For use withbackflowpreventer test cocks to protect from damage. 用于防回流阀测试旋塞,防止受到破坏. 互联网 They prevent steambackflowfrom the header to the boiler. 这种阀门能够防止蒸汽从集气箱倒流到锅炉里. 互联网 Thebackflowpreventer must be installed upstream of the regulator. ...