Spectacle blind symbol
Also called Figure 8 blind, Line blind
A spectacle blind is a plate with a solid disc and an open ring joined together. Turning it isolates the line positively or opens it again.
What the spectacle blind symbol means
A spectacle blind is a plate with a solid disc and an open ring joined together. Turning it isolates the line positively or opens it again.
How it is drawn
A figure 8 between two flanges, with the solid half filled black when the line is closed and the open half shown in the line when open.
The spectacle blind symbol in each standard
Drawn as on most US-style legend sheets.
Interchangeable disc (blind disc). Two discs on a stem across the line. The disc next to the line is the one in use: solid for blind (2044), open for flow (2045).
ISO SVG
German (DIN): Brillensteckscheibe. See DIN P&ID symbols.
Where you see it on a P&ID
At positive isolation points for maintenance, commissioning and tie-ins.
Tag codes
The spectacle blind is commonly tagged:
- NO (normally open)
- NC (normally closed)
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 spectacle blind symbol look like on a P&ID?
A figure 8 between two flanges, with the solid half filled black when the line is closed and the open half shown in the line when open.
What is a spectacle blind used for?
A spectacle blind is a plate with a solid disc and an open ring joined together. Turning it isolates the line positively or opens it again. You will find it at positive isolation points for maintenance, commissioning and tie-ins.
What tag does a spectacle blind have?
It is commonly tagged NO (normally open), NC (normally closed). The exact tag format comes from the project numbering procedure and the legend sheets.
Is the spectacle blind symbol the same in ISA and ISO?
No. Two discs on a stem across the line. The disc next to the line is the one in use: solid for blind (2044), open for flow (2045). The ISO 10628-2 registration number is 2044. Always check the legend sheets at the front of the P&ID set.
What is the spectacle blind called in German?
Brillensteckscheibe. 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