Abstract: Pneumatic system for controlling the valves, of an internal combustion engine; the pneumatic system is provided with: a pneumatic accumulator containing pressurized air; a pneumatic manifold; a control device to connect the pneumatic manifold alternatively to the pneumatic accumulator with the internal combustion engine in the high rpm range and to the atmosphere with the internal combustion engine in the low rpm range; a plurality of pneumatic springs, each of which has a variable volume actuating chamber and a piston mounted slidingly inside the actuating chamber; a plurality of connecting conduits, each of which connects the actuating chamber of a respective pneumatic spring to the pneumatic manifold; and a plurality of calibrated cross-sectional portions, each of which has a reduced cross-sectional area and is arranged along a respective connecting conduit.