Pneumatic unlocking and closing apparatus

Pneumatic unlocking and closing apparatus providing a movement having a soft braking phase at each end position, said apparatus comprising:

• a pneumatic piston-cylinder unit having a working chamber acting on a large piston area and a return chamber acting on a piston area which is reduced by an area of a piston rod, and a pressure actuation system which operates said unit, the pressure actuation system being formed as a substantially closed pressure system having
• a compressed air pump arranged to create both a relatively high working pressure in the working chamber and a less high counter pressure in the return chamber,
• a first plus pressure tank having a predetermined high pressure adapted to act as the working pressure in the working chamber thereby expelling the piston during the working stroke thereof, and
• a second minus pressure tank having a pressure which is less than the pressure of the plus tank, and into which the air of the working chamber is evacuated for returning the piston to its fully retracted position;
• and
• wherein the return chamber is connected to the working chamber
• via a pressure reduction valve giving the return chamber a certain predetermined pressure which is less than the working pressure in the working chamber when the piston is fully retracted,
• via a non-return valve which prevents unintentional evacuation of the pressure in the return chamber, and
• via an emergency release valve by which the pressure in the return chamber may be evacuated in an emergency.