No matter how the valve is installed, the back of the upstream seat protects the face of the downstream seat.

无论阀门如何安装，上游阀座的后背都能够保护下游阀座的表面。

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Ships now dock at Wushan, where passengers board 20-seat launches for a six-hour upstream voyage on the Daning River through the Longmen, Bawu, and Dizui gorges.

船现在停靠在巫山，在那里旅客登上20座的小艇在大宁河上做6个小时的逆流航行，经过龙门峡、巴巫峡和笛嘴峡。

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While medium pressure and the upstream end of the resilient and flexible structures to increase the downstream end of the valve seat seal.

同时介质压力与上游端挠性结构的回弹力又增加了下游端阀座的密封。

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