It is a protective device composed with the emergency governer for protecting overspeed.  When the flying hammer flies , it hits and removes the hook at end of the throttle and the throttle sliding valve lines out under the function of spring force to cut the high-pressure oil to the main steam valve manipulating pedestal and servomotor of extraction check valve, so that the main steam valve and extraction check valve are quickly closed. In the mean time the high-pressure oil enters to the lower part of the staggered oil valve to make the steam control valve close quickly. This throttle can be stopped manually too. Only the rotation speed decreases to 3000r/min, can the throttle be reset, and the throttle can not be reset when the rotating speed is higher than 3000r/min, in order to avoid damage of flying hammer and hook.