Fuel pump for a direct injection system

A fuel pump (4) for a direct injection system provided with a common rail (3); the fuel pump (4) has: a pumping chamber (11); a piston (12) which is slidingly mounted inside the pumping chamber (11); a suction channel (14) connected to the pumping chamber (11) and regulated by a suction valve (15); an outlet channel (16) connected to the pumping chamber (11) and regulated by an outlet valve (17); an exhaust channel (27) which originates from the outlet channel (16) and is regulated by a pressure relief valve (28); and a setting device (19) which acts on the suction valve (15) to keep the suction valve (15) open during a pumping phase of the piston (12) and is provided with a hydraulic actuator (21) which is connected to the exhaust channel (27) to be driven by the fuel pressure present in the exhaust channel (27) itself.