back-up valve的意思|示意

When installing the Series 4700, it is recommended that galvanized steel back up rings be used behind the valve flanges.

在安装系列4700夹管阀时，建议在阀门法兰后面采用镀锌钢支撑环加固。

PVC flocking materials used by high-frequency hot press molding, gas valve back up, with both gas permeability and gas leak-proof function.

用植绒PV C料经高频热压成型，倒阀门气嘴，具有双层防漏气渗气功能。