Dual hydorstatic seal assembly

A seal assembly includes first and second rings. The first ring includes a first outer ring, a first beam connected to the first outer ring, and a first shoe. The first shoe includes free and fixed ends and is configured to move radially. The second seal ring is disposed axially adjacent and is attached to the first seal ring. The second seal ring includes a second outer ring, a second beam connected to the second outer ring, and a second shoe. The second shoe includes free and fixed ends and is configured to move in a generally radial direction. The free end of the second shoe is disposed axially adjacent to the fixed end of the first shoe. The fixed end of the second shoe is disposed axially adjacent to the free end of the first shoe.

BACKGROUND

The present disclosure relates generally to seal assemblies, and more particularly to seal rings for use in gas turbine engines.

Honeycomb and knife-edge seals can be used to form a seal at the interface between rotating and static components within the turbine section of a gas turbine engine. Over time, knife-edge seals can wear a trench into the honeycomb causing gaps and sporadic increased leaks over time.

Floating non-contact seal (a.k.a., hydrostatic seal) configurations allow radial motion of shoe components relative to a rotating component. Seal rings can vary a gap between the sealing element and a rotating component by adjusting in response to the change in pressure across the sealing element. A shoe component of the floating non-contact seal is drawn radially inward and outward (toward and away) from the rotating component in response to the pressure across the sealing element. The shoe is supported on one end by spring-like beams. The shoe has a distributed load that is acted over the shoe from flow of a fluid passing across the seal. Because of this, the shoe effectively deforms as a cantilevered beam creating clearance variation with the rotating component thereby reducing sealing effectiveness. The shoe is configured such that the free end of the shoe deflects further inboard and outboard than the fixed end of the shoe. Due to this, the sealing effectiveness of the shoe is limited and a propensity for clash with the rotating component is increased.

Structures and configurations of seal rings are the subject of the following commonly owned U.S. Patent Publications US2016/0130963A1, US2015/0322816A1, and US2015/0285152A1 (incorporated by reference herein in their entireties).

SUMMARY

A seal assembly includes first and second rings. The first ring includes a first outer ring, a first beam connected to the first outer ring, and a first shoe. The first shoe includes free and fixed ends and is configured to move radially. The second seal ring is disposed axially adjacent and is attached to the first seal ring. The second seal ring includes a second outer ring, a second beam connected to the second outer ring, and a second shoe. The second shoe includes free and fixed ends and is configured to move in a generally radial direction. The free end of the second shoe is disposed axially adjacent to the fixed end of the first shoe. The fixed end of the second shoe is disposed axially adjacent to the free end of the first shoe.

A seal assembly for use in a gas turbine engine that includes a rotating structure, a static structure aligned with the rotating structure along a radial direction, and a floating non-contact seal disposed between the rotating structure and the static structure. The floating non-contact seal includes a first seal ring, a second seal ring disposed axially adjacent and attached to the first seal ring, a pin, and a seal element. The first seal ring includes a first outer ring, a first beam connected to the first outer ring, and a first shoe connected to and extending from the first beam. The first shoe includes a first free end and a first fixed end. The second seal ring includes a second outer ring, a second beam connected to the second outer ring, and a second shoe connected to and extending from the second beam. The second shoe includes a second free end and a second fixed end. The second free end of the second shoe is disposed axially adjacent to the first fixed end of the first shoe. The second fixed end of the second shoe is disposed axially adjacent to the first free end of the first shoe. The pin is engaged with the first seal ring and the second seal ring such that the first and second seal rings are attached to each other via the pin. The seal element is connected to and extends radially inward from at least one of the first shoe and the second shoe.

A method includes drawing a fluid across a hydrostatic seal assembly that includes a first hydrostatic seal ring and a second hydrostatic seal ring disposed axially adjacent and attached to the first seal ring. The first hydrostatic seal ring includes a first outer ring, a first beam connected to the first outer ring, and a first shoe connected to and extending from the first beam. The first shoe includes a first free end and a first fixed end. The second hydrostatic seal ring includes a second outer ring, a second beam connected to the second outer ring, and a second shoe connected to and extending from the second beam. The second shoe includes a second free end and a second fixed end. The first free end and the first fixed end of the first shoe are moved in a radial direction in response to a pressure differential across the seal assembly. The second free end of the second shoe is moved by way of the second free end being attached to the first fixed end of the first shoe. The second fixed end of the second shoe is moved by way of the second fixed end being attached to the first free end of the first shoe.

