A slide flow distributor to direct and modulate a gaseous fluid, in inlet and outlet. This regulation is carried out by means of a spool, which conveys compressed air in a determined charging direction and puts in communication the other chamber with the environment at the same time. This is a servo-actuator which can be used in the field of pneumatic systems of valve actuation. It has a specific pneumatic servo-actuating system using compressed air. This distributor uses a linear motor using a new pneumatic servo-actuator which generates a force in the same direction of the axial force of the motor, with the result that the spool is accelerated in a predetermined direction. The pneumatic servo-actuator is made of a profiled body, a plurality of balls and corresponding elastic means which press the plurality of balls on the side surface of the profiled body.