Nomally Closed

Overview

Engineering reference data for Nomally 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

Normally Closed vs. Fail-Closed

It is critical to distinguish between the static physical state of a valve or damper and its dynamic behavior upon loss of control signal.

• Normally Closed (NC): This is a physical configuration. The valve or damper is mechanically biased or constructed to be in the closed position. An operator must actively open it for normal operation. It is a description of its resting or default state when not powered or actuated.
• Fail-Closed (FC): This is a control strategy. It describes the required action of a valve or damper when its control signal (e.g., power, air pressure) is lost. A control valve designed to close on signal failure is labeled Fail-Closed (FC).

Control Signal Types

The control signal actuating a valve can be from various sources, which influences its failure mode:

• Pneumatic: Uses air pressure.
• Hydraulic: Uses hydraulic fluid pressure.
• Electric: Uses electrical power (e.g., motorized actuator).

References

• Original Source