Piston actuated rotary union

A method for operating a rotary union, comprising:

• providing 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 fluidly connected to an actuation port;
• slidably disposing a non-rotating seal carrier within the bore in the housing, and fluidly connecting a media channel with the bore;
• providing 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;
• slidably disposing a cylindrical piston within the piston bore such that a variable piston volume is defined between the cylindrical piston and the piston bore, the piston being unattached from the housing and the actuation arm such that the piston can freely move axially within the piston bore independently from the housing and the non-rotating seal carrier, the piston being adapted to extend out from the open end of the piston bore;
• applying an actuation fluid pressure at the actuation port such that the actuation fluid pressure is present in the variable piston volume and providing a pneumatic force tending to extend the cylindrical piston relative to the piston bore;
• pushing the actuation arm by detachably urging an axially outward face of the piston into contact with and releasably abut the actuation arm and urging the actuation arm, and thus the non-rotating seal carrier, to displace relative to the bore when the cylindrical piston displaces relative to the piston bore.