Rotary seals

Abstract

A rotary joint for use along an incompressible fluid path between a rotating machine component and a non-rotating machine component includes a non-rotating seal carrier including a non-rotating seal that together with the non-rotating seal carrier defines an inner net hydraulic surface and an outer net pneumatic surface. Contact of the incompressible fluid under pressure with the net hydraulic surface generates a closing force, and contact of the compressible fluid under pressure with the net pneumatic surface generates an opening force.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Provisional U.S. Patent Application No. 62 / 725,766, filed on August 31, 2018, and entitled “Swivel Joint.” Background Art

[0003] In machine tools, a spindle can be described as a device that includes a rotating shaft or spindle that typically carries a cutting or other tool. Depending on the type of machine, the spindle can be driven by various types of power to rotate the shaft or shaft, such as an electric motor, hydraulic or pneumatic motor, etc. In applications where pneumatic power is used to drive the shaft, the shaft may include turbine blades connected to the shaft and enclosed in a housing of a spindle, which has a scrolled or other shape that forces air provided at high pressure to pass through the blades to rotate the shaft. Under typical operating conditions, pressurized air is supplied, such as 90psi, and the shaft is rotated at a high speed, such as 65,000RPM. In machines for forming parts, such as CNC machines, so-called air turbine shafts are known.

[0004] While air turbine shafts are useful in providing high speed shafts that can perform machining operations, their high speed operation can generate heat between the shaft tool and the workpiece, which is typically addressed by providing an external flow of coolant that both cools the workpiece and removes debris. However, positioning of the coolant flow onto areas of the workpiece is not always optimal, or even possible, particularly when machining areas within narrow cavities of the workpiece. Summary of the invention

[0005] In one aspect, the present invention describes a rotary joint that is arranged along an incompressible fluid path between a rotating mechanical component and a non-rotating mechanical component. The rotary joint includes a mounting sleeve that is arranged in a hole formed in the non-rotating mechanical component. The mounting sleeve forms a sliding hole in which a non-rotating seal carrier is slidably and sealingly arranged. The non-rotating seal carrier includes a non-rotating seal element that defines an inner net hydraulic surface and an outer net pneumatic surface together with the non-rotating seal carrier. The rotating seal element is arranged on the rotating mechanical component. The non-rotating seal carrier is axially movable between an extended position and a retracted position, in which the rotating and non-rotating seal elements contact to form a mechanical face seal, and in which the rotating and non-rotating seal elements separate to form a gap in the axial direction. During operation, the contact of the incompressible fluid under pressure with the net hydraulic surface generates a closing force in a closing direction that tends to push the non-rotating seal carrier from the retracted position toward the extended position. Furthermore, during operation, contact of the compressible fluid under pressure with the net aerodynamic surface generates an opening force in an opening direction that tends to urge the non-rotating seal carrier from the extended position to the retracted position.

[0006] In another aspect, the present invention describes a method for operating a rotary joint. The method includes providing a non-rotating seal carrier slidably and sealably disposed within a sliding bore, the non-rotating seal carrier including a non-rotating seal element; defining a net hydraulic surface on the inner side of the non-rotating seal element and the non-rotating seal carrier; defining a net pneumatic surface on the outer side of the non-rotating seal element and the non-rotating seal carrier; providing a rotating seal element disposed on a rotating mechanical component; and moving the non-rotating seal carrier in an axial direction between an extended position and a retracted position, in which the rotating seal element and the non-rotating seal element contact to form a mechanical face seal, and in which the rotating seal element and the non-rotating seal element separate to form a gap in the axial direction. In one embodiment, the movement from the retracted position to the extended position is accomplished by providing an incompressible fluid in contact with the net hydraulic surface to generate a closing force in a closing direction, and the movement from the extended position to the retracted position is accomplished by providing a compressible fluid in contact with the net pneumatic surface to generate an opening force in an opening direction.

