Air motor control

A runaway control for an air motor of the expansible chamber type comprising an air cylinder, a piston reciprocable therein, valve means shiftable alternately to effect supply of air to and venting of air from opposite sides of the piston to reciprocate the piston, said control being operable on increase in speed of the air motor above a speed limit to stop the motor and comprising

• pressure-responsive means comprising means defining an air chamber for air under pressure, means movable away from a first position in response to increase in air pressure in said chamber above a predetermined limit to a second position, and movable back to said first position on reduction of pressure in said chamber below said limit, said movable means widen in its first position enabling operation of the air motor and when in its second position cutting off the operation of the motor,
• said pressure-responsive means having a bleed for bleeding off pressure from the chamber at a controlled rate,
• an air pump controlled by the air motor,
• said pump being interconnected with the motor for operation simultaneously with the motor for delivering air under pressure at a rate related to the speed of the motor and having an outlet in communication with the chamber for the delivery of the air under pressure to the chamber,
• the pressure in the chamber being controlled by the rate of delivery of air under pressure to the chamber and the bleed of air from the chamber, whereby on increase in speed of the motor above said speed limit, the pump, operating at increased speed, delivers air under pressure at an increased rate to said chamber over and above the capability of the bleed to bleed off the increase, and on ensuing increase in air pressure in the chamber above said limit, said movable means moves to its said second position to cut off the motor.