A wireline pressure control string for use in performing wireline operations on a hydrocarbon well is disclosed. The wireline pressure control string includes a pumpdown assembly having a pumpdown sub and at least one pumpdown valve. The pumpdown sub includes a body and a through bore which extends axially through the body and is fluidly connectable to the well bore. The pumpdown valve includes an inlet which is fluidly connectable to a pumpdown fluid source and an outlet which is fluidly connected to the through bore. The wireline pressure control string may also include a connector positioned below the pumpdown assembly for releasably securing the wireline pressure control string to the wellhead assembly. In certain embodiments, the pumpdown valve may be connected to the pumpdown fluid source with a flexible flowline.