[0007] In yet another aspect, the present invention describes a rotary joint disposed along an incompressible fluid path between a rotating mechanical component and a non-rotating mechanical component. The rotary joint includes a mounting sleeve disposed in a hole formed in the non-rotating mechanical component, the mounting sleeve forming a sliding hole, a non-rotating seal carrier slidably and sealably disposed in the sliding hole, the non-rotating seal carrier including a non-rotating seal element, wherein the non-rotating seal element and the non-rotating seal carrier define a net hydraulic surface on the inside and a net pneumatic surface on the outside, a rotating seal element disposed on the rotating mechanical component, and a spring disposed between the mounting sleeve and the non-rotating seal carrier, the spring providing a spring force to the non-rotating seal carrier. The non-rotating seal carrier is movable in an axial direction between an extended position and a retracted position during operation, in which the rotating and non-rotating seal elements contact to form a mechanical face seal, and in which the rotating and non-rotating seal elements separate to form a gap in the axial direction. The contact of the incompressible fluid under pressure with the net hydraulic surface and the spring generates a closing hydraulic force and a spring force in a closing direction that tend to urge the non-rotating seal carrier from the retracted position toward the extended position, and the contact of the compressible fluid under pressure with the net pneumatic surface generates an opening force in an opening direction that tends to urge the non-rotating seal carrier from the extended position toward the retracted position. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a cross-sectional view through an air spindle showing the rotary seal in a closed position according to the present invention; and

[0009] Figure 2 yes Figure 1 A cross-sectional view of the air spindle showing the rotary seal in the open position.

[0010] Figure 3 and Figure 4 is a schematic diagram of the forces acting on the sealing ring under different operating conditions of the rotating main shaft according to the present invention.

[0011] Figure 5 is a cross-sectional view through an air spindle having a closing spring according to an alternative embodiment of the present invention. DETAILED DESCRIPTION

[0012] The present invention relates to a rotary seal for a coolant channel extending through an air spindle. The air spindle according to the present invention is advantageously configured to allow fluid coolant to pass through the spindle during machining, so that a more reliable and precise arrangement of the coolant flow can be achieved. Given the relatively high rotational speed of the spindle's shaft, the rotary seal is configured to produce a seal when liquid coolant is provided through the shaft, and to pop out or produce a gap between the sealing rings of the rotary seal when the coolant flow is interrupted, so that damage to the seal due to dry running conditions and / or heating of the sealing rings can be avoided. It is well known that rotary seals that produce mechanical face seals, commonly known as "rotary joints", are prone to heating and may be damaged when running at high speeds without cooling and / or lubricating media. In the structure described herein, the pneumatic surface and the hydraulic surface of the rotary joint operate to cause the sealing rings to contact each other when hydraulic pressure exists in the joint due to the flow of coolant or more generally due to the flow of an incompressible fluid through the joint. The contacting seals form a mechanical face seal that allows coolant to flow from a non-rotating machine part to the rotating shaft of the spindle in a sealed manner. When the coolant flow is interrupted while the shaft is still rotating, for example between operations and / or when the rotation of the shaft is slowed, the pneumatic pressure applied from the outside to the rotary joint within the spindle creates a force tending to push the sealing rings away from each other, which creates an air gap between the rings which effectively avoids a dry-running condition of the sealing rings.

[0013] In one embodiment, the sealing device according to the present invention is configured to maintain the two sealing rings in contact with each other when pressurized coolant is present in the coolant passage. The pressurized coolant present in the coolant passage exerts a net liquid pressure on the slidable non-rotating seal carrier and the sealing element or ring to push the non-rotating seal carrier in a closing direction (i.e., toward the rotating seal ring). The net liquid pressure is greater than the net gas pressure exerted by pressurized air acting on the seal support externally in the opposite (opening) direction.

[0014] When the coolant flow is interrupted, the hydraulic force disappears and the seal rings separate to create an air gap to form between the two seal rings, so that excessive heating due to friction between the seal rings is avoided due to dry running. The seal carrier is moved by the aerodynamic force, which is no longer overcome by the hydraulic force. When the seal rings separate, air enters the coolant channel and clears any coolant that may remain therein.