DETAILED DESCRIPTION

FIGS. 1, 2, and 3show different aspects of seal assembly10with rotating structure12, static structure14, first seal ring16A, and second seal ring16B and are discussed as a group below.FIG. 1is a cross-section view of seal assembly10such that a downstream direction is left to right inFIG. 1.FIG. 2is a cross-sectional view of seal assembly10with rotating structure12, static structure14, and seal ring16B taken along2-2inFIG. 1.FIG. 3is a perspective view of seal assembly10with rotating structure12and static structure14omitted for clarity. Additionally, the views of seal assembly10inFIGS. 2 and 3represent a portion of an entire circumference of seal assembly10which extends in a complete annulus, circle, or ring. As discussed in U.S. Patent Publications US2016/0130963A1, US2015/0322816A1, and US2015/0285152A1, seal assembly10with first and second seal rings16A and16B can be located within the turbine section of a gas turbine engine.

Seal assembly10includes rotating structure12, static structure14, first seal ring16A, and second seal ring16B. First seal ring16A includes first outer ring18A (with first hole20A), first shoe22A (with first free end24A and first fixed end26A), and first beams28A. Second seal ring16B includes second outer ring18B (with second hole20B), second shoe22B (with second free end24B and second fixed end26B), and second beams28B. Seal assembly10further includes spacer30, carrier32, pin34, plate36, seal cover38, and seals40(with first seal40A and secondary seal40B). First shoe22A includes teeth42. A space between rotating structure12and teeth42forms gap44. First shoe22A includes upstream portion46and second shoe22B includes downstream portion48. Seal assembly10additionally includes upstream face50of seals40, downstream face52of seal cover38, downstream face54of seals40, and upstream face56of first shoe22A.FIGS. 2 and 3show seal assembly10additionally including stems58, arms60, and extensions62.

Rotating structure12includes a structure of a gas turbine engine that is rotating. In one non-limiting embodiment, rotating structure12can include a rotor of a compressor section or a turbine section of a gas turbine engine. Static structure14includes a structure of a gas turbine engine that is static or non-rotating. In one non-limiting embodiment, static structure14can include a stator of a compressor section or a turbine section of a gas turbine engine.

First and second seal rings16A and16B include hydrostatic fluid or floating non-contact seals. In one non-limiting embodiment, first and/or second seal rings16A and16B can be made out of a nickel alloy material, such as an austenitic nickel-based superalloy, or other metallic alloys favorable for use in high temperature applications. In some non-limiting embodiments, an axial thickness or width of either first seal ring16A or second seal ring16B can be 0.1 to 0.375 inches (0.254 to 0.95 centimeters). First and second outer rings18A and18B include rings of solid material. First and second holes20A and20B include narrow apertures or openings.

First and second shoes22A and22B include solid pieces of material with partially annular shapes and generally rectangular shaped cross-sections (from the viewpoint of looking into the page inFIG. 1). First shoe22A includes first free end24A, first fixed end26A, and upstream portion46. Second shoe22B includes second free end24B, second fixed end26B, and downstream portion48. First free end24A includes an end of first shoe22A that is not attached directly to first beam28A. Second free end24B includes an end of second shoe22B that is not directly attached to second beam28B. First end26A includes an end of first shoe22A that is attached directly to first beam28A on an opposite end of first beam28A that is attached directly to first outer ring18A. Second fixed end26B includes an end of second shoe that is attached directly to second beam28B on an opposite end of second beam28B that is attached directly to second outer ring18B.

First and second beams28A and28B include elongate resilient elements or springs capable of springing back into shape upon radial deflection (upward or downward inFIGS. 1 and 2). In one non-limiting embodiment, first beam28A and/or second beam28B can include two (as shown inFIGS. 1 and 2) or more individual beams. Spacer30(FIG. 1) includes a ring-shaped plate of solid material. Carrier32(FIG. 1) includes an annular ribbon or sleeve of solid material. Pin34(FIG. 1) includes a peg or dowel of solid material. In other non-limiting embodiments, pin34can be replaced with a braze or weld joint. In one non-limiting embodiment, seal assembly10can include first pin34A, second pin34B, and third pin34C (as shown inFIG. 3). In other non-limiting embodiments, seal assembly10can include more or less than three pins to affix portions of first seal ring16A to portions of second seal ring16B such as first free end24A to second fixed end26B, first fixed end26A to second free end24A, and first outer ring18A to second outer ring18B.

