An overspeed control means for pneumatic tools which includes a split ring
valve slidably arranged in a circumferential groove formed in a cage
member affixed to the rotor shaft of the tool. When the cage member
exceeds a predetermined rotational speed, the ring valve will expand and
be moved, by pressure differential acting thereupon, into engagement with
a valve seat to block holes in a flow circuit for pneumatic medium being
conducted to the rotor of the tool, whereby tool operation is terminated.