[0015] Figure 1 and 2 A cross section through a portion of an air spindle 100 according to the invention is shown in two operating positions. Figure 1 In the illustration of FIG. 1 , the rotary joint 102 is shown in a closed or sealed position and in FIG. Figure 2, the rotary joint 102 is shown in a popped out or open position. The air spindle 100 may be an air spindle operated in a computer numerical control (CNC) machine that provides a source of pressurized air to power the spindle and also provides a source of liquid coolant for cooling and cleaning a tool (not shown) connected to the spindle in an area that cuts material from a workpiece (not shown) during operation.

[0016] The air spindle 100 includes a rotating portion and a non-rotating portion or mechanical component. Specifically, the non-rotating mechanical component 104 slidably and sealably accommodates a non-rotating seal carrier 106. The non-rotating seal carrier 106 includes a non-rotating seal ring 108 attached or otherwise formed thereon, which is slidably disposed within a bore 110 of the non-rotating mechanical component 104 together with the non-rotating seal carrier 106. In the illustrated embodiment, a mounting sleeve 112 forming a sliding bore 114 is mounted directly into the bore 110, and the non-rotating seal carrier 106 is slidably and sealably disposed therein.

[0017] The seal between the mounting sleeve 112 and the hole 110 and the seal between the sliding hole 114 and the non-rotating seal carrier 106 are respectively achieved by radial seals 116 and 118. As shown, the seal 116 is arranged between the components that are stationary relative to each other, while the seal 118 accommodates the sliding movement between the non-rotating seal carrier 106 and the sliding hole 114. The seals 118 and 116 are specifically embodied as O-rings, but other types of seals can also be used. Examples of other types of seals include lip seals, U-cup seals, etc.

[0018] In order to prevent the non-rotating seal carrier 106 from rotating relative to the non-rotating mechanical component 104, the non-rotating seal carrier 106 forms a groove 120 extending at least partially parallel to the longitudinal axis "L" of the main shaft 100. A pin 122 is connected to the wall of the sliding hole 114 and extends radially inward. The pin 122 cooperates with the groove 120 and is sized so that the groove 120 can slide axially along the pin 122, but cannot slide circumferentially, thereby preventing the relative rotation of the non-rotating seal carrier 106 without inhibiting its axial movement in the direction of the longitudinal axis L during operation.

[0019] The air main shaft 100 also includes a rotating component. In the partial cross-section shown in the figure, a portion of the air turbine shaft is shown. Specifically, the shaft 124 is rotatably supported by a bearing (not shown) and is arranged to rotate when compressed air is provided through an air inlet 126 and an air passage 128 formed in the non-rotating mechanical component 104. The air provided at the air inlet 126 will travel through the air passage 128 and pass through the axial turbine blades 128 connected to the shaft 124, thereby causing the blades and the shaft to rotate.

[0020] The shaft 124 includes an elongated body 130 and an enlarged diameter socket 132 on which a rotating seal ring 134 is co-rotatably mounted. A segmented coolant passage 136 is formed by a plurality of aligned holes and openings formed in various components of the machine. The coolant passage 136 extends from a coolant opening 138 formed in the non-rotating machine component 104 (which is also the opening of the bore 110) through an open end 140 of the sliding bore 114, through an inner bore 142 of the non-rotating seal carrier 106 having a generally tubular configuration, through a central opening of the rotating seal ring 134 and the non-rotating seal ring 108, and through a bore or barrel 144 extending through the elongated body 130 of the shaft 124.

[0021] When the air spindle is operating, air under pressure provided through the air inlet 126 is present externally relative to the non-rotating seal carrier. The various external surfaces of the non-rotating seal carrier 106 exposed to the pressurized air collectively provide a net aerodynamic surface upon which an aerodynamic force PF acts that is proportional to the air pressure provided at the inlet 126 for a particular configuration. Figure 4 A schematic diagram of the shape or distribution of the aerodynamic force PF approximating across the annular seal ring interface I is shown in FIG. Figure 4 As shown, for the air pressure P1 applied to the pipe joint from the outside and the internal pressure P0, the aerodynamic force PF has a parabolic distribution, which is represented by the shaded area under the curve in the graph. In the absence of other dynamic forces acting on the non-rotating seal carrier (i.e., excluding friction forces), the total externally applied aerodynamic force PF represented by the area under the curve applied to the interface I will tend to be in the direction toward the non-rotating mechanical component 104, that is, along Figure 1 and 2 , pushing the non-rotating seal carrier 106 to the left in the orientation shown in Figure 2 As shown by the arrow in Figure 2 As shown, the non-rotating seal carrier 106 along with the non-rotating seal ring 108 will move or retract deeper into the slide bore 114, resulting in a separation or gap 146 between the seal rings 108 and 134. The retraction of the non-rotating seal carrier 106 may cease when the pin 122 abuts the end of the slot 120, or more typically, when air pressure pushes the non-rotating seal carrier 106 and the non-rotating seal ring 108 away from the rotating seal ring 134.

