An occlusion device for sealing a puncture through tissue includes a tubular wire member having a proximal end, a distal end sized for insertion into the puncture, a lumen extending between the proximal and distal ends, a port adjacent the proximal end communicating with the lumen, and a balloon on the distal end. A source of fluid is connectable to the wire member for delivering fluid via the port into the lumen for expanding the balloon. A piston is movable axially within the wire member to allow fluid to be delivered into the lumen, to isolate the lumen, and to deliver fluid within the lumen into the balloon to expand the balloon.