The present invention describes a pumping device (1) for pumping fluids. The pumping device (1) comprises a force transmitting element (2), a tension unit (3) coupled to the force transmitting element (2) and a seal element (10). The force transmitting element (2) is adapted for transferring an upstroke and a downstroke to a pump plunger (5) for pumping fluid (12). The tension unit (3) is adapted for applying a tension force (F) to the force transmitting element (2) for keeping the force transmitting element (2) under tension during the upstroke and the downstroke. The seal element (10) is adapted for sealingly preventing pumping fluids (12) during the downstroke and for enabling pumping fluid (12) during the upstroke. A part (16) of the seal element (10) is rigidly coupled with the force transmitting element (2).