An apparatus for sealing a puncture through tissue includes an elongate member having a lumen extending between proximal and distal ends thereof, and a balloon carried on the distal end. In one embodiment, a housing on the proximal end includes an interior communicating with the lumen, and a valve assembly, e.g., with a one-way valve allowing access into the interior upon applying a pressure differential across the valve, and a plunger for overriding and opening the valve. In another embodiment, a port adjacent the proximal end communicates with the lumen, and a fluid source is connectable to the elongate member for delivering fluid via the port into the lumen for expanding the balloon. A piston is movable axially within the elongate member to deliver fluid into the lumen, to isolate the lumen, and/or to deliver fluid within the lumen into the balloon to expand the balloon.
