As piston 1 travels downward in cylinder 2, a braking effect is obtained and air is drawn through the clearance between the wall of cylinder 2 and the piston into the upper end of the cylinder. But when piston 1 travels upward, air flows out both through the clearance and through ball-type check valve 3 which is opened by the air. This sharply reduces the braking effect.
$3638$SHP,DC$