembly  1600 , according to an aspect of the present invention. The seal casing  1622  has a chamber  1624  that is filled with oil  1601 , and this oil passes through the spring  1640  and into the radial oil channel  1605  (i.e., between axial faces  1613 ,  1614  of the seal rings). The oil  1601  then travels between the rotor shaft  1616  and the seal rings  1612 H and  1612 A. The seal ring  1612 H is on the hydrogen side  1648  of the seal assembly, and the seal ring  1612 A is on the air side  1650  of the seal assembly. A distance separator  1670  extends radially inward from the spring  1640  into the radial oil channel  1605 , and may be integrally formed with the spring  1640  or attached thereto in any suitable manner (e.g., welding, mechanical fasteners, adhesives, etc.). The distance separator  1670  prevents the two axial faces  1613 ,  1614  from contacting each other. The distance separator  1670  may be comprised of stainless steel, metal alloys or any other suitable material. Similar to the protrusions previously described, the distance separators  1670  may be distributed around the spring  1640  and between the seal ring(s) in a generally equal circumferential spacing. 
         [0047]      FIG. 17  illustrates a partial perspective view of a seal ring  1712  and a protrusion  1760 .  FIG. 18  illustrates a cross-sectional view of the seal ring  1712  and the protrusion  1760 . The seal ring  1712  may include a plurality of cylindrical protrusions  1760  (i.e., having a substantially circular cross-sectional shape). The protrusions  1760  may be inserted or attached to the axial face  1713  by drilling a hole  1870  into the axial face  1713  of the seal ring  1712 . The protrusion  1760  can be inserted into the hole  1870  and held in place by an interference fit, adhesive, welding or any other suitable fastening system or process. As an additional example, the hole  1870  may be internally threaded and a portion of the protrusion  1760  can be externally threaded, and in this manner the protrusion can be screwed into and retained by the hole  1870 . The protrusion  1760  could be formed by any suitable shape, including but not limited to cross-sections that are rectangular, triangular, polygonal, circular or oval. An advantage to the circular/cylindrical protrusions  1760  is that they present a small to operationally insignificant obstruction to oil flowing through the radial channel, and they have a minimal axial area thereby reducing static friction (stiction) between the axial faces of the seal rings. 
         [0048]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.