常見例句雙語例句The backflow preventer must be installed upstream of the regulator.防倒流裝置必須安裝在調節(jié)閥的上游位置。The relief valve may be serviced while on or off the backflow preventer valve.可以在防回流閥上維修安全閥,或將其從防回流閥拆卸下來維修。 返回 backflow preventer