Plate36(FIG. 1) includes a ring-shaped plate of solid material. Plate36includes scallops or holes (not shown inFIG. 1) along plate36. Seal cover38(FIG. 1) includes a ring of solid material. Seals40(FIG. 1) include ring-shaped, or partially ring-shaped, pieces of pliant solid material, which can include a cobalt alloy or other types of metallic alloys suitable for wear resistance. Seals40extend in a vertical direction as shown inFIG. 1. In this non-limiting embodiment, seals40include two seals (e.g., first seal40A and secondary seal40B), but in other non-limiting embodiments can include more or less than two seals. Teeth42include solid pieces of material and ring-shaped are seal elements. Gap44(FIG. 1) includes a space between teeth42and rotating structure12.

Upstream portion46of first shoe22A includes a portion of first shoe22A that is located on an upstream (to the left inFIG. 1) end of first shoe22A. Downstream portion48of second shoe22B includes a portion of second shoe22B that is located on a downstream (to the right inFIG. 1) end of second shoe22B. Upstream face50includes a face of first seal40A that faces in an upstream direction and is located at an upstream end of seals40. Downstream face52includes a face of seal cover38that faces in a downstream direction and is located at a downstream end of seal cover38. Downstream face54includes a face of secondary seal40B that faces in a downstream direction and is located at a downstream end of seals40. Upstream face56includes a face of first shoe22A that faces in an upstream direction and is located on upstream portion46of first shoe22A.

As shown inFIGS. 2 and 3, first and second stems58A and58B include solid ribbon-shaped pieces of material that extend along an axial length of first and second shoes22A and22B, respectively. First and second arms60A and60B include lips formed of solid material that extend partially radially outward from first and second shoes22A and22B, respectively. First and second extensions62A and62B include T-shaped pieces of solid material.

Seal assembly10is configured to be disposed in a turbine section of a gas turbine engine (omitted inFIGS. 1 and 2for clarity). Rotating structure12is disposed radially within first and second seal rings16A and16B and static structure14. In other non-limiting embodiments, static structure14can be disposed radially within rotating structure12with first and second seal rings16A and16B disposed radially between rotating structure12and static structure14. Static structure14is radially aligned with the rotating structure12such that static structure14and rotating structure12are aligned in a direction extending radially outward from rotating structure12. In one non-limiting embodiment, first and second seal rings16A and16B are attached to static structure14such that rotating structure12rotates relative to static structure14and first and second seal rings16A and16B during operation of seal assembly10.

First and second seal rings16A and16B are disposed radially inward of and are integrally formed with first and second outer rings18A and18B, respectively. First seal ring16A is attached and disposed axially adjacent to second seal ring16B. First seal ring16A is attached to second seal ring16B via mechanical attachment with pins34. In another non-limiting embodiment, first seal ring16A is attached to second seal ring16B via chemical attachment such as by welding or brazing. Second seal ring16B is attached and disposed axially adjacent to first seal ring16A. First and second outer rings18A and18B are positioned radially between carrier32and first and second beams28A and28B, respectively. First hole20A is disposed in a downstream face of first annular base18A. Second hole20B is disposed in an upstream face of second annular base18B. First and second holes20A and20B extend axially into portions of first and second seal rings16A and16B, respectively.

First shoe22A is connected to and extends from first beam28A. First shoe22A is configured to move in a generally radial direction relative to first outer ring18A and relative to rotating structure12. Second shoe22B is connected to and extends from second beam28B. Second shoe22B is configured to move in a generally radial direction relative to second outer ring18B. First free end24A is disposed on an opposite end of first shoe22A from first fixed end26A. First free end24A of first shoe22A is disposed axially adjacent to and is axially aligned (i.e., aligned along an axial direction relative to seal assembly10) with second fixed end26B of second shoe22B. Second free end24B is disposed on an opposite end of second shoe from second fixed end26B. Second free end24B of second shoe is disposed axially adjacent to and is axially aligned (i.e., aligned along an axial direction relative to seal assembly10) with first fixed end26A of first shoe22A. First fixed end26A of first shoe22A is connected to first beams28A. Second fixed end26B of second shoe22B is connected to second beams28B.

