A medical device delivery system includes a catheter defining an inner space, and an outer retractable portion positioned over the catheter and defining an annular space between the catheter and the outer retractable portion. At least one bypass opening through a sidewall of the catheter fluidly connects the inner space and the annular space. A tubular sealing member is positioned in the annular space proximal to the bypass opening. The tubular sealing member is movable between a compressed state in which proximal fluid flow through the annular space is inhibited by the tubular sealing member, and a non-compressed state in which proximal fluid flow through the annular space at the tubular sealing member is permitted.
