Patent Description:
A turbine engine typically includes a housing that defines compartments therein and a rotatable shaft with or without a runner that passes through the compartments. Adjoining compartments typically separate one fluid from another fluid. In one example, one compartment may include a gas, such as combustion byproducts, and another may include a liquid, such as a lubricant. Mixture between the liquid and the gas within one compartment could compromise the integrity of the sealing assembly thereby adversely effecting performance and function of a gas turbine. As such, adjoining compartments must be isolated from one another by means of a sealing system that prevents one fluid, either a liquid or a gas, from migrating along a rotatable surface and entering a compartment so as to mix with another fluid therein. A circumferential seal is often implemented to avoid mixing between fluids and the problems caused thereby.

Referring now to <FIG>, a seal structure described by<CIT> is generally illustrated wherein a circumferential seal <NUM> is shown in contact with a garter spring <NUM> and a coil spring <NUM>. The garter spring <NUM> is typically disposed within a groove <NUM> about the circumference of the circumferential seal <NUM>. The coil spring <NUM> may be disposed within an optional pocket <NUM> at one side of the circumferential seal <NUM>. A typical circumferential seal <NUM> is composed of two or more ring segments with coil springs <NUM> and pockets <NUM> along each segment. The circumferential seal <NUM> is situated between a higher pressure side <NUM> at a higher pressure P<NUM> and a lower pressure side <NUM> at a lower pressure P<NUM>. The garter spring <NUM> urges the circumferential seal <NUM> in the direction of a radial sealing surface <NUM>. The radial sealing surface <NUM> may be disposed along the outer circumference of a shaft or a component attached to a shaft, one non-limiting example of the latter being a runner. The coil spring <NUM> urges the circumferential seal <NUM> in the direction of a forward sealing surface <NUM> disposed along the interior of a housing (not shown) adjacent to the circumferential seal <NUM>.

A forward face <NUM> of the circumferential seal <NUM> may sealingly engage the forward sealing surface <NUM> via cooperation between a radial bleed groove <NUM>, a face groove <NUM>, and a face dam <NUM>. A forward pressure <NUM> is communicated across the forward face <NUM> via a fluid contacting the circumferential seal <NUM>. The forward pressure <NUM> imparts a forward face force FF in the direction of the higher pressure side <NUM>.

An aft pressure <NUM> is communicated across an aft face <NUM> via a fluid contacting the circumferential seal <NUM>. The aft pressure <NUM> imparts an aft face force FA in the direction of the lower pressure side <NUM>. The coil spring <NUM> also imparts a spring force FS directed toward the lower pressure side <NUM>.

The total of the aft face force FA and the spring force FS is greater than or equal to the forward face force FF so that the forward face <NUM> contacts and sealingly engages the forward sealing surface <NUM>. In preferred embodiments, the force differential should be minimized to permit inward and outward movement of ring segments so that the circumferential seal <NUM> contracts and expands as required by conditions within a turbine engine.

An inward pressure <NUM> is communicated across an outer circumferential surface <NUM> via a fluid contacting the circumferential seal <NUM>. The inward pressure <NUM> imparts an inward radial force FI in the direction of the radial sealing surface <NUM>. The garter spring <NUM> also imparts a spring force FG directed toward the radial sealing surface <NUM>.

An inner circumferential surface <NUM> of the circumferential seal <NUM> may sealingly engage the radial sealing surface <NUM> via cooperation between a seal dam <NUM>, a bore groove <NUM>, and an axial bleed groove <NUM>. The seal dam <NUM> is biased toward the lower pressure side <NUM>. An outward pressure <NUM> is communicated across the inner circumferential surface <NUM> via a fluid contacting the circumferential seal <NUM>. The outward pressure <NUM> imparts an outward radial force FO in the direction away from the radial sealing surface <NUM>.

The total of the inward radial force FI and the spring force FG should be greater than or equal to the outward radial force FO so that the inner circumferential surface <NUM> sealingly engages the radial sealing surface <NUM>, preferably via a thin film <NUM>. In other preferred embodiments, the force differential should be minimized to permit inward and outward movement of ring segments so that the circumferential seal <NUM> contracts and expands as required by conditions within a turbine engine.

Performance and efficiency enhancements to turbine engines often require higher pressures and temperatures within the higher pressure side <NUM> and higher rotational speeds by the shaft and the radial sealing surface <NUM> thereon. High pressure and temperatures are problematic in that it is more challenging to properly balance the forward face force FF with respect to both the aft face force FA and the spring force FS and both the inward radial force FI and the spring force FG with respect to the outward radial force FO over a wider range of operating conditions.

For example, a circumferential seal <NUM> optimized for pressures and temperatures during flight may allow the aft face force FA to greatly exceed the forward face force FF and/or the inward radial force FI to greatly exceed the outward radial force FO when engine conditions require higher shaft speeds and pressures, such as at takeoff. The resulting imbalance effectively pins the circumferential seal <NUM> onto and against the face sealing surface <NUM> and the radial sealing surface <NUM> causing excessive wear to and heating of the circumferential seal <NUM>.

Wear and heating are further problematic in turbine engines that derive greater performance and higher efficiency via higher shaft speeds. At extreme conditions, a circumferential seal <NUM> may permit hot gases from the higher pressure side <NUM> to freely flow into the lower pressure side <NUM> so as to mix with and to cook oil lubricants therein. The end results could include an engine fire and/or flow conditions in the direction of the sump that blow lubricating oil away from the seal and the sealing surface.

<CIT> describes an intershaft sealing assembly for large diameter applications wherein a segmented seal ring is disposed between an inner shaft and an outer shaft. The wear and heating challenges discussed above are even more acute in large diameter applications.

Accordingly, what is required is a circumferential seal assembly interposed between a pair of compartments that minimizes leakage across a face sealing surface and a radial sealing surface within a turbine engine operating at higher shaft speeds and pressures.

Accordingly, what is also required is a circumferential seal assembly that reduces seating forces along a face sealing surface and a radial sealing surface within a turbine engine operating at higher shaft speeds and pressures.

An object of the invention is to provide a circumferential seal assembly interposed between a pair of compartments that minimizes leakage across a face sealing surface and a radial sealing surface within a turbine engine operating at higher shaft speeds and pressures.

