An apparatus for sealing a vascular puncture and for properly locating and deploying a sealing member. The apparatus comprises a lumen which extends from an opening in the distal region of the apparatus to another opening in the proximal region of the apparatus. A sealing member is located at the end of the lumen. When the distal opening is positioned within the blood vessel lumen, blood flows through the distal opening, through the lumen and out of the proximal opening indicating that the sealing member is within the blood vessel lumen. When the sealing member is withdrawn from the vessel lumen, it blocks the blood flow into the distal opening. The sealing member may be further withdrawn a predetermined distance so that no part of the sealing member extends into the blood vessel lumen. The sealing device is then detached from the delivery apparatus to seal the vascular puncture.