[0022] When pressurized coolant is provided at coolant opening 138 , the various interior surfaces of non-rotating seal carrier 106 exposed to the pressurized coolant collectively provide a net hydraulic surface having a hydraulic force HF that, for a particular configuration, is proportional to the pressure of the coolant provided at inlet 138 . Figure 3Schematic diagrams approximating the shape or distribution of the hydraulic pressure PH across the annular seal ring interface I are shown in FIG. Figure 3 As shown, for a fluid pressure P1 applied internally to the pipe joint and an external pressure P0 (in this case, air pressure), the hydraulic force PH has a generally linear profile, which is represented by the shaded area below the graph. Note that while the graph shows a linear profile, the resultant force can be best represented by the curve when the magnitudes of the pneumatic and hydraulic profiles are closer to each other. In the illustrated embodiment, for example, the fluid pressure inside the joint can be several orders of magnitude greater than the air pressure applied externally to the joint, which results in Figure 3 The diagram of FIG. 1 shows a predominantly linear force distribution on interface I. However, a higher air pressure applied to the joint from the outside will tend to shape the collection curve more toward a parabolic shape.

[0023] The non-rotating seal carrier 106, together with the non-rotating seal ring 108 and the rotating seal ring 134, are configured so that the hydraulic pressure HF is greater than the pneumatic pressure PH of the working air and cooling hydraulic pressure selected for the machine. Thus, a net force equal to the difference between the hydraulic and pneumatic forces (HFPF) (excluding any static forces, such as friction) will tend to push the non-rotating seal carrier 106 in the direction of the shaft 124, i.e., toward Figure 1 and Figure 2 The non-rotating seal carrier 106 is pushed to the right in the direction shown in FIG. Figure 1 As shown, the non-rotating seal carrier 106 along with the non-rotating seal ring 108 will move outward or extend from the slide bore 114, causing the gap 146 to close and the seal rings 108 and 134 to sealingly engage one another.

[0024] Extension of the non-rotating seal carrier 106 may cease when the seal rings 108 and 134 contact in a manner that pushes or biases the non-rotating seal ring 108 into the rotating seal ring 134. This biasing forms a mechanical face seal at the interface between the seal rings 108 and 134 that maintains a seal around the coolant passage 136, which allows coolant to be transferred from the non-rotating machine component 104 under pressure into and through the bore 144 of the shaft 124 during operation. When the coolant supply ceases, the hydraulic pressure and corresponding force HF also ceases.

[0025] In the event that the air pressure continues to be present, and in the event that the hydraulic pressure HF is reduced to almost zero, the air force PF changes the direction of the net force acting on the non-rotating seal carrier 106 and causes the seal rings to separate, as described above. In this case, the air entering the coolant passage 136 also helps to clear any remaining coolant from the passage 136. Coolant escaping from the gap 146 can be collected and directed through the discharge opening 148 formed in the mounting sleeve 112, and also through the corresponding discharge opening 150 formed in the non-rotating machine component 104. Therefore, the opening and closing of the gap 146 can be selectively controlled by providing pressurized coolant inside the rotary joint 102 while the air pressure outside the joint 102 is present and the shaft 124 is rotating. In this way, coolant lubrication and cooling of the sealing interface created by the seal rings can be achieved when the seal rings are connected, and the separation of the seals can protect the seal rings under dry running conditions.

