Rotary union with selectively controlled seal

1. A rotary union, comprising:

a housing having a bore in fluid communication with a media channel opening and a control chamber disposed around the bore and being fluidly isolated from the media channel opening;

a non-rotating seal member slidably disposed within the bore in the housing and having a media channel that is fluidly open to the media channel opening through the bore;

a first sliding seal disposed around the non-rotating seal member and disposed to seal the control chamber from the atmosphere;

two additional sliding seals disposed around the non-rotating seal member adjacent one another, the two additional seals disposed between the control chamber and the media channel opening as a pair to seal the control chamber from the media channel;

wherein the non-rotating seal member is arranged and configured to extend relative to the housing when a fluid under pressure is present in the control chamber such that the non-rotating seal member engages a rotating seal member and forms a mechanical face seal therewith while the rotating seal member is rotating.

2. The rotary union of claim 1 , wherein the non-rotating seal member has a first balance ratio arranged to urge the non-rotating seal member to extend from the housing when the fluid under pressure is present at the media channel opening.

3. The rotary union in claim 1 , wherein the non-rotating seal member has a second balance ratio arranged to urge the non-rotating seal member to extend from the housing when the fluid pressure is present at the control chamber and at least one of an ambient pressure or a vacuum is present at the media channel.

4. The rotary union of claim 1 , further comprising a control chamber inlet and a control chamber annulus fluidly interconnecting the control chamber inlet and the control channel when the housing is connected to a non-rotating machine component.

5. The rotary union of claim 1 , further comprising an opening spring disposed to provide an opening force urging the non-rotating seal member to retract into the housing.

6. The rotary union of claim 1 , further comprising a non-rotating machine component forming a receiving counterbore into which the housing is disposed.

7. The rotary union of claim 1 , further comprising a first fluid valve arrangement operable to selectively fluidly connect the control chamber with at least one of a source of pressurized incompressible media, a vacuum sink, and a vent.

8. The rotary union of claim 7 , further comprising a second fluid valve operable to selectively fluidly connect the media channel with at least one of a source of pressurized compressible media, the source of pressurized incompressible media, the control chamber, the vacuum sink, and the vent.

9. The rotary union of claim 1 , further comprising a rotating seal member disposed on a rotating machine component such that the rotating seal member engages the non-rotating seal member when the non-rotating seal member is sufficiently extended from the housing.

10. The rotary union of claim 9 , further comprising a non-rotating seal ring disposed at an end of the non-rotating seal member, and a rotating seal ring disposed on the rotating seal member in facing relationship with the non-rotating seal ring, such that engagement of the rotating seal ring with the non-rotating seal ring provides a mechanical face seal along a media channel, the media channel being in fluid communication with the media channel opening and extending through portions of the rotating machine component and the housing.

11. A system for selectively fluidly interconnecting a media channel defined through portions of rotating and non-rotating machine components, comprising:

a receiving counterbore defined in the non-rotating machine component, a media channel opening in fluid communication with the receiving counterbore, and a control channel;

a housing disposed within the receiving counterbore and having a bore in fluid communication with the receiving counterbore and a control chamber in fluid communication with the control channel;

a non-rotating seal member slidably and sealingly disposed within the bore in the housing and having a media channel that is fluidly open to the media channel opening through the receiving counterbore;

a first sliding seal disposed around the non-rotating seal member and disposed to seal the control chamber from the atmosphere;

two additional sliding seals disposed around the non-rotating seal member between the control chamber and adjacent one another, the two additional seals disposed as a pair to seal the control chamber from the media channel; and

a first fluid valve arrangement operable to selectively fluidly connect the control chamber with at least one of a source of pressurized incompressible media, a vacuum sink, and a vent, such that the non-rotating seal member is arranged and configured to extend relative to the housing when a fluid under pressure is present in the control chamber such that the non-rotating seal member engages a rotating seal member and forms a mechanical face seal therewith while the rotating seal member is rotating.

12. The system of claim 11 , further comprising a second fluid valve operable to selectively fluidly connect the media channel with at least one of a source of pressurized compressible media, the source of pressurized incompressible media, the control chamber, the vacuum sink, and the vent.

13. The system of claim 11 , further comprising an opening spring disposed to provide an opening force urging the non-rotating seal member in a retracting direction relative to the housing.

14. The system of claim 11 , further comprising a rotating seal member disposed on the rotating machine component such that the rotating seal member engages the non-rotating seal member when the non-rotating seal member is sufficiently extended relative to the housing.

15. The system of claim 14 , further comprising a non-rotating seal ring disposed at an end of the non-rotating seal member, and a rotating seal ring disposed on the rotating seal member in facing relationship with the non-rotating seal ring, such that engagement of the rotating seal ring with the non-rotating seal ring provides a mechanical face seal along the media channel.

16. A method for operating a rotary union adapted to provide a mechanical face seal along a media channel extending between a rotating machine component and a non-rotating machine component, the method comprising selectively engaging the mechanical face seal by applying a fluid pressure to a control chamber that is fluidly isolated from the media channel and that is defined between a non-rotating seal member and the non-rotating machine component;

wherein the non-rotating seal member is slidably disposed within a bore in the housing and includes a portion of the media channel, said media channel being fluidly open with a media channel opening through the bore; and

wherein the fluid pressure applied urges the non-rotating seal member to extend relative to the housing such that the non-rotating seal member engages a rotating seal member and form the mechanical face seal therewith while the rotating seal member is rotating.

17. The method of claim 16 , further comprising maintaining the mechanical face seal in an engaged position during fluid evacuation from the media channel.

18. The method of claim 16 , further comprising providing a first net hydraulic force on the non-rotating seal member as a result of fluid pressure in the control chamber acting on a first balance ratio structurally defined on the non-rotating seal member.

19. The method of claim 18 , further comprising providing a second net hydraulic force on the non-rotating seal member as a result of fluid pressure in the media channel acting on a second balance ratio structurally defined on the non-rotating seal member.