The action of compressed air (Fig. a), delivered through tube 6, shifts piston 1 to the right, overcoming the resistance of spring 5. This pushes balls 2 into conical space 3 which is limited by the surface of pusher 4. As pusher 4 moves upward it spreads shoes 7 (Fig. b), turning them about axis A. The pneumatic elements of the mechanism are shown in an enlarged scale.
$3761$SHP,Br$