... closed interva Quickly-being closed interval (0°-15°) A little fast,competely being closed interval 4.Features 1, technical performance: reliable ... , simplicity, flexibility, easy operation.2) no harm to the door, frame, wall and other home structure4 high safety factor usage ... large pressure.2) due to the shock absorbing, make the door and door frame not destroyed ,meanwhile prolong the working life 5 ...