In one non-limiting embodiment, first and second beams28A and28B extend in a direction orthogonal to the axial direction of seal assembly10. First beams28A are integrally formed with first shoe22A such that first shoe22A and first beams28A can be formed out of a single piece of continuous material, and likewise for second shoe22B and second beams28B. In another non-limiting embodiment, first beams28A can be integrally formed with first outer ring18A and/or second beams28B can be integrally formed with second outer ring18B. First and second beams28A and28B include a dual-beam design which causes first and second shoes22A and22B to move in a radial direction (up and down inFIG. 1). In other non-limiting embodiments, first and/or second beams28A and28B can include more or less than two beams.FIG. 3shows a portion of the entire circumferences of first and second seal rings16A and16B. In one non-limiting embodiment, the entire circumference of first and/or second seal rings16A and16B can include approximately fifty shoes and corresponding sets of beams.

Spacer30is disposed axially downstream of seal cover32and axially upstream of first outer ring18A and first beams28A. Spacer30is positioned between first seal ring16A and seals40to create axial spacing between first beams28A and seals40. Carrier32includes a support ring for securing first and second seal rings16A and16B to static structure14. Carrier32is positioned radially between static structure14and first and second seal rings16A and16B. In other non-limiting embodiments, carrier32can be a part of static structure14. First pin34A is disposed in hole20to attach first outer ring18A to second outer ring18B. Second pin34B affixes or attaches first fixed end26A of first shoe22A to second free end24B of second shoe22B. Third pin34C affixes or attaches second fixed end26B of second shoe to first free end24A of first shoe22A. Plate36is disposed along a downstream side of second beams28B and second shoe22B. The scallops or holes (not shown) of plate36allow for fluid communication across plate36. Seal cover38is disposed axially upstream of seals40.

Seals40are disposed axially upstream of first beams28A and come into contact with upstream face56first shoe22A. Seals40are disposed between seal cover38and first shoe22A such that upstream face50of seals40is out of contact with downstream face52of seal cover38and downstream face54of seals40is in contact with upstream face56of first shoe22A. Upstream face56of first shoe22A includes a face of first shoe22A that faces in an upstream direction (to the left inFIG. 1) and is located downstream of a furthest upstream portion of first shoe22A. Teeth42are connected to and extend radially inward from first shoe22A and into gap44. In another non-limiting embodiment, teeth42are connected to and extend radially inward from at least one of first shoe22A and second shoe22B. Gap44is formed between teeth42and rotating structure12for allowing air flow F to pass across first and second seal rings16A and16B in a downstream direction (as shown by the direction of the arrowheads of air flow F). InFIGS. 1 and 3, a direction of fluid flow is generally left to right.

First and second stems58A and58B are connected to and extend radially inward from first and second outer rings18A and18B, respectively. First and second arms60A and60B are attached to, or formed as a part of, first and second shoes22A and22B, respectively. First and second arms60A and60B form a notch with first and second shoes22A and22B, respectively creating a space for first and second extensions62A and62B, respectively to be disposed in. Spacing is provided between first and second extensions62A and62B and first and second arms60A and60B, respectively to allow first and second arms60A and60B to move as first and second shoes22A and22B move radially inward or outward. First and second extensions62A and62B are connected to first and second outer rings18A and18B, respectively by first and second stems58A and58B, respectively.

During operation of seal assembly10, first seal ring16A sealingly engages with rotating structure12to control an amount of fluid and fluid pressure across first seal ring16A between components of a gas turbine engine. Floating non-contact seal16adjusts in response to the change in pressure across first seal ring16A by drawing first shoe22A towards or away from rotating structure12to adjust gap44between first shoe22A and rotating structure12. As first shoe22A is drawn towards or away from rotating structure12, second shoe22B is also drawn towards or away from rotating structure12due to first shoe22A and second shoe22B being attached via pins second and third30B and30C.

During operation of seal assembly10, first and second seal rings16A and16B regulate air flow F from a high pressure side of first and second seal rings16A and16B (to the left inFIG. 1) to a low pressure side of first and second seal rings16A and16B (to the right inFIG. 1). As air flow F flows past teeth42of first seal ring16A, a pressure field across seal assembly10changes. First and second shoes22A and22B are drawn towards or away from rotating structure12due to a pressure differential across a radially inward side and a radially outward side of first and second shoes22A and22B. If the pressure differential across first and second shoes22A and22B are high, first and second shoes22A and22B are pushed by the high pressure in a radially outward direction to allow the high pressure flow to release into the area of low pressure through plate36. If the pressure differential across first and second shoes22A and22B are low, the radially outward force applied to first and second shoes22A and22B is lessened which lowers first and second shoes22A and22B radially inward towards rotating structure12restricting and thereby reducing the amount of flow F allowed past first and second shoes22A and22B.

