As piston 1 is moved to the right by the action of compressed air, rod 2 of the piston, actuates rod 3 of the hydraulic booster, moving piston 4 to the right. As piston 4 moves in cylinder 5, compressing the hydraulic fluid in the cylinder, it develops the required pressure in the hydraulic circuit connected to port a. Spring 6 returns pistons 4 and 1 to the initial position.
$4214$CHP,Dr$