[0026] It should be understood that the structures described herein can be used in applications other than air turbine spindles, which are described herein as exemplary embodiments. In general, a rotary joint according to the present invention can be operated in any application in which an internal pressurization of the rotary joint by an incompressible fluid can be applied in the presence of an external pressurization of the rotary joint by a compressible fluid. In this case, the internal pressurization using the incompressible fluid will provide a net hydraulic pressure that tends to overcome the pneumatic force tending to push the sealing rings apart and close the seal between the sealing rings of the joint. When the application of the incompressible fluid is interrupted, the hydraulic force will decrease and will allow the pneumatic force applied to the joint from the outside by the compressible fluid to push the sealing rings apart. Therefore, the operating position of the sealing rings of the joint will depend on the pressure difference between the internal force provided by the pressure of the incompressible fluid and the external force provided by the pressure of the compressible fluid. This pressure difference sometimes produces a net opening or net closing effect on the sealing rings of the joint. It is contemplated that the balance ratio of the rotary joint according to the present invention can be greater than 50%, including greater than 100%, which balance ratio can be defined as the ratio of the net closing area of ​​the joint to the net opening hydraulic or pneumatic area.

[0027] Figure 5 A cross-sectional view of an alternative embodiment of an air spindle 200 is shown, in which the Figure 1 and 2The same or similar structures and features as the corresponding structures and features of the illustrated air spindle 100 are indicated by the same reference numerals used previously for simplicity. Thus, the air spindle 200 includes rotating and non-rotating portions or mechanical components. More specifically, the non-rotating mechanical component 104 slidably and sealably receives a non-rotating seal carrier 106. The non-rotating seal carrier 106 includes a non-rotating seal ring 108 attached or otherwise formed thereon, which is slidably disposed within a bore 110 of the non-rotating mechanical component 104 together with the non-rotating seal carrier 106. A mounting sleeve 212 forms a sliding bore 214 and is mounted directly into the bore 110. The sliding bore 214 is aligned with the sliding bore 114 ( Figure 1 ) is that a carrier flange 211 extending at least partially inwardly in a radial direction relative to a sliding hole 214 divides the hole into a first cylindrical cavity 202 and a second cylindrical cavity 204. The non-rotating seal carrier 106 is slidably and sealably disposed in the sliding hole 214.

[0028] In order to prevent the non-rotating seal carrier 106 from rotating relative to the non-rotating mechanical component 104, the non-rotating seal carrier 106 forms a groove 120 extending at least partially parallel to the longitudinal axis "L" of the main shaft 200. In this embodiment, a radial protrusion 222 formed in a locking nut 223 extends into and cooperates with the groove 120. The protrusion 222 is sized so that the groove 120 can slide along it but cannot slide circumferentially, thereby preventing relative rotation of the non-rotating seal carrier 106 without inhibiting its axial movement in the direction of the longitudinal axis L during operation.

[0029] The air spindle 200 also includes a closing spring 206. As shown, the spring 206 is an axial compression spring, but other arrangements may be used, such as a compression member made of more than one element, a body made of an elastic material such as rubber, etc. The spring 206 is used to apply a biasing force on the non-rotating seal carrier 106, which biasing force tends to push the non-rotating seal 108 in the closing direction, i.e., toward the rotating seal 134. The magnitude of the closing spring force can be constant or can be proportional or otherwise related to the axial position of the non-rotating seal carrier 106 within the sliding bore 214. The closing spring 206 is axially constrained or disposed between an annular surface 213 of the flange 211 facing the non-rotating seal ring 108 and a radially outwardly extending surface of the non-rotating seal carrier 106, which radially outwardly extends, for example, adjacent the outer periphery of the non-rotating seal 108.

[0030] When the air spindle is operated as described above, the air at the supplied pressure provides a net aerodynamic surface against which acts an aerodynamic force PF which, for a particular configuration, is proportional to the supplied air pressure. The spring force, together with the hydraulic force provided by the internal pressure, opposes the aerodynamic force to increase the total force tending to push the non-rotating seal carrier 106 in a direction toward the non-rotating mechanical component 104. This allows the seal to be maintained between the seal rings 108 and 134 so that the hydraulic pressure present in the joint 200 is lower than that in the air spindle or the joint 100, even in the absence of hydraulic pressure (depending, of course, on the constant selected for the spring 206 and the value of the applied air pressure). It is therefore contemplated that the balance ratio of the rotary joint 200 may be selected to be less than 50%.