First pin34A attaches or affixes first outer ring18A to second outer ring18B to prevent relative rotation between first and second seal rings16A and16B. Radially inward and outward motion of first and second shoes22A and22B is limited by the configuration of first and second stems58A and58B, first and second arms60A and60B, and first and second extensions62A and62B. As first and second shoes22A and22B move radially outward, first and second arms60A and60B come into contact with portions of first and second beams28A and28B, respectively which prevents a large clearance between first and second shoes22A and22B and rotating structure12from occurring. Conversely, as first and second shoes22A and22B moves radially inward, first and second arms60A and60B come into contact with first and second extensions62A and62B preventing teeth42of first shoe22A from coming into contact with rotating structure12.

As the pressure differential across floating non-contact seal16balances out, first and second shoes22A and22B move radially outward and inward (upward and downward inFIGS. 1 and 2) until pressure equilibrium is achieved, for example a pressure of upstream of first and second shoes22A and22B and a pressure downstream of first and second shoes22A and22B becomes equal. The pressure equilibrium across first and second shoes22A and22B results in a force balance allowing first and second shoes22A and22B to adjust the size of gap44and maintaining clearances between teeth42of first shoe22A and rotating structure12. As first and second shoes22A and22B move up and down, seals40slide along first shoe22A to maintain sealing engagement and force balances. First and second outer rings18A and18B function to support first and second seal rings16A and16B, respectively. First and second outer rings18A and18B extend for the entire circumference of first and second seal rings16A and16B, respectively.

In prior art seal assemblies with a single seal ring, each shoe deforms similar to a cantilevered beam. Since the shoe is supported on one end with a distributed load acted over the shoe from the flow across the seal, the free end of the shoe deflects further inboard and outboard than the fixed end. Put another way, existing shoes are cantilevered such that a first end of the shoe is lifted and lowered differently than the second end of the shoe causing a non-uniform sealing engagement with the rotating structure across a length of the shoe (i.e., the gap between the teeth and the rotating structure is non-uniform along the length of a particular shoe). This motion creates clearance variation across the shoe which reduces sealing effectiveness of the seal ring and causes an imbalance across the entire circumference of the rotating element. Propensity for the shoe to clash with the rotating element is also increased potentially causing wear, damage, and/or engine failure.

Seal assembly10addresses these issues by causing first and second shoes22A and22B to move up and down evenly. In other words, as first shoe22A is moved due to its hydrostatic sealing effect, first free end24A will have the same rate of radial motion as first fixed end26A by way of first shoe22A and second shoe22B being attached via second and third pins34B and34C. Likewise, second free end24B and second fixed end26B of second shoe22B will have the same amount of radial motion as second shoe22B is moved due to its hydrostatic sealing effect. Seal assembly10with first and second seal rings16A and16B minimizes the sealing ineffectiveness of the shoes by having motions of first shoe22A and second shoe22B complement each other to effectively eliminate the individual cantilevered motion of first and second shoes22A and22B. Second shoe22B reduces the cantilevered nature of first free end24A of first shoe22A by way of second fixed end26B being attached to first free end24A by third pin34C. Likewise, first shoe22A reduces the cantilevered nature of second free end24B of second shoe22B by way of first fixed end26A being attached to second free end24B of second shoe22B by second pin34B. The net effect of first and second shoes22A and22B balancing out the cantilevered effect of the other shoe is a more even sealing effect from each shoe as compared to single cantilevered shoes in existing designs.

The configuration of seal assembly10with first and second seal rings16A and16B also reduces the manufacturing burden of creating seal assembly10by reducing the axial thickness of first and second seal rings16A and16B as compared to a single seal ring. This reduction in thickness allows for the use of manufacturing processes, such as laser waterjet, etc., that are typically unsuitable for relatively thicker pieces of material. Here, first and second seal rings16A and16B are thin enough to allow use of a laser waterjet process without the occurrence of issues such as coning of the cutting channel or tapering of the part which occurs with thicker workpieces.

Discussion of Possible Embodiments

A seal assembly includes first and second rings. The first ring includes a first outer ring, a first beam connected to the first outer ring, and a first shoe. The first shoe includes free and fixed ends and is configured to move radially. The second seal ring is disposed axially adjacent and is attached to the first seal ring. The second seal ring includes a second outer ring, a second beam connected to the second outer ring, and a second shoe. The second shoe includes free and fixed ends and is configured to move in a generally radial direction. The free end of the second shoe is disposed axially adjacent to the fixed end of the first shoe. The fixed end of the second shoe is disposed axially adjacent to the free end of the first shoe.

