Double seals: Material code for the secondary seal is directly followed by the product seal face codes.

注： 双端面机械密封的型号表示方法为：在产品型号规格的后面书写两组材料代号，用横线相连。

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They are designed to provide a secondary seal in the event the cylinder valve develops leakage through the valve seat.

它们是设计用来在钢瓶阀门通过阀座产生泄漏的情况下提供一个二次密封。

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To study the influence of O-rings secondary seals, deformation behaviors of mechanical seal faces were analyzed under different pressures with the method of integral contact analysis by FEM.

采用整体接触有限单元法，考虑“O”型辅助密封圈的影响，计算了不同压力下机械密封端面变形行为。

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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