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In the BOP stack they are<br />
always positioned in such<br />
way, that annular preventer<br />
is the working preventer<br />
positioned on the top of the<br />
stack, and ram preventer is<br />
on the bottom as the<br />
backup.<br />
Working preventer is always<br />
positioned far from the<br />
source of danger, to be in<br />
position to change it if fails.
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