NC — Normally closed

01

NC: definition and engineering context

Normally closed. Flow path is closed in the defined normal or de-energized condition.

The term belongs to the valves & circuits context. Its exact limits can depend on the cited standard, catalog convention, unit system, reference state, and component configuration.

02

Why NC affects pneumatic selection

Confirm which ports the catalog calls normally closed.

• NO: Use when the required fail-state needs flow.
• Pilot operated: Check minimum pilot or differential pressure.
• Direct acting: Useful where zero differential operation matters, usually with lower maximum flow.
• Spool: Leakage, overlap, and contamination tolerance affect application behavior.

03

How to evaluate NC in a catalog or replacement project

Read the value together with its unit, test basis, operating pressure, temperature, circuit state, and manufacturer definition.

For replacement work, compare the complete datasheet and drawing. A matching abbreviation or nominal size does not by itself prove functional or dimensional interchangeability.

• Normally open: Flow path is open in the defined normal or de-energized condition.
• Pilot-actuated valve: Main element is shifted using pilot pressure.
• Direct-actuated valve: Solenoid or mechanical input acts directly on the sealing element.
• Sliding valve element: Internal element routes air between valve ports by moving along a bore.