Fire Safe - Secondary metal-to-metal seal ACTS as backup if primary seal is destroyed by fire.

防火安全-如果第一个密封被火烧坏，则第二个金属对金属密封作为后备密封发挥作用。

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The metal diaphragms act as the seal at the top of the valve. The primary improvement in this generation of valves is the elimination of the spring used to open the valve.

金属横膈膜在阀门的顶部作为密封。这一代阀门的主要的改进是取消了用于开启阀门的弹簧。

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BVI Business Company formation, all primary documents and corporate seal.

英属维尔京群岛商业公司的形成，所有主要文件和公司印章。

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Given the two red flags that had been thrown up previously, one would have expected that as a precaution a cement plug would have been placed somewhere in the wellbore as a secondary pressure seal before this primary pressure control system (heavy mud) was evacuated from the wellbore.

WSJ: The Oil Disaster Is About Human, Not System, Failure