Another object of the invention is to provide a circumferential seal assembly that reduces seating forces along a face sealing surface and a radial sealing surface within a turbine engine operating at higher shaft speeds and pressures.

In accordance with embodiments of the invention, the circumferential seal assembly includes a primary sealing ring, a ring-shaped insert, a second sealing ring, and a third sealing ring. The primary sealing ring is disposed within a housing along a rotatable element. The primary sealing ring sealingly engages both a face sealing surface of the housing and a radial sealing surface of the rotatable element. The primary sealing ring includes at least two seal segments. The ring-shaped insert is secured within the housing and/or is integral with the housing. A portion of the ring-shaped insert forms an outward flange which extends toward but does not contact the primary sealing ring. The second sealing ring is positioned within the primary sealing ring. The second sealing ring sealingly engages a portion of a face of the outward flange. The second sealing ring extends past the end of the outward flange so as to contact the inner circumferential surface of the primary sealing ring. The third sealing ring contacts and sealingly engages the primary sealing ring opposite of sealing engagement with the housing. The second sealing ring is disposed between the outward flange and the third sealing ring. The third sealing ring includes at least two ring segments. The ring-shaped insert, the second sealing ring, and the third sealing ring define a first cavity adjacent to the second sealing ring and the third sealing ring. The primary sealing ring, the second sealing ring, the outward flange, and the housing define a second cavity adjacent to the primary sealing ring. The outward flange and the second sealing ring cooperate to separate the first cavity from the second cavity.

In accordance with other embodiments of the invention, the rotatable element is a shaft.

In accordance with other embodiments of the invention, the rotatable element is a runner disposed along a shaft.

In accordance with other embodiments of the invention, when in use, the first cavity is suitable to be at a higher pressure and the second cavity is suitable to be at a lower pressure.

In accordance with other embodiments of the invention, the fluid may traverse, in use, the radial sealing surface adjacent to the third sealing ring before entering the primary sealing ring.

In accordance with other embodiments of the invention, the housing includes at least one exhaust port.

In accordance with other embodiments of the invention, a fluid originating from the higher pressure side may traverse, in use, the first cavity and pass around the second sealing ring before entering the second cavity.

In accordance with other embodiments of the invention, the third sealing ring is biased in the direction of the primary sealing ring via a spring. The spring is disposed between and directly contacts the third sealing ring and a retaining ring secured to the housing.

In accordance with other embodiments of the invention, the spring is a wave spring.

In accordance with other embodiments of the invention, an annular gap is disposed between the third sealing ring and the rotatable element.

In accordance with other embodiments of the invention, the third sealing ring is comprised of metal.

In accordance with other embodiments of the invention, a plurality of retaining pins extend at one end into the primary sealing ring and at another end into the third sealing ring.

In accordance with other embodiments of the invention, the primary sealing ring is biased outward in the direction of the rotatable element via a plurality of springs.

In accordance with other embodiments of the invention, the springs permit proper alignment of the seal segments of the primary sealing ring to accept the retaining pins.

Several exemplary advantages are possible. The invention facilitates circumferential sealing which minimizes wear along a face sealing surface, between a primary sealing ring and a housing, and along a radial sealing surface, between a primary sealing ring and a rotating shaft or runner. The invention facilitates circumferential sealing which minimizes heating along a radial sealing surface between a primary sealing ring and a rotating shaft or runner. The invention minimizes contact forces thereby reducing oil coolant requirements along a radial sealing surface between a primary sealing ring and a rotating shaft or runner. The invention reduces contact forces thereby reducing or eliminating coolant needs along a radial sealing surface between a primary sealing ring comprising ceramic and a rotating shaft or runner. Hydrostatic embodiments provide a self-adjusting force balance at the radial sealing surface.

The above and other objectives, features, and advantages of the preferred embodiments of the invention will become apparent from the following description read in connection with the accompanying drawings, in which like reference numerals designate the same or similar elements.

Additional aspects, features, and advantages of the invention will be understood and will become more readily apparent when the invention is considered in the light of the following description made in conjunction with the accompanying drawings:.

Reference will now be made in detail to several embodiments of the invention that are illustrated in the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts. The drawings are in simplified form and are not to precise scale.

While features of various embodiments are separately described, it is understood that such features are combinable to form other embodiments.

Referring now to <FIG>, a circumferential seal assembly <NUM> is shown disposed within a housing <NUM> about a rotatable element <NUM>. The circumferential seal assembly <NUM> generally comprises a primary sealing ring <NUM>, a second sealing ring <NUM>, a third sealing ring <NUM>, and an insert <NUM>. Components for the circumferential seal assembly <NUM> are secured within the housing <NUM> preferably via securing means understood in the art, non-limiting examples including a back plate <NUM> and a retaining ring <NUM>. Components of the circumferential seal assembly <NUM> are composed of materials suitable for the intended applications, examples including but not limited to metals, ceramics, and non-metals, one further non-limiting example of the latter being carbon.

Referring again to <FIG>, the circumferential seal assembly <NUM>, housing <NUM>, and rotatable element <NUM> are aligned along and disposed about a rotational axis <NUM>, often coinciding with the rotational axis within a turbine engine. The rotatable element <NUM> is broadly defined to include a rotatable shaft or the like with or without elements extending therefrom, one non-limiting example of the latter being a runner.

Referring again to <FIG>, the circumferential seal assembly <NUM>, housing <NUM>, and rotatable element <NUM> generally cooperate to define and separate a higher pressure side <NUM> and a lower pressure side <NUM>. The housing <NUM> is attached to structural components (not shown) of a turbine engine via methods understood in the art so as to secure the circumferential seal assembly <NUM> therein. In this arrangement, the circumferential seal assembly <NUM> and housing <NUM> are non-rotating. The configuration of the housing <NUM> is design dependent; however, it is understood that the housing <NUM> cooperates with the circumferential seal assembly <NUM> and the rotatable element <NUM> to define two separate compartments whereby one fluid, such as a lubricant, resides at a lower pressure within a compartment coinciding with the lower pressure side <NUM> and another fluid, such as a gas, resides at a higher pressure within a compartment coinciding with the higher pressure side <NUM>.

