roof drain的意思|示意

The emergency drainage device is an important device in floating roof tank, used to drain the overloaded water accumulated on the floating roof to ensure a safety for oil tank.

浮顶油罐紧急排水装置是浮顶油罐上的一个重要的附件，其主要作用是排出浮顶上的超载积水，保证油罐浮顶的使用安全。

Water came down from the roof through a small drain carved in the outside north wall of the grotto. It was led to a small pool which served to decant it before it flowed into the cistern proper.

水从屋顶沿著北边外墙挖的小水管流下来，形成一个小水池为协助它徐缓地流入更适合的贮水槽。

Roof rain runoff areas may require a drain or gravel sump to protect plants and structures.

屋顶雨水径流的地区可能需要排水渠或砾石坑保护植物和结构。