Abstract: A piston pump for pumping fuel in which a risk of fuel getting into the area of a shaft seal is limited. The fuel pump includes a separation chamber which is provided between a shaft seal and a fuel chamber that contains fuel. Located in the separation chamber is for instance air as a separator means, and the separation chamber communicates with an air inlet of the engine. This assures that fuel cannot get into the area of the shaft seal or escape to the outside. The fuel pump is suitable in particular for internal combustion engines in which the fuel must be delivered at high pressure.