Referring again to <FIG>, the primary sealing ring <NUM> is disposed within the housing <NUM> so as to sealingly engage the rotatable element <NUM> along an outer surface thereof over a region referred to as the radial sealing surface <NUM>. While the radial sealing surface <NUM> is shown along the outer circumferential surface <NUM> of the rotatable element <NUM>, it is understood that the radial sealing surface <NUM> may be disposed along the inner diameter of a rotatable element <NUM>. The primary sealing ring <NUM> also sealingly engages an inside surface along the housing <NUM> over a region referred to as a face sealing surface <NUM> adjacent to the lower pressure side <NUM>. It is further understood that the face sealing surface <NUM> may be adjacent to an optional windback <NUM> which extends from the housing <NUM> into the lower pressure side <NUM>. Sealing engagement is generally understood to mean a non-contact arrangement and/or a contact arrangement that limits, prevents, or controls the flow of fluids between the higher pressure side <NUM> and the lower pressure side <NUM>. In preferred embodiments, sealing engagement may be implemented via a thin-film fluid layer. In one specific example, the thin-film layer may be disposed along a gap <NUM> between the primary sealing ring <NUM> and the rotatable element <NUM>.

Referring again to <FIG>, the primary sealing ring <NUM> has an outer surface and an inner surface. The outer circumferential surface of the primary sealing ring <NUM> includes a spring groove <NUM>. The spring groove <NUM> accepts a garter spring <NUM> which urges or biases the primary sealing ring <NUM> in the direction of the radial sealing surface <NUM>. The inner circumferential surface of the primary sealing ring <NUM> includes a seal bore dam <NUM> and an annular groove <NUM>. In preferred embodiments, the seal bore dam <NUM> is biased toward the third sealing ring <NUM> and away from the housing <NUM>.

Referring again to <FIG>, the insert <NUM> directly contacts a portion of the inner surface of the housing <NUM>. The insert <NUM> is a ring-shaped element configured to contact and thereby to be securable within the housing <NUM>. A portion of the insert <NUM> forms an inward flange <NUM> configured to extend toward but not contact the primary sealing ring <NUM>. An O-ring <NUM> is positioned between the housing <NUM> and the insert <NUM> so as to prevent fluid from completely traversing the interface therebetween.

Referring again to <FIG>, the second sealing ring <NUM> is positioned about the primary sealing ring <NUM> and adjacent to the inward flange <NUM>. The second sealing ring <NUM> sealingly engages a portion of the outer circumferential surface of the primary sealing ring <NUM>. The second sealing ring <NUM> also sealingly engages a portion of a face of the inward flange <NUM>. The second sealing ring <NUM> extends below the end of the inward flange <NUM> so as to contact the outer circumferential surface of the primary sealing ring <NUM>.

Referring again to <FIG>, the third sealing ring <NUM> is positioned so as to overlay one side of the primary sealing ring <NUM> and the second sealing ring <NUM>. The third sealing ring <NUM> is biased toward the primary sealing ring <NUM> via a plurality of compression springs <NUM>. Each compression spring <NUM> is secured at one end within a pocket <NUM> along the third sealing ring <NUM> and at another end within a pocket <NUM> along the back plate <NUM>. In preferred embodiments, the compression spring <NUM> ensures contact between the primary sealing ring <NUM> and the third sealing ring <NUM> and biases the primary sealing ring <NUM> toward the face sealing surface <NUM>. This arrangement may or may not permit contact between the third sealing ring <NUM> and the second sealing ring <NUM>. The outer circumferential surface of the third sealing ring <NUM> further includes a spring groove <NUM>. The spring groove <NUM> accepts a garter spring <NUM> which urges or biases the third sealing ring <NUM> in the direction of the radial sealing surface <NUM>.

Referring again to <FIG>, the housing <NUM> includes a groove <NUM> which accepts the retaining ring <NUM>. The back plate <NUM> is a ring-shaped element disposed between the retaining ring <NUM> and the third sealing ring <NUM>. The compression spring <NUM> secures the back plate <NUM> to the retaining ring <NUM> by pushing the back plate <NUM> into contact with the retaining ring <NUM>. In this arrangement, the compression spring <NUM> should remain sufficiently compressible so that the third sealing ring <NUM> and the primary sealing ring <NUM> are movable toward the back plate <NUM> in response to pressure forces at the face sealing surface <NUM>. A gap <NUM> is provided between the back plate <NUM> and the third sealing ring <NUM> to accommodate axial displacements of the primary sealing ring <NUM> and the third sealing ring <NUM> thereby permitting further compression of the compression spring <NUM>.

Referring again to <FIG>, the insert <NUM>, the second sealing ring <NUM>, and the third sealing ring <NUM> are configured to cooperate to surround a region referred to as a first cavity <NUM>. The first cavity <NUM> is communicable with the higher pressure side <NUM> via the gap <NUM>. The gap <NUM> permits exchange of fluid between the first cavity <NUM> and the higher pressure side <NUM>.

Referring again to <FIG>, the primary sealing ring <NUM>, the second sealing ring <NUM>, the insert <NUM>, and the housing <NUM> are configured to cooperate to enclose a region referred to as a second cavity <NUM>. The second cavity <NUM> is communicable with the lower pressure side <NUM> via at least one exhaust port <NUM> along the housing <NUM>. The exhaust port <NUM> is a hole disposed through the housing <NUM> which permits exchange of fluid between the second cavity <NUM> and the lower pressure side <NUM>.

Referring again to <FIG>, the second sealing ring <NUM> and the insert <NUM> are disposed between the first cavity <NUM> and the second cavity <NUM>. This arrangement ensures separation between the first cavity <NUM> and the second cavity <NUM> thereby preventing fluids originating in the higher pressure side <NUM> from bypassing and negating the sealing function of the circumferential seal assembly <NUM>. However, it is understood that fluid may slowly bleed across the interface formed between the second sealing ring <NUM> and each of the primary sealing ring <NUM>, the third sealing ring <NUM>, and the insert <NUM>.

