The device should not be installed inside a wall or in a concealed location. Copper tubing shall not be used on the downstream side of the backflow preventer.是什么意思_The device should not be installed inside a wall or in a concealed location. Copper tubing shall not be used on the downstream side of the backflow preventer.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句