Filling machine for filling containers with liquids, which comprises: - a rotary carousel provided with at least one tank for containing a liquid to be bottled; - a plurality of filling valve groups, each of which provided with: - a delivery duct in fluid communication with said containment tank for the flow of the liquid from said containment tank to a container to be filled with said liquid; said delivery duct being provided with a first conveyance portion fixed on the lower part to said containment tank, and a second conveyance portion (16") mechanically connected in fluid continuity with said first conveyance portion by means of removable fixing means and extended up to an outlet mouth for the liquid susceptible of being at least partially inserted in said container; - a return tube for the air return provided with at least one first section, placed to traverse said containment tank and extended up to an upper end thereof, and with at least one second section (14") placed coaxially within said delivery duct and extended up to a lower end thereof; - a first shutter placed to intercept said delivery duct and provided with a widened portion fixed to the second section (14") of said return tube and susceptible of interfering with a portion of said delivery duct in order to open and close said first shutter; - first actuator means mounted on said rotary carousel and mechanically connected to the upper end of the first section of said return tube in order to move it between a raised position, in which said first shutter is closed and a lowered position in which said first shutter is open; said filling machine being characterized in that said first and second sections (14', 14") of said return tube are made in a single body, the upper end of the first section of said return tube being removably connected to said first actuator means by means of quick coupling means. - a rotary carousel provided with at least one tank for containing a liquid to be bottled; - a plurality of filling valve groups, each of which provided with: - a delivery duct in fluid communication with said containment tank for the flow of the liquid from said containment tank to a container to be filled with said liquid; said delivery duct being provided with a first conveyance portion fixed on the lower part to said containment tank, and a second conveyance portion (16") mechanically connected in fluid continuity with said first conveyance portion by means of removable fixing means and extended up to an outlet mouth for the liquid susceptible of being at least partially inserted in said container; - a return tube for the air return provided with at least one first section, placed to traverse said containment tank and extended up to an upper end thereof, and with at least one second section (14") placed coaxially within said delivery duct and extended up to a lower end thereof; - a first shutter placed to intercept said delivery duct and provided with a widened portion fixed to the second section (14") of said return tube and susceptible of interfering with a portion of said delivery duct in order to open and close said first shutter; - first actuator means mounted on said rotary carousel and mechanically connected to the upper end of the first section of said return tube in order to move it between a raised position, in which said first shutter is closed and a lowered position in which said first shutter is open; - a delivery duct in fluid communication with said containment tank for the flow of the liquid from said containment tank to a container to be filled with said liquid; said delivery duct being provided with a first conveyance portion fixed on the lower part to said containment tank, and a second conveyance portion (16") mechanically connected in fluid continuity with said first conveyance portion by means of removable fixing means and extended up to an outlet mouth for the liquid susceptible of being at least partially inserted in said container; - a return tube for the air return provided with at least one first section, placed to traverse said containment tank and extended up to an upper end thereof, and with at least one second section (14") placed coaxially within said delivery duct and extended up to a lower end thereof; - a first shutter placed to intercept said delivery duct and provided with a widened portion fixed to the second section (14") of said return tube and susceptible of interfering with a portion of said delivery duct in order to open and close said first shutter; - first actuator means mounted on said rotary carousel and mechanically connected to the upper end of the first section of said return tube in order to move it between a raised position, in which said first shutter is closed and a lowered position in which said first shutter is open;