Referring now to <FIG>, the primary sealing ring <NUM> in <FIG> is comprised of two or more seal segments <NUM> which in combination form a ring-shaped structure referred to as a segmented ring. Each seal segment <NUM> includes a vertical flange <NUM> at one end of a horizontal flange <NUM>. This arrangement defines a generally L-shaped cross section for the seal segment <NUM>. The vertical flange <NUM> extends in an outward radial direction from the horizontal flange <NUM>. The vertical flange <NUM> and the horizontal flange <NUM> are curved so as to form a ring-shaped vertical flange <NUM> and a ring-shaped horizontal flange <NUM> when two or more seal segments <NUM> are combined. A first end <NUM> and a second end <NUM> of the seal segment <NUM> may include features facilitating an interlocking engagement between adjoining seal segments <NUM>. In some embodiments, the interlock may be implemented by a tongue and a groove arrangement such as in <FIG>; however, it is understood that other interlocking means are also applicable as generally illustrated by the first end <NUM> and the second end <NUM> in <FIG>.

Referring again to <FIG>, the seal segment <NUM> includes an inlet side <NUM> and an outlet side <NUM>. The inlet side <NUM> is disposed along the horizontal flange <NUM> opposite of the vertical flange <NUM>. The inlet side <NUM> is oriented toward the higher pressure side <NUM> in <FIG>. An outlet side <NUM> is disposed along the vertical flange <NUM> opposite the horizontal flange <NUM>. The outlet side <NUM> is oriented toward the lower pressure side <NUM> in <FIG>. At least one vertical feed groove <NUM> extends across a portion of the inlet side <NUM> from the inner surface <NUM>. At least one vent channel <NUM> extends into the seal segment <NUM> from the outer surface <NUM> adjacent to the intersection between the horizontal flange <NUM> and the vertical flange <NUM>. A vertical groove <NUM> is positioned along the vertical flange <NUM> and is aligned with the vent channel <NUM>.

Referring now to <FIG> and <FIG>, the vertical feed groove <NUM> extends outward from the inner surface <NUM> in the direction of the outer surface <NUM>. The vertical feed groove <NUM> intersects one end of a first channel <NUM> at the inlet side <NUM>. Another end of the first channel <NUM> intersects the outlet side <NUM>. In preferred embodiments, the outlet side <NUM> has a pocket <NUM> that intersects the first channel <NUM>. At least one optional second channel <NUM> may extend into the seal segment <NUM> from the outlet side <NUM>, preferably intersecting the pocket <NUM>. The number, arrangement, and size of the first channel <NUM> and the second channel <NUM> are design dependent based on the flow requirements at the radial sealing surface <NUM> and the face sealing surface <NUM>.

Referring now to <FIG>, the inner surface <NUM> of the seal segment <NUM> may include features which facilitate sealing along the radial sealing surface <NUM>. For example, the outlet of the second channel <NUM> may intersect the inner surface <NUM>, preferably at a pad <NUM>. In another example, a bore groove <NUM> may be interposed between adjoining pads <NUM>. The bore groove <NUM> may also intersect the annular groove <NUM>, the latter interposed between the pads <NUM> and the seal bore dam <NUM>. The arrangement between bore grooves <NUM> and annular groove <NUM> permits fluid from the lower pressure side <NUM> to pass under the seal segment <NUM>.

Referring now to <FIG>, vertical feed groove <NUM>, first channel <NUM>, and pocket <NUM> are contiguous so as to form a pathway across the seal segment <NUM> between the inlet side <NUM> and the outlet side <NUM>. The seal bore dam <NUM> is interposed between the vertical feed groove <NUM> and the annular groove <NUM>. The bore groove <NUM> and the annular groove <NUM> are contiguous so as to form a pathway along the inner surface <NUM> across the vertical flange <NUM> and a portion of the horizontal flange <NUM>.

Referring now to <FIG>, pocket <NUM> and second channel <NUM> are contiguous so as to form a pathway across the seal segment <NUM> between the outlet side <NUM> and the inner surface <NUM>. Although the second channel <NUM> is shown composed of intersecting linear segments, it is understood that the second channel <NUM> may consist of one or more linear or nonlinear cavities that permit flow of a fluid from the outlet side <NUM> to the inner surface <NUM>. While the first channel <NUM> and the second channel <NUM> may communicate with the same pocket <NUM>, each of the first channel <NUM> and the second channel <NUM> is separately disposed within the seal segment <NUM>. Therefore, it is understood that the arrangement of the first channel <NUM> in <FIG> and the second channel <NUM> in <FIG> permits a fluid to pass through the first channel <NUM> before exiting into the pocket <NUM> where the fluid is then redirected into and through the second channel <NUM>.

Referring now to <FIG>, a vent channel <NUM> forms a pathway across the horizontal flange <NUM> of the seal segment <NUM> from the inner surface <NUM> to the outer surface <NUM>. In preferred embodiments, one end of the vent channel <NUM> may intersect the annular groove <NUM> and the other end may intersect the outer surface <NUM> adjacent to the spring groove <NUM>. The vent channel <NUM> facilitates venting of fluid otherwise communicated onto the radial sealing surface <NUM>. For example, the vent channel <NUM> permits fluid communicated onto the inner surface <NUM> via the second channel <NUM> or via the bore groove <NUM> into the annular groove <NUM> to traverse the seal segment <NUM> before entering the second cavity <NUM>.

Referring now to <FIG>, at least one anti-rotation pin <NUM> may be disposed within the housing <NUM>. The anti-rotation pin <NUM> is secured to the housing <NUM> via threaded or press fit engagement and positioned so as to extend into the housing <NUM> adjacent to the primary sealing ring <NUM>. The anti-rotation pin <NUM> extends into a pocket <NUM> disposed along a seal segment <NUM>. The anti-rotation pin <NUM> mechanically engages the seal segment <NUM> at the pocket <NUM> so as to prevent relative rotational motion between the primary sealing ring <NUM> and the housing <NUM>. The pocket <NUM> may be positioned along the seal segment <NUM> as shown in <FIG> or positioned at or adjacent to a joint <NUM> between adjoining seal segments <NUM>.

Referring now to <FIG>, the second sealing ring <NUM> is preferred to be a contiguous ring-shaped element with a single gap <NUM>. The contiguousness of the second sealing ring <NUM> restricts fluid from passing between joints along the otherwise segmented third sealing ring <NUM>. The gap <NUM> facilitates expansion of the second sealing ring <NUM> during assembly onto and disassembly from other components comprising the circumferential seal assembly <NUM>. The higher pressure side <NUM> of the second sealing <NUM> may contact or nearly contact the third sealing ring <NUM>, the latter illustrated by the gap <NUM> in <FIG>. The gap <NUM> may be sized to the maximum wear along the primary sealing ring <NUM> at the face sealing surface <NUM> over the anticipated lifetime of the primary sealing ring <NUM>. In some embodiments, the second sealing ring <NUM> may sealingly engage the third sealing ring <NUM>.

