The invention relates to a device for pumping a liquid in a liquid line, in particular in a bottling system. The object of the invention is a device for pumping a liquid in a liquid line, the liquid-guiding areas of which device can be cleaned and/or disinfected without disassembling the piston assembly or performing any other interventions from the exterior. 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 disposed 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 inventive 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) acts. Also, the chamber (7) is connected to the liquid line (1) by means of an elastic liquid-impermeable element (8), which element can be deformed under the pressure exerted by the volume of the secondary liquid displaced by the pump piston (6).