| 摘要 |
<p>A double-acting piston-cylinder arrangement for actuating the door has an effective area on one side of the piston (15) at least three times greater than the effective area (20) on the other side. For opening of the door, pneumatic control valve (22) connects a pressure source (21) to both sides of the piston, whilst for closure and holding of the door, the pressure source (21) is connected to the said other side-of the piston. Rapid opening with a more gentle closing action is thereby provided. Preferably the smaller-area piston chamber is choked (25) during opening, the chamber acting as an air spring for gradual deceleration of the door. <IMAGE></p> |
