Piston actuated rotary union

1. A rotary union, comprising:

a housing having a bore in fluid communication with a media channel opening and a piston bore having an open end disposed at a radially offset distance with respect to the bore, the piston bore being fluidly isolated from the media channel opening and the bore, and is fluidly connected to an actuation port;

a non-rotating seal carrier slidably disposed within the bore in the housing and having a media channel in fluid communication with the bore;

an actuation arm connected to the non-rotating seal carrier and extending radially outwardly therefrom with respect to the bore, the actuation arm at least partially overlapping the open end of the piston bore;

a piston slidably disposed within the piston bore and being unattached from the housing and actuation arm such that the piston can freely move axially within the piston bore independently from the housing and the non-rotating seal carrier during operation to define a variable piston volume between the piston and the piston bore, the variable piston volume being fluidly connected to the actuation port, the piston being adapted to extend out from the open end of the bore when a fluid pressure provided via the actuation port is present in the variable piston volume, the piston having an axially-outward face that contacts the actuation arm and being configured to releasably abut the actuation arm and to urge the actuation arm, and thus the non-rotating seal carrier, to displace relative to the bore when the piston displaces relative to the piston bore; and

a seal disposed around the non-rotating seal carrier and disposed to create a sliding seal between the non-rotating seal carrier and the bore;

wherein the non-rotating seal carrier is arranged to extend relative to the housing when the fluid pressure is present in the piston bore.

2. The rotary union of claim 1 , further comprising a collection channel formed in the housing around the bore and in fluid communication with the bore, the collection channel disposed between the seal and an open end of the bore opposite the media channel opening, the collection channel extending annularly around an entire cross section of the bore and adapted to collect a media fluid leakage past the seal.

3. The rotary union of claim 2 , further comprising at least one vent passage that is formed in the housing and extending from the collection channel entirely through the housing to an outer portion of the housing, the at least one vent passage being adapted to vent fluid present or collected within the collection channel out of the housing.

4. The rotary union of claim 1 , further comprising a mechanical stop that limits a displacement of the non-rotating seal carrier with respect to the housing in an extending direction.

5. The rotary union of claim 4 , wherein displacement of the non-rotating seal carrier is limited such that the piston remains slidably supported within the piston bore.

6. The rotary union of claim 4 , wherein the mechanical stop includes a snap ring installed in a groove formed in the housing around a free end of the non-rotating seal carrier, the snap ring abutting the actuation arm when the non-rotating seal carrier is extended relative to the housing.

7. The rotary union of claim 1 , wherein the bore is generally cylindrical and forms a gap between an inner diameter of the bore and an outer diameter of the non-rotating seal carrier, the gap being configured to allow for angular misalignment in an axial direction between the non-rotating seal carrier and the bore, which advantageously permits the rotary union to accommodate assembly and operational misalignment conditions between rotating and non-rotating machine components.

8. The rotary union of claim 7 , wherein the non-rotating seal carrier and the bore, are slidably associated along a cylindrical land surface having an axial length along the bore, the axial length and inner diameter dimension of the cylindrical land surface being configured to accommodate misalignment between the non-rotating seal carrier and the bore.

9. The rotary union of claim 1 , wherein the piston is a floating piston having a clearance fit with the piston bore such that a leakage of actuating fluid provided to the piston bore is present during operation.

10. The rotary union of claim 1 , wherein a clearance between the piston and the piston bore is configured to permit at least some leakage of fluid from within the piston bore at times when the fluid pressure is present at the actuation port and the variable piston volume.

11. The rotary piston of claim 10 , wherein when the fluid pressure is present in the variable piston volume, the fluid pressure is arranged to impart a pneumatic force on a back side of the piston that is exposed to the variable piston volume.