The invention concerns a pump having a housing; a working chamber located in the housing for delivery of a fluid; a suction channel which is in flow connection with the working chamber for guiding the fluid into the working chamber; a valve unit disposed in the suction channel, the valve unit has a guide body, a limiting element which is guided for displacement in the guide body and has at least one displacement stop for limitation of displacement, a valve which is movable between an open position and a sealing position for controlling the flow of the fluid into the suction channel, wherein the valve is guided for displacement, and a pressure element which presses the limiting element in the direction of the sealing position of the valve; as well as a pressure channel which is in flow connection with the working chamber for guiding the fluid out of the working chamber.