Referring again to <FIG>, it may be advantageous in some embodiments for the second sealing ring <NUM> to further include a face groove <NUM> communicable with one or more feed grooves <NUM> at the lower pressure side <NUM>. The face groove <NUM> and feed groove <NUM> may be positioned along the interface between the insert <NUM> and the second sealing ring <NUM>, as shown in <FIG>. This arrangement permits fluid within the first cavity <NUM> to flow in the face groove <NUM> via the feed groove(s) <NUM> so as to enhance sealing engagement between the insert <NUM> and the second sealing ring <NUM>. It may also be advantageous to provide one or more pockets <NUM> along the inner circumferential surface of the second sealing ring <NUM>, as generally represented in <FIG>, to enhance sealing at the interface with the primary sealing ring <NUM>.

Referring now to <FIG>, the third sealing ring <NUM> comprises at least two ring segments <NUM> disposed in an end-to-end arrangement forming a ring-shaped structure. The ends of adjoining ring segments <NUM> may include interlockable features, such as described in <FIG>, at each joint <NUM>. In preferred embodiments, the joints <NUM> along the third sealing ring <NUM> are offset from the joints <NUM> along the primary sealing ring <NUM> to minimize leakage across the circumferential seal assembly <NUM>.

Referring again to <FIG>, each ring segment <NUM> may include one or more pockets <NUM> along a face adjacent to the back plate <NUM>. The pocket <NUM> accepts the compression spring <NUM> so that a portion of the compression spring <NUM> partially extends from the pocket <NUM>. Each compression spring <NUM> biases the third sealing ring <NUM> onto the primary sealing ring <NUM> and biases the back plate <NUM> onto the retaining ring <NUM> as described in <FIG>.

Referring now to <FIG> and <FIG>, each ring segment <NUM> has one or more bore grooves <NUM>. The bore groove <NUM> traverses the ring segment <NUM> at the inner radial surface thereof. The bore groove <NUM> permits fluid originating in the higher pressure side <NUM> to traverse the ring segment <NUM> before entering the primary sealing ring <NUM>. Fluid within the bore groove <NUM> may oppose the inward force applied by the garter spring <NUM> along the spring groove <NUM> thereby reducing the resultant load force between the third sealing ring <NUM> and the radial sealing surface <NUM> or separating the third sealing ring <NUM> from the radial sealing surface <NUM>.

Referring again to <FIG> and <FIG>, the back plate <NUM> is a ring-shaped element disposed between the third sealing ring <NUM> and the retaining ring <NUM>. The back plate <NUM> is arranged to permit indirect contact with the third sealing ring <NUM> via the compression springs <NUM> and direct contact with the retaining ring <NUM>. However, it is understood in some embodiments that the third sealing ring <NUM> may translate within the circumferential seal assembly <NUM> so as to compress the compression springs <NUM> with or without contacting the back plate <NUM>.

Referring now to <FIG>, <FIG> and <FIG>, the back plate <NUM> is preferred to not rotate with respect to the circumferential seal assembly <NUM> and the housing <NUM>. The back plate <NUM> may include an anti-rotation tab <NUM> which extends radially outward therefrom. The anti-rotation tab <NUM> engages a complementary slot (not shown) along the housing <NUM> so as to prevent relative rotation between the back plate <NUM> and the circumferential seal assembly <NUM>. The back plate <NUM> may also include an anti-rotation tab <NUM> which extends axially from a face adjacent to the third sealing ring <NUM>. The anti-rotation tab <NUM> may engage a slot <NUM> or the like at a gap between two adjoining ring segments <NUM> along the third sealing ring <NUM> to prevent relative rotation between the third sealing ring <NUM> and the back plate <NUM>.

Referring again to <FIG> and <FIG>, the retaining ring <NUM> is a ring-shaped element with an end gap <NUM>. The retaining ring <NUM> should be sufficiently flexible so that the opening at the end gap <NUM> may be closed thereby reducing the outer diameter of the retaining ring <NUM> for assembly onto the groove <NUM>. The retaining ring <NUM> should also be sufficiently resilient permitting the end gap <NUM> to return its original shape when compressive forces are removed so that the retaining ring <NUM> properly seats onto the groove <NUM>.

Referring now to <FIG>, the circumferential seal assembly <NUM> is shown disposed within a rotatable element <NUM> rotatable about a rotational axis <NUM>. In this embodiment, the rotatable element <NUM> is disposed about the circumferential seal assembly <NUM> so that at least the primary sealing ring <NUM> sealingly engages the inner circumferential surface <NUM> of the rotatable element <NUM> along a region referred to as the radial sealing surface <NUM> between a higher pressure side <NUM> and a lower pressure side <NUM>.

Referring again to <FIG>, one or more compression springs <NUM> may be disposed between each seal segment of the primary sealing ring <NUM> and the insert <NUM>. One end of a compression spring <NUM> may be recessed within the insert <NUM> so that a second end of the compression spring <NUM> extends therefrom. The second end contacts the primary sealing ring <NUM> thereby communicating a biasing force onto each segment in the direction of the rotatable element <NUM>. In this embodiment, the compression springs <NUM> push the segments comprising the primary sealing ring <NUM> outward so that the primary sealing ring <NUM> favors expansion rather than contraction. The primary sealing ring <NUM>, the second sealing ring <NUM>, the third sealing ring <NUM>, and the insert <NUM> cooperate to define the first cavity <NUM> and the second cavity <NUM>, as otherwise described herein.

Referring again to <FIG>, the third sealing ring <NUM> in some embodiments may facilitate elimination of the back plate <NUM>. The third sealing ring <NUM> may be a ring-shaped, metal element with an inward face that sealingly engages the primary sealing ring <NUM> and the second sealing ring <NUM>. A spring <NUM> may contact the outward face of the third sealing ring <NUM>. By way of example, the spring <NUM> may be a wave spring which contacts at one end the third sealing ring <NUM> and at another end the retaining ring <NUM>. The retaining ring <NUM> is secured to the housing <NUM> as described herein thereby allowing the spring <NUM> to push or bias the third sealing ring <NUM> into engagement with the primary sealing ring <NUM>.