[0031] All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference was individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0032] The terms "one" and "an" and "the" and "at least one" and similar indicators used in the context of describing the present invention (especially in the context of the following claims) should be interpreted as covering the singular and plural, unless otherwise indicated herein or clearly contradicted by the context. Unless otherwise indicated herein or clearly contradicted by the context, the use of the term "at least one" followed by a list of one or more items (e.g., "at least one of A and B") should be understood to refer to an item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B). The terms "including", "having", "including" and "containing" should be interpreted as open terms (i.e., meaning "including but not limited to"), unless otherwise indicated herein. Unless otherwise indicated herein, the description of the numerical range herein is intended only to be used as a shorthand method of individually referring to each individual value falling within the range, and each individual value is incorporated into the specification as if it were individually described herein. Unless otherwise indicated herein or clearly contradicted by the context, all methods described herein can be performed in any suitable order. Unless otherwise required, the use of any and all examples or exemplary language (e.g., "such as") provided herein is intended merely to better illustrate the invention and does not impose a limitation on the scope of the invention. No language in the specification should be construed as indicating any non-claimed element is essential to the practice of the invention.

[0033] Preferred embodiments of the present invention are described herein, including the best mode of implementing the present invention known to the inventor. After reading the foregoing description, variations of those preferred embodiments will be apparent to those of ordinary skill in the art. The inventor expects that the skilled person will appropriately adopt these variations, and the inventor intends that the present invention be implemented in a manner different from that specifically described herein. Therefore, the present invention includes all modifications and equivalents of the subject matter described in the appended claims as permitted by applicable law. In addition, the present invention includes any combination of the above-mentioned elements in all possible variations thereof, unless otherwise stated herein or clearly contradictory to the context.

Claims

1. A rotary joint, the rotary joint being arranged along an incompressible fluid path between a rotating mechanical component and a non-rotating mechanical component, comprising: a mounting sleeve disposed in a hole formed in the non-rotating mechanical component, the mounting sleeve forming a sliding hole; a non-rotating seal carrier slidably and sealingly disposed in the sliding bore, the non-rotating seal carrier comprising a non-rotating seal element, wherein the non-rotating seal element and the non-rotating seal carrier define an inner net hydraulic surface and an outer net pneumatic surface; A rotary sealing element, wherein the rotary sealing element is disposed on the rotary mechanical component; wherein the non-rotating seal carrier is movable in an axial direction between an extended position and a retracted position, wherein the rotating seal element and the non-rotating seal element are in contact to form a mechanical face seal, and wherein the rotating seal element and the non-rotating seal element are separated to form a gap in the axial direction; and wherein, during operation, contact of an incompressible fluid under pressure with the net hydraulic surface generates a closing force in a closing direction, the closing force tending to urge the non-rotating seal carrier from the retracted position toward the extended position; and wherein, during operation, a compressible fluid is adapted to be provided and present externally relative to the non-rotating seal carrier and around the mechanical face seal such that contact of the compressible fluid under pressure with the net aerodynamic surface generates an opening force in an opening direction, the opening force tending to urge the non-rotating seal carrier from the extended position toward the retracted position. 2 . The rotary joint of claim 1 , further comprising a spring disposed between the mounting sleeve and the non-rotating seal carrier, the spring being configured to provide a spring force in the closing direction.

3. The rotary joint according to claim 2, wherein: The mechanical face seal is formed when the total closing force existing in the closing direction is greater than the total opening force existing in the opening direction.

4. The rotary joint according to claim 3, wherein: The total closing force includes the spring force and the closing force generated by the incompressible fluid acting on the net hydraulic surface.

5. The rotary joint according to claim 3, wherein: The total closing force is provided primarily by the spring closing force, which is greater than the opening force generated by the compressible fluid acting on the net aerodynamic surface.

6. The rotary joint according to claim 1, wherein: The mechanical face seal is formed when the total closing force existing in the closing direction is greater than the total opening force existing in the opening direction.

