英语翻译Over the past four years,PPV has been proven effective f

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英语翻译
Over the past four years,PPV has been proven effective for ventilation of highway tunnels,railway tunnels,and subway tunnels.The techniques of PPV are applied with the use of a large diameter (1200-1800mm,truck-mounted blower called a Mobile Ventilation Unit (MVU).Because the MVU is located outside of the tunnel during ventilation operations,it is not subjected to the extreme conditions that exist inside a tunnel during a fire.If a fixed system happens to fail due to prolonged exposure to extreme heat,the MVU is still capable of providing effective ventilation.

在过去的四年间,PPV被证实无论是对高速公路,铁路还是地铁的隧道通风都很有效.与PPV这项技术同时应用的还有更大直径的通风设施的应用（直径1200－1800毫米,被称作移动通风机的安装在卡车上的通风机）.由于在通风设备工作时,移动通风机位于隧道的外部,它不会受制于大火中隧道内极端的条件.如果安装好的系统碰巧由于暴露在极端的环境下失灵了,移动通风机仍然可以提供有效的通风.

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