A pneumatic tool includes a shell defining first, second, third and fourth communicating spaces, a channel communicated with the second space, an inlet communicated with the channel, and an outlet communicated with the second space. A cylinder in the first space defines first, second and third ports. Pressurized air drives a rotor in the cylinder in a direction while entering the cylinder through the first port and leaving the cylinder through the third port and in an opposite direction while entering the cylinder through the second port and leaving the cylinder through the third port. A cover connected to the shell defines an aperture communicated with the second space, a first channel communicated with the third space on one hand and the first port on the other hand, a second channel communicated with the fourth space on one hand and the second port on the other hand. A rotational switch extends into the second space through the aperture and defines two cutouts. Different portions of the channel open to selective one of the cutouts as the rotational switch is rotated so that the rotor is driven at different speeds.