A system for treating a vascular condition comprises a catheter having at least one lumen, a stem received within a distal portion of the lumen, a sealing member positioned on the stem, and a balloon operably attached to a distal portion of the catheter. The stem includes a proximal body portion, a sealing portion, and a shoulder portion. The sealing member is movable with hydrodynamic force from an initial air-release position on the proximal body portion of the stem to a sealed position on the sealing portion of the stem. A method for purging a balloon catheter prior to use comprises injecting a liquid into a proximal end of a balloon catheter lumen. The injected liquid forces air through a gap between the lumen wall and a sealing member. The liquid then contacts the sealing member and repositions it to a sealed position.