Referring again to <FIG>, optional retaining pins <NUM> may extend at one end into the primary sealing ring <NUM> and at another end into the third sealing ring <NUM> about the interface therebetween. During assembly, the compression springs <NUM> are seated onto the insert <NUM> and segments comprising the primary sealing ring <NUM> are placed about the compression springs <NUM>. A compressive force is applied onto the compression springs <NUM> via the sealing segments so as to properly align the segments with the retaining pins <NUM>. The retaining pins <NUM> engage cavities along the sealing segments so as to allow the retaining pins <NUM> to hold the segments in place. Optional anti-rotation paddle pins (not shown) could be pressed into the seal housing <NUM> adjacent to the sealing face and aligned to engage the primary sealing ring <NUM>. Both retaining pins <NUM> and anti-rotation pins should permit the primary sealing ring <NUM> to expand and contract as required to ensure proper sealing along the radial sealing surface <NUM>.

Referring again to <FIG>, the third sealing ring <NUM> is disposed about the rotatable element <NUM> with an annular gap <NUM> therebetween. This arrangement is advantageous in that it avoids heating and wear along the outer surface of the third sealing ring <NUM> and along the inner circumferential surface <NUM>. However, it is understood that an annular gap <NUM> may not be required in this and other embodiments of the invention thereby permitting the third sealing ring <NUM> to contact the rotatable element <NUM>. By way of examples, a primary sealing ring <NUM> with tongue/socket joints may be used with a third sealing ring <NUM> with or without an annular gap <NUM>, whereas a primary sealing ring <NUM> with radially overlapping joints would permit too much fluid to traverse the circumferential seal assembly <NUM> thereby requiring contact between the third sealing ring <NUM> and a rotatable element <NUM> along the radial sealing surface <NUM>. Contacting arrangements may permit the third sealing ring <NUM> to be composed of carbon or other material(s) suitable for contact sealing.

Referring now to <FIG>, the insert <NUM> in some embodiments may be integral with the housing <NUM> rather than a separate component from the housing <NUM>. In these embodiments, the insert <NUM> may be a part of the housing <NUM> or fixed to the housing <NUM> so as to be non-separable therefrom. In the former embodiments, the insert <NUM> may be directly formed onto the housing <NUM>. In the latter embodiments, the insert <NUM> may be fabricated separate from the housing <NUM> and then secured thereto via a weld or other methods understood in the art. The inward flange <NUM> extends toward the primary sealing ring <NUM> and cooperates with the primary sealing ring <NUM>, the second sealing ring <NUM>, and the third sealing ring <NUM> to define the first cavity <NUM> and the second cavity <NUM>, as otherwise described herein.

Referring again to <FIG>, the insert <NUM> may complicate assembly of the circumferential seal assembly <NUM> when the inner diameter of the inward flange <NUM> is smaller than the outer diameter of the primary sealing ring <NUM>. In these embodiments, the primary sealing ring <NUM> is assembled onto the housing <NUM> by inserting less than all segments of the primary sealing ring <NUM> into the housing <NUM>. The garter spring <NUM> is placed about the portion of the primary sealing ring <NUM> residing within the housing <NUM>. The remaining segment(s) of the primary sealing ring <NUM> are then inserted into housing <NUM> and the garter spring <NUM> is expanded so as to accept each segment now properly positioned to complete the primary sealing ring <NUM>. Thereafter, the garter spring <NUM> is released so as to contract onto all seal segments thereby maintaining the ring shape of the primary sealing ring <NUM>.

Referring now to <FIG> and <FIG>, pressures and pressure forces applied by fluid originating at the higher pressure side <NUM> are illustrated along a primary sealing ring <NUM> that sealingly contacts the radial sealing surface <NUM> and the face sealing surface <NUM>. The pressure loading in <FIG> is generally understood to be the pressure differential across the circumferential seal assembly <NUM> (P<NUM> -P<NUM>) with applicable decay due to leakage where P<NUM> is the pressure within the higher pressure side <NUM> and P<NUM> is the pressure within the lower pressure side <NUM>.

Referring again to <FIG> and <FIG>, the resultant force load at the radial sealing surface <NUM> is equal to the total of the spring force F<NUM> and the inward radial pressure force F<NUM> less the outward radial pressure force F<NUM> for a primary sealing ring <NUM> designed to contact a radial sealing surface <NUM>. The spring force F<NUM> is applied onto the primary sealing ring <NUM> via the garter spring <NUM>. The inward radial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by the second sealing ring <NUM> in response to fluid within the first cavity <NUM> acting on the second sealing ring <NUM>. The outward radial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by fluid at the vertical feed grooves <NUM> and the seal bore dams <NUM>.

Referring again to <FIG> and <FIG>, the resultant force load at the face sealing surface <NUM> is equal to the total of the aft axial pressure force F<NUM> and the spring force F<NUM> less the forward axial pressure force F<NUM>. The aft axial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by the third sealing ring <NUM> in response to fluid within the gap <NUM> acting on the third sealing ring <NUM>. The spring force F<NUM> is applied onto the primary sealing ring <NUM> via the compression springs <NUM>. The forward axial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by fluid communicated onto the face sealing surface <NUM> via the first channels <NUM>.

Referring now to <FIG>, exemplary flow paths are shown through a circumferential seal assembly <NUM> whereby fluid originating at a higher pressure side <NUM> at a higher pressure P<NUM> is utilized for sealing purposes before the same fluid exits the circumferential seal assembly <NUM> and enters a lower pressure side <NUM> at a lower pressure P<NUM>. It understood that fluid communicated onto the face sealing surface <NUM> and the radial sealing surface <NUM> may form a thin-film layer. The thin-film layer may enhance sealing function by the primary sealing ring <NUM> disposed about the rotatable element <NUM> along a rotational axis <NUM> and reduce pressure forces along the primary sealing ring <NUM> at the face sealing surface <NUM> and the radial sealing surface <NUM>.