The seal assembly can further comprise a hydrostatic seal.

The seal assembly can be configured to be disposed in a turbine section of a gas turbine engine.

The seal assembly can further comprise a spacer that can be disposed axially adjacent and/or in contact with one of the first seal ring or the second seal ring, a secondary seal that can be in contact with the spacer and/or against one of the first seal ring or the second seal ring, a seal cover that can be in contact with a portion of the spacer such that the seal cover can retain the secondary seal against the spacer and/or one of the first seal ring or the second seal ring, a carrier that can be disposed radially outward from the first seal ring and/or the second seal ring, and a seal plate that can be disposed on an axial end of the seal assembly opposite from the seal cover, wherein the seal plate can be radially inward from and/or in contact with the carrier.

The first seal ring can be attached to the second seal ring via mechanical attachment.

A pin can be engaged with the first seal ring and/or the second seal ring such that the first and second seal rings can be attached to each other via the pin.

The seal assembly can further comprise a plurality of pins, wherein a first pin of the plurality of pins can attach the first outer ring of the first seal ring to the second outer ring of the second seal ring, wherein a second pin of the plurality of pins can attach the first free end of the first shoe to the second fixed end of the second shoe, and wherein a third pin of the plurality of pins can attach the first fixed end of the first shoe to the second free end of the second shoe.

The first seal ring can be attached to the second seal ring via chemical attachment.

The first seal ring can be attached to the second seal ring by welding or brazing.

The first shoe of the first seal ring can be circumferentially aligned with the second shoe of the second seal ring.

A seal element can be connected to and/or extend radially inward from at least one of the first shoe and the second shoe.

A seal assembly for use in a gas turbine engine that includes a rotating structure, a static structure aligned with the rotating structure along a radial direction, and a floating non-contact seal disposed between the rotating structure and the static structure. The floating non-contact seal includes a first seal ring, a second seal ring disposed axially adjacent and attached to the first seal ring, a pin, and a seal element. The first seal ring includes a first outer ring, a first beam connected to the first outer ring, and a first shoe connected to and extending from the first beam. The first shoe includes a first free end and a first fixed end. The second seal ring includes a second outer ring, a second beam connected to the second outer ring, and a second shoe connected to and extending from the second beam. The second shoe includes a second free end and a second fixed end. The second free end of the second shoe is disposed axially adjacent to the first fixed end of the first shoe. The second fixed end of the second shoe is disposed axially adjacent to the first free end of the first shoe. The pin is engaged with the first seal ring and the second seal ring such that the first and second seal rings are attached to each other via the pin. The seal element is connected to and extends radially inward from at least one of the first shoe and the second shoe.

The seal assembly can be disposed in a turbine section of the gas turbine engine.

The floating non-contact seal can comprise a hydrostatic seal.

The floating non-contact seal can be configured to sealingly engage with the rotating element.

A method includes drawing a fluid across a hydrostatic seal assembly that includes a first hydrostatic seal ring and a second hydrostatic seal ring disposed axially adjacent and attached to the first seal ring. The first hydrostatic seal ring includes a first outer ring, a first beam connected to the first outer ring, and a first shoe connected to and extending from the first beam. The first shoe includes a first free end and a first fixed end. The second hydrostatic seal ring includes a second outer ring, a second beam connected to the second outer ring, and a second shoe connected to and extending from the second beam. The second shoe includes a second free end and a second fixed end. The first free end and the first fixed end of the first shoe are moved in a radial direction in response to a pressure differential across the seal assembly. The second free end of the second shoe is moved by way of the second free end being attached to the first fixed end of the first shoe. The second fixed end of the second shoe is moved by way of the second fixed end being attached to the first free end of the first shoe.

The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following steps, features, configurations and/or additional components.

Relative motion between the first seal ring and the second seal ring can be prevented with a first pin engaged with the first and/or second seal rings.

A second pin can be moved with the first fixed end of the first shoe, wherein the second pin can be engaged with the first fixed end of the first shoe and/or with the second free end of the second shoe such that as the first fixed end moves the second pin, the second pin can cause the second free end of the second shoe to move.

A third pin can be moved with the first free end of the first shoe, wherein the third pin can be engaged with the first free end of the first shoe and/or with the second fixed end of the second shoe such that as the first free end moves the third pin, the third pin can cause the second fixed end of the second shoe to move.

A uniform gap can be maintained between the first free end and the first fixed end relative to the rotating structure as the first shoe is moved radially.