工作原理：当管道和水箱内部形成真空时，大气压便会顶开阀盖，大气进入系统内部，平衡系统压力，消除真空影响。

Working principle: when the internal piping and tank vacuum, atmospheric pressure will be the valve cover, air enters the system, balance the system pressure, eliminate the effect of vacuum.

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某些制造厂商反对在发动机处于热态以及冷却系内压力依然较高时打开水箱盖。

Some manufacturers warn against taking off the cap when the engine is hot and pressure in the cooling system is high.

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