Abstract: A sound absorber for intermittent exhaust gas, particularly for use in connection with a compressed air operated motor employed, for example, in a hand grinder. The sound absorber is arranged predominantly in the housing of the motor and includes an exhaust air discharging channel having an alternately varying cross-section to define a succession of continuously alternating narrow and wide passages for changing continuously the direction of flow of the exhaust air about an angle that is always lower than 90.degree. with respect to the axis of the discharge channel so that the ratio of successive minimum and maximum cross-sections of the channel is at most 4:1. The discharge channel is terminated with a nozzle plate defining a plurality of outlet nozzles the central axes of which converge in the direction of flow.

Abstract: A pneumatic hand tool comprises a housing having a compressed-gas inlet and provided with a pneumatically powered motor which carries on one side a tool holder such as a chuck and on the other side a governor. A speed-control valve is operated by the governor and can close a first air passage between the inlet and the motor to maintain the motor speed below a predetermined limit. Another passage is provided which bypasses the governor-controlled speed-control valve and a valve is provided in this bypass conduit which is openable in order to allow the hand tool to operate at a speed substantially above the governor-established speed.