7. The rotary joint according to claim 6, wherein: The total closing force is provided primarily by the incompressible fluid acting on the net hydraulic surface.

8. The rotary joint according to claim 6, wherein: The total opening force is provided primarily by the compressible fluid acting on the net aerodynamic surface.

9. The rotary joint according to claim 1, wherein: The compressible fluid is air, and wherein the incompressible fluid is a coolant.

10. A method for operating a rotary joint, comprising: providing a non-rotating seal carrier slidably and sealingly disposed within the sliding bore, the non-rotating seal carrier comprising a non-rotating seal element; defining a net hydraulic surface on an inner side of the non-rotating seal element and the non-rotating seal carrier; defining a net aerodynamic surface on an outer side of the non-rotating seal element and the non-rotating seal carrier; Providing a rotary sealing element disposed on a rotating machine component; as well as moving the non-rotating seal carrier in an axial direction between an extended position in which the rotating seal element contacts the non-rotating seal element to form a mechanical face seal and a retracted position in which the rotating seal element separates from the non-rotating seal element to form a gap in the axial direction; wherein movement from the retracted position to the extended position is accomplished by providing an incompressible fluid in contact with the net hydraulic surface to generate a closing force in a closing direction; and wherein movement from the extended position to the retracted position is accomplished by providing a compressible fluid external to and surrounding the mechanical face seal in contact with the net aerodynamic surface to generate an opening force in an opening direction.

11. The method of claim 10, further comprising providing a spring configured to provide a spring force in the closing direction.

12. The method according to claim 11, wherein: The mechanical face seal is formed when the total closing force existing in the closing direction is greater than the total opening force existing in the opening direction.

13. The method according to claim 12, wherein: The total closing force includes the spring force plus the closing force generated by the incompressible fluid acting on the net hydraulic surface.

14. The method according to claim 12, wherein: The total closing force is provided primarily by the spring closing force, which is greater than the opening force generated by the compressible fluid acting on the net aerodynamic surface.

15. The method according to claim 10, wherein: The mechanical face seal is formed when the total closing force existing in the closing direction is greater than the total opening force existing in the opening direction.

16. The method according to claim 15, wherein: The total closing force is provided primarily by the incompressible fluid acting on the net hydraulic surface.

17. The method according to claim 15, wherein: The total opening force is provided primarily by the compressible fluid acting on the net aerodynamic surface.

18. The method according to claim 10, wherein: The compressible fluid is air, and wherein the incompressible fluid is a coolant.

19. A rotary joint disposed along an incompressible fluid path between a rotating mechanical component and a non-rotating mechanical component, comprising: a mounting sleeve disposed in a hole formed in the non-rotating mechanical component, the mounting sleeve forming a sliding hole; a non-rotating seal carrier slidably and sealingly disposed in the sliding bore, the non-rotating seal carrier comprising a non-rotating seal element, wherein the non-rotating seal element and the non-rotating seal carrier define an inner net hydraulic surface and an outer net pneumatic surface; a rotary sealing element disposed on the rotating machine component; and a spring disposed between the mounting sleeve and the non-rotating seal carrier, the spring providing a spring force to the non-rotating seal carrier; wherein the non-rotating seal carrier is movable in an axial direction between an extended position and a retracted position, wherein the rotating seal element and the non-rotating seal element are in contact to form a mechanical face seal, and wherein the rotating seal element and the non-rotating seal element are separated to form a gap in the axial direction; and wherein, during operation, contact of an incompressible fluid under pressure with said net hydraulic surface and said spring generates a closing hydraulic force and a spring force in a closing direction that tend to urge said non-rotating seal carrier from said retracted position toward said extended position; and wherein, during operation, a compressible fluid is adapted to be provided and present externally relative to the non-rotating seal carrier and around the mechanical face seal such that contact of the compressible fluid under pressure with the net aerodynamic surface generates an opening force in an opening direction, the opening force tending to urge the non-rotating seal carrier from the extended position toward the retracted position.

20. The rotary joint according to claim 19, wherein: The mechanical face seal is formed when the total closing force existing in the closing direction is greater than the total opening force existing in the opening direction.

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