Ball and disc over-speed shut-off mechanism for a rotary pneumatic tool

A rotary pneumatic tool comprising:

• a motor having a rotor mounted for rotation about an axis within a stator;
• an input opening for connection of the tool to a source of compressed gas;
• a plurality of walls defining passageways within the tool between the input opening and the rotor;
• a frusto-conical bistable spring washer coaxially mounted with the rotor and having an outer circular edge;
• the spring washer being shiftable between two stable configurations:
• a frusto-conical non-sealing configuration, and an inverted frusto-conical sealing configuration;
• the outer circular edge of the spring washer sealingly contacting one of the walls defining the passageways when the spring washer is in the stable sealing configuration, such that communication through the passageways between the source of compressed gas and the rotor is interrupted when the spring washer is in the stable sealing configuration;
• a body coaxially mounted for rotation with the rotor;
• and
• flyweight means mounted movably in the body for imparting a force upon the spring washer, said force being progressively increased with higher speeds of rotation of the rotor and upon attaining a predetermined amount forcing said washer from the stable nonsealing configuration to the stable sealing configuration for deactivating said tool.