| 摘要 |
<p>The ventilators (2) in the building roof are operated by wires (5) moving round fixed pulleys (6) at one end, and suspended by hooks onto free pulleys (8) at the other end. Wires (9) lift and lower the free pulleys and are fixed at one end (10) to a fixed plate, and at the other end (11) to a moving plate (12). The operation of the moving plate is controlled by an endless chain mounted in a housing (13) the chain being toothed pinion driven by reduction gears from electric motor (21). The run of the moving plate is limited by cut-outs in both the high and low positions.</p> |
