Copper tubing shall not be used on the downstream side of the backflow preventer.
在防回流阀的下游不应该安装铜管。
Second check must be drip tight when pressure is applied to downstream side of valve.
当阀门下游一侧出现压力时，第二止回阀必须是无滴漏。
Simultaneously, some rather instable rock masses were formed in some parts of the upstream and downstream side-walls of the main machine hall.
同时，在厂房上下游边墙的局部地段形成比较严重的不稳定岩体。
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