The invention relates to a device for pumping a liquid in a liquid line, in particular into a bottling system. The aim of the invention is to provide a device for pumping a liquid in a liquid line, and the liquid-guiding areas thereof can be cleaned and/or disinfected from the outside without disassembling the piston or carrying out other operations in the arrangement. According to the invention, a device for pumping a liquid in a liquid line (1) comprises a pump element (2) and two valves (3, 4) which are arranged in the liquid line upstream of and downstream from the pump element, said pump element (2) comprising a pump piston (6) operating in a cylinder (5). The claimed device is characterized in that said pump element (2) comprises a closed chamber (7) having a constant volume of a secondary liquid on which the pump piston (6) works. Also, the chamber (7) is connected to the fluid line (1) by means of an elastic liquid-permeable element (8), said element can be deformed under pressure exerted by the volume of the secondary liquid displaced by the pump piston (6).