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 piston for free axial movement within the piston bore such that a variable piston volume is defined between the piston and 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 piston relative to the piston bore;
• pushing the actuation arm with the piston and urging 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.