常见例句双语例句The backflow preventer must be installed upstream of the regulator.防倒流装置必须安装在调节阀的上游位置。The relief valve may be serviced while on or off the backflow preventer valve.可以在防回流阀上维修安全阀,或将其从防回流阀拆卸下来维修。 返回 backflow preventer