下泄背压控制阀维持下泄流上游段或下泄热交换器处的压力，防止压力过低引起流体汽化。
The letdown back-pressure regulating valve maintains pressure in the section of letdown upstream or the letdown heat exchanger to prevent the letdown liquid flashing to steam.
但事实证明，这个椭圆形标记着一条长河的上游段，当他放大镜头后，他发现那些矩形是隐藏的构造。
But it turned out the oval marked the former course of a long-gone river, and when he zoomed in, he found the rectangles were buried structures.
最后对植物坝前上游段推移质泥沙的输移特性进行了研究，初步探明了植物“柔性坝”的固沙机理。
Lastly, studies transportation characteristic of bed load sediment of upstream end before vegetation dam. Preliminarily clear sand-binding mechanism of vegetation "flexible dam".
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