| 摘要 |
A piston type, pneumatically powered motor includes a valve assembly for reversibly supplying pneumatic fluid to opposite sides of a piston to reciprocate the piston through power strokes in both directions. The valve assembly has a spool reciprocably mounted in a sleeve that normally moves between two positions to reversibly supply pneumatic fluid to the piston. An actuating mechanism shifts the valve spool between its two normal positions responsive to movement of the piston near the end of each power stroke. When the reciprocation rate of the piston reaches a predetermined high or excessive rate, the actuating mechanism shifts the valve spool to a third position that short circuits the normal path of the pneumatic fluid flowing to the piston and channels the pneumatic fluid to an exhaust port.
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