Since then we installed a backflow valve so it was less this time.
自从那时起，我们安装了一个逆流阀，所以这次少了很多。
The system should be flushed before the backflow valve is installed.
在安装回流阀之前系统应该进行冲刷。
Headstock piece on media flows and forces open or closed to prevent backflow valve media called a non-return valve.
启闭件靠介质流动和力量自行开启或关闭，以防止介质倒流的阀门叫止回阀。
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