Referring again to <FIG>, fluid from the higher pressure side <NUM> passes through an annular opening between the retaining ring <NUM> and the rotatable element <NUM> and another annular opening between the back plate <NUM> and the rotatable element <NUM>. The fluid then passes along the gap <NUM> between the back plate <NUM> and the third sealing ring <NUM> before entering the first cavity <NUM>. In some embodiments, fluid may then partially or completely traverse one or more interfaces between the second sealing ring <NUM> and the insert <NUM>, the third sealing ring <NUM> and the primary sealing ring <NUM> before entering the second cavity <NUM>. It is understood that the flow rate, if any, between the first cavity <NUM> and the second cavity <NUM> is substantially less than the flow rate across other portions of the circumferential seal assembly <NUM>.

Referring again to <FIG>, fluid also passes across the third sealing ring <NUM> via the bore grooves <NUM> before entering the vertical feed grooves <NUM>. A portion of the fluid may pass under the seal bore dam <NUM> and thereafter enter the annular groove <NUM>. Fluid within the vertical feed grooves <NUM> then enters and passes through the first channels <NUM> before exiting into the pocket <NUM>. A portion of the fluid within the pocket <NUM> may then separate and flow across the face sealing surface <NUM> thereafter entering the second cavity <NUM> and the lower pressure side <NUM> via an annular opening adjacent to the windback <NUM>. Another portion of the fluid within the pocket <NUM> may then enter the second channels <NUM> before exiting the primary sealing ring <NUM> along the pads <NUM>. Fluid along the pads <NUM> may then separate and flow between the bore surface <NUM> along the primary sealing ring <NUM> and the radial sealing surface <NUM> before either entering the annular groove <NUM> or passing into the lower pressure side <NUM> adjacent to the windback <NUM>. In some embodiments, fluid may be communicated via the second channels <NUM> into the bore grooves <NUM> along the seal segments <NUM> and/or optional bearing slots <NUM> along the bore surface <NUM>.

Referring again to <FIG>, fluid within the annular groove <NUM> then passes into the vent channels <NUM> before exiting into the second cavity <NUM>. Fluid within the second cavity <NUM> passes through the exhaust port(s) <NUM> along the housing <NUM> before entering the lower pressure side <NUM>.

Referring now to <FIG>, <FIG> and <FIG>, pressures and pressure forces applied by fluid originating in the higher pressure side <NUM> are illustrated along a primary sealing ring <NUM> that sealingly engages the radial sealing surface <NUM> via a thin-film along the gap <NUM> and sealingly contacts the face sealing surface <NUM>. The pressure loading in <FIG> is generally understood to be the pressure differential across the circumferential seal assembly <NUM> (P<NUM> - P<NUM>) with applicable decay due to leakage where P<NUM> is the pressure within the higher pressure side <NUM> and P<NUM> is the pressure within the lower pressure side <NUM>.

Referring again to <FIG>, <FIG> and <FIG>, the resultant force load at the radial sealing surface <NUM> is equal to the total of the spring force F<NUM> and the inward radial pressure force F<NUM> less the total of the outward radial pressure force F<NUM> and the outward radial pressure force F<NUM>. The spring force F<NUM> is applied onto the primary sealing ring <NUM> via the garter spring <NUM>. The inward radial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by the second sealing ring <NUM> in response to fluid within the first cavity <NUM> acting on the second sealing ring <NUM>. The outward radial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by fluid at the vertical feed grooves <NUM> and the seal bore dams <NUM>. The outward radial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by fluid hydrostatically communicated at the pad <NUM> via the second channels <NUM>.

Referring again to <FIG>, <FIG> and <FIG>, the resultant force load at the face sealing surface <NUM> is equal to the total of the aft axial pressure force F<NUM> and the spring force F<NUM> less the forward axial pressure force F<NUM>. The aft axial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by the third sealing ring <NUM> in response to fluid within the gap <NUM> acting on the third sealing ring <NUM>. The spring force F<NUM> is applied onto the primary sealing ring <NUM> via the compression springs <NUM>. The forward axial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by fluid communicated onto the face sealing surface <NUM> via the first channels <NUM>.

Referring now to <FIG>, exemplary flow paths are shown through a circumferential seal assembly <NUM> whereby fluid originating at a higher pressure side <NUM> at a higher pressure P<NUM> is utilized for sealing purposes before the same fluid exits the circumferential seal assembly <NUM> and enters a lower pressure side <NUM> at a lower pressure P<NUM>. It understood that fluid communicated onto the face sealing surface <NUM> and the radial sealing surface <NUM> may form a thin-film layer enhancing sealing function by the primary sealing ring <NUM> along the rotatable element <NUM>, such as the runner disposed about a rotational axis <NUM> in <FIG>, and reducing pressure forces along the primary sealing ring <NUM> at the face sealing surface <NUM> and the radial sealing surface <NUM>.

Referring again to <FIG>, fluid also passes across the third sealing ring <NUM> via the bore grooves <NUM> before entering the vertical feed grooves <NUM>. A portion of the fluid may pass under the seal bore dam <NUM> and before entering the annular groove <NUM>. Fluid within the vertical feed grooves <NUM> then enters and passes through the first channels <NUM> before exiting into the pocket <NUM>. The fluid within the pocket <NUM> may then separate and flow across the face sealing surface <NUM> thereafter entering the second cavity <NUM> and the lower pressure side <NUM> via an annular opening adjacent to the windback <NUM>.

Referring again to <FIG>, the rotatable element <NUM> may include a plurality of hydrodynamic grooves <NUM> disposed along the radial sealing surface <NUM>. A first end <NUM> of the hydrodynamic groove <NUM> communicates with fluid at the higher pressure side <NUM>. The hydrodynamic groove <NUM> is oriented with respect to rotation of the rotatable element <NUM> so that fluid is captured at the first end <NUM> thereafter traveling along the hydrodynamic groove <NUM> with increasing pressure. The fluid is then redirected upward at a second end <NUM> of the hydrodynamic groove <NUM> onto the primary sealing ring <NUM>, preferably at the end with the pad <NUM>. Fluid along the pads <NUM> may flow into the lower pressure side <NUM> and/or the annular groove <NUM>.

Referring again to <FIG>, <FIG> and <FIG>, the resultant force load at the radial sealing surface <NUM> is equal to the total of the spring force F<NUM> and the inward radial pressure force F<NUM> less the total of the outward radial pressure force F<NUM> and the outward radial pressure force F<NUM>. The spring force F<NUM> is applied onto the primary sealing ring <NUM> via the garter spring <NUM>. The inward radial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by the second sealing ring <NUM> in response to fluid within the first cavity <NUM> acting on the second sealing ring <NUM>. The outward radial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by fluid at the vertical feed grooves <NUM> and the seal bore dams <NUM>. The outward radial pressure force F<NUM> is applied onto the primary sealing ring <NUM> by fluid hydrodynamically communicated at the pad <NUM> via the hydrodynamic grooves <NUM>.

