Pressure gauge symbol

A circle on a stem with a pointer or letters, marking a pressure indicator.

Also known as: Instrument bubble, PI instrument code, Circle with letters on a pipe

Engineering & technicalQuiet profile

Meanings

A circle on a short stem marks an instrument. The letters inside say what it measures and what it does — PI for pressure indication, PT for a transmitter — so the circle is a container for a code rather than a picture.

Common modern usageVerified fact
Marks an instrument measuring pressure at that point in the system, drawn as a circle joined to the pipe by a short stem.
Contexts: Technical drawing
Common modern usageVerified fact
Carries a letter code stating what is measured and what the instrument does, so PI is a pressure indicator and PT a pressure transmitter.
Contexts: Technical drawing
Common modern usageVerified fact
Uses the line style of its stem to say where the instrument is mounted and how its signal travels — a solid line for a local gauge, a dashed one for an electrical signal.
Contexts: Technical drawing

Visual description

A circle joined by a short straight stem to a pipeline, with one or two capital letters written inside it and sometimes a horizontal line across its middle.

A fuller structured visual breakdown is not yet documented for this symbol.

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references.

Sources

Piping and instrumentation diagram
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol instructs and which standard governs it. Where a standard is named it is reported by this source rather than read, so no meaning is typed `official` on that basis.
Pressure measurement
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol instructs and which standard governs it. Where a standard is named it is reported by this source rather than read, so no meaning is typed `official` on that basis.

Last reviewed 2026-07-31

Part of

Process and instrumentation diagram (P&ID) and circuit symbols

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Meanings

Common modern usageVerified fact

Marks an instrument measuring pressure at that point in the system, drawn as a circle joined to the pipe by a short stem.

Contexts: Technical drawing

Common modern usageVerified fact

Carries a letter code stating what is measured and what the instrument does, so PI is a pressure indicator and PT a pressure transmitter.

Contexts: Technical drawing

Common modern usageVerified fact

Uses the line style of its stem to say where the instrument is mounted and how its signal travels — a solid line for a local gauge, a dashed one for an electrical signal.

Contexts: Technical drawing

Confidence

IdentityHigh confidence: High confidence because the identity is documented in encyclopedic references.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is documented in encyclopedic references.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references.

Sources

Piping and instrumentation diagram
