Normally closed valve symbol
Also called NC valve, Locked closed valve
A normally closed valve is shut during normal operation and only opened for start-up, maintenance or emergencies. Showing it closed matters for every isolation and line-up.
What the normally closed valve symbol means
A normally closed valve is shut during normal operation and only opened for start-up, maintenance or emergencies. Showing it closed matters for every isolation and line-up.
How it is drawn
A valve body drawn filled solid black, usually with NC beside it. Locked closed valves are marked LC, and car-sealed closed valves CSC.
Variants
- NO: normally open
- LO: locked open
- CSO: car-sealed open
The normally closed valve symbol in each standard
Drawn as on most US-style legend sheets.
ISO 10628-2 has no separate symbol for this. Check the project legend sheet.
German (DIN): Armatur, normal geschlossen. See DIN P&ID symbols.
Where you see it on a P&ID
On bypasses, drains, vents, cross-connections and spare connections.
Tag codes
The normally closed valve is commonly tagged:
- NC
- LC
- CSC
Tag formats follow the project numbering procedure. For instruments, the letters follow ISA 5.1, explained on the instrument symbols page.
Related symbols
Frequently asked questions
What does the normally closed valve symbol look like on a P&ID?
A valve body drawn filled solid black, usually with NC beside it. Locked closed valves are marked LC, and car-sealed closed valves CSC.
What is a normally closed valve used for?
A normally closed valve is shut during normal operation and only opened for start-up, maintenance or emergencies. Showing it closed matters for every isolation and line-up. You will find it on bypasses, drains, vents, cross-connections and spare connections.
What tag does a normally closed valve have?
It is commonly tagged NC, LC, CSC. The exact tag format comes from the project numbering procedure and the legend sheets.
Is the normally closed valve symbol the same in ISA and ISO?
ISO 10628-2 has no separate symbol for this. Check the project legend sheet. Companies vary the details, so always check the legend sheets at the front of the P&ID set.
What is the normally closed valve called in German?
Armatur, normal geschlossen. On a German R&I-Fließschema it is drawn to DIN EN ISO 10628-2.
- In production since 2014
- Thousands of daily users
- On MODEC FPSO projects since 2016