Safety device symbols
Pressure safety devices protect equipment from overpressure. They are some of the most important symbols to read correctly on a P&ID, because their set pressures and discharge routes are checked in every safety review.
- Pressure safety valveA pressure safety valve opens automatically when pressure rises above its set pressure, releases fluid to a safe place and closes again when pressure falls.
- Rupture discA rupture disc is a thin membrane that bursts at a set pressure to relieve overpressure.
- Flame arrestorA flame arrestor lets gas pass but stops a flame from travelling back through the line, using a fine metal element that cools the flame below ignition.
Safety devices in ISO 10628-2
About ISO 10628-2Relief valves are drawn as angle bodies with a spring, rupture discs as a curved disc between two holders, and flame arrestors as a box with crossed lines.
The cards at the top use the forms of US legend sheets (PIP PIC001 practice). The grids below them show the same symbols as ISO 10628-2 or IEC 62424 draw them. See ISA vs ISO P&ID symbols for the differences.
Frequently asked questions
What are safety device symbols on a P&ID?
Pressure safety devices protect equipment from overpressure. They are some of the most important symbols to read correctly on a P&ID, because their set pressures and discharge routes are checked in every safety review.
How many safety device symbols are there?
This legend covers the 3 most common ones: pressure safety valve, rupture disc, flame arrestor. Project legends may add company-specific variants.
Can I download these symbols?
Yes. Each symbol page has a free SVG and PNG, and the whole legend is available as a printable PDF chart on the P&ID symbols page.