Referring now to <FIG>, <FIG> and <FIG>, the resultant pressure force at the face sealing surface <NUM> is adjusted via changes to the radial height Y of the primary sealing ring <NUM>. The resultant pressure force increases when the radial height Y is decreased by a radial adjustment ΔY causing a corresponding decrease to the forward axial pressure force F<NUM>. The resultant pressure force decreases when the radial height Y is increased by a radial adjustment ΔY causing a corresponding increase to the forward axial pressure force F<NUM>.

Referring now to <FIG>, the resultant pressure forces at the face sealing surface <NUM> are illustrated in exemplary form whereby axial unit load is plotted over a range of pressure differentials across a standard circumferential seal such as in <FIG> and an improved contacting circumferential seal such as in <FIG>. The improved seal with a radial height Y significantly reduces the axial unit load in comparison to the standard seal whereby the reductions achievable by the improved seal are greater at higher pressure differentials. The curves for radial adjustments ±ΔY within an exemplary range demonstrate that the reduction in the axial load profile does not sacrifice the adjustability required to optimize the circumferential seal assembly <NUM> for particular applications.

Referring again to <FIG>, <FIG> and <FIG>, the resultant pressure force at the radial sealing surface <NUM> is adjusted via changes to the relative position of the second sealing ring <NUM> with respect to the seal bore dam <NUM>. Adjustments made to the second sealing ring <NUM> may require dimensional and positional adjustments to the insert <NUM> so as to maintain the proper sealing engagement therebetween.

Referring again to <FIG>, <FIG> and <FIG>, the magnitude of the resultant pressure force increases when the axial position of the second sealing ring <NUM> is adjusted toward the lower pressure side <NUM>. The adjustment ΔX is implemented by reducing the axial distance between the second sealing ring <NUM> and the lower pressure side <NUM> so that the axial width X over which the inward radial pressure force F<NUM> acts is increased. In one example, the second sealing ring <NUM> may be physically moved toward the lower pressure side <NUM> without adjustment to the axial width of the second sealing ring <NUM>.

Referring again to <FIG>, <FIG> and <FIG>, the magnitude of the resultant pressure force decreases when the axial position of the second sealing ring <NUM> is moved toward the higher pressure side <NUM>. The adjustment ΔX is implemented by increasing the axial distance between the second sealing ring <NUM> and the lower pressure side <NUM> so that the axial width X over which the inward radial pressure force F<NUM> acts is decreased. In one example, the second sealing ring <NUM> may be physically moved toward the higher pressure side <NUM> without adjustment to the axial width of the second sealing ring <NUM>.

Referring again to <FIG>, <FIG> and <FIG>, the face <NUM> of the second sealing ring <NUM> is either aligned with the face <NUM> of the seal bore dam <NUM> or closer to the higher pressure side <NUM> than the face <NUM> in preferred embodiments so that an adjustment ΔX to the second sealing ring <NUM> in the direction of the lower pressure side <NUM> decreases the axial distance between the faces <NUM>, <NUM> and so that an adjustment ΔX in the direction of the higher pressure side <NUM> increases the axial distance between the faces <NUM>, <NUM>.

Referring now to <FIG>, the resultant pressure force at the radial sealing surface <NUM> is illustrated in exemplary form whereby radial unit load is plotted over a range of pressure differentials across a standard circumferential seal such as in <FIG> and an improved contacting circumferential seal such as in <FIG>. The improved seal significantly reduces the radial unit load in comparison to the standard seal whereby the reductions achievable by the improved seal are greater at higher pressure differentials. The curves for adjustments ΔX within an exemplary range demonstrate that the reduction in the radial load profile does not sacrifice the adjustability required to optimize the circumferential seal assembly <NUM> for particular applications. It is understood from <FIG> that additional improvements are realized by inclusion of the hydrostatic lift in <FIG> and/or the hydrodynamic lift in <FIG>.

The description above indicates that a great degree of flexibility is offered in terms of the present invention. Although various embodiments have been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.

Claim 1:
A circumferential seal assembly (<NUM>) for use between a higher pressure side (<NUM>) and a lower pressure side (<NUM>) comprising:
(a) a primary sealing ring (<NUM>) disposed within a housing (<NUM>) along a rotatable element (<NUM>), said primary sealing ring (<NUM>) sealingly engages both a face sealing surface of said housing (<NUM>) and a radial sealing surface (<NUM>) of said rotatable element (<NUM>), said primary sealing ring (<NUM>) includes at least two seal segments (<NUM>);
(b) a ring-shaped insert (<NUM>) secured within said housing (<NUM>) and/or being integral with said housing (<NUM>), a portion of said ring-shaped insert (<NUM>) forming an outward flange extending toward but not contacting said primary sealing ring (<NUM>);
(c) a second sealing ring (<NUM>) positioned within said primary sealing ring (<NUM>), said second sealing ring (<NUM>) sealingly engaging a portion of a face of said outward flange, said second sealing ring (<NUM>) extending past the end of said outward flange so as to contact an inner circumferential surface of said primary sealing ring (<NUM>); and
(d) a third sealing ring (<NUM>) which contacts and sealingly engages said primary sealing ring (<NUM>) opposite of sealing engagement with said housing (<NUM>), said second sealing ring (<NUM>) being disposed between said outward flange and said third sealing ring (<NUM>), said third sealing ring (<NUM>) including at least two ring segments (<NUM>);
wherein
said ring-shaped insert (<NUM>), said second sealing ring (<NUM>), and said third sealing ring (<NUM>) define a first cavity (<NUM>) adjacent to said second sealing ring (<NUM>) and said third sealing ring (<NUM>);
said primary sealing ring (<NUM>), said second sealing ring (<NUM>), said outward flange, and said housing (<NUM>) define a second cavity (<NUM>) adjacent to said primary sealing ring (<NUM>);
said outward flange and said second sealing ring (<NUM>) cooperate to separate said first cavity (<NUM>) from said second cavity (<NUM>).