| 摘要 |
A closure apparatus for a subsurface pit for servicing an aircraft located beneath an aircraft servicing surface across which aircraft travel is provided with an improved spring biasing arrangement. The system employs separate springs interposed between the hollow body of the pit and the lid so as to urge the pit lid from its horizontal seated position toward a fully raised position. Obstructions are provided for separately intercepting and disengaging the springs from acting against the pit lid as the pit lid is opened through intermediate angular positions between the horizontal seated position and the fully raised position. By sequentially isolating the pit lid from the action of each of the springs, one at a time, the moment of spring force opposing closure of the lid more closely follows the moment of the force of gravity tending to close the lid. This substantially reduces the maximum manual force that is thereby required to overcome gravity in opening the pit lid. The preload of each spring is preferably individually adjustable so as to allow the spring force to be fine tuned to closely match the force of gravity throughout the arcuate path of travel of the pit lid.
|
