The invention relates to a pump for a liquid product dispenser, which includes a reservoir and interacts with a manually actuatable element provided with an injection orifice. The pump includes a body embodied in the form of a single piece and including a seat which covers the reservoir and is provided with an intake orifice and a flap, which is mounted on the seat by a joint associated with an elastic bellows which enables the flap to be reversibly tilted towards the seat, by pressing on the actuating element, in such way that the injection orifice is opened and the intake orifice is simultaneously closed.