SME
Process Dynamics & Control · Problem type
Fail-open or fail-closed valves
Use this for “Should the steam valve to a reboiler fail open or fail closed if the instrument air is lost?”
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If the air fails, which way should this valve go?
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Assumptions
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The valve moves on instrument air; when the air fails, its spring drives it to the safe end.
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Air to open fails closed; air to close fails open.
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Safe means the plant moves toward cool, empty and stopped, not toward a runaway.
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