Sight glass symbol
Also called Sight flow indicator
A sight glass is a window in the line that lets operators see the flow, its colour or whether liquid is present.
What the sight glass symbol means
A sight glass is a window in the line that lets operators see the flow, its colour or whether liquid is present.
How it is drawn
A circle in the line with two short lines either side, or a circle with a dot.
The sight glass symbol in each standard
Drawn as on most US-style legend sheets.
Viewing glass. A box in the line with a circle inside. With lighting it is X8089.
ISO SVG
German (DIN): Schauglas. See DIN P&ID symbols.
Where you see it on a P&ID
On lube oil returns, condensate lines and chemical injection.
Tag codes
The sight glass is commonly tagged:
- SG
- FG
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 sight glass symbol look like on a P&ID?
A circle in the line with two short lines either side, or a circle with a dot.
What is a sight glass used for?
A sight glass is a window in the line that lets operators see the flow, its colour or whether liquid is present. You will find it on lube oil returns, condensate lines and chemical injection.
What tag does a sight glass have?
It is commonly tagged SG, FG. The exact tag format comes from the project numbering procedure and the legend sheets.
Is the sight glass symbol the same in ISA and ISO?
No. A box in the line with a circle inside. With lighting it is X8089. The ISO 10628-2 registration number is 2034. Always check the legend sheets at the front of the P&ID set.
What is the sight glass called in German?
Schauglas. 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