Fail Closed

Overview

Engineering reference data for Fail Closed in miscellaneous.

Key Formulas

Unit Conversion

$y = x \cdot k$

Multiply by conversion factor.

Linear Interpolation

$y = y_1 + \frac{(x - x_1)(y_2 - y_1)}{x_2 - x_1}$

Estimate between two known points.

Percentage

$p = \frac{\text{part}}{\text{whole}} \times 100\%$

Part as fraction of whole.

Variables

Understanding Fail-Closed Behavior

A control valve designated as Fail-Closed (FC) is engineered to move to its fully closed position upon loss of its operating signal. This is a critical safety feature in many process control systems.

The term "Fail" here refers to a loss of the control signal, not necessarily a mechanical failure of the valve itself. The closing action can be achieved through:

• Pneumatic signal loss: Typically using a spring-return actuator to drive the valve closed.
• Hydraulic signal loss: Using hydraulic accumulators or springs.
• Electric/electronic signal loss: De-energizing a motor or solenoid, often with a spring return.

Why it matters: Fail-closed valves are often used in systems where stopping flow is the safe default. For example, in a fuel supply line, a fail-closed valve will shut off fuel flow if the control system loses power, preventing potential hazards.

References

• Original Source