When compressed air is admitted into port 2 and ports 1 and 3 are connected to the atmosphere, the piston rod is set in its middle position. If compressed air is admitted through port 3 and ports 1 and 2 are connected to the atmosphere, pistons 5 and 6 move to the left and the rod is extended. If compressed air is admitted through port 1 and ports 2 and 3 are connected to the atmosphere, pistons 4 and 5 move to the right and the rod is retracted.
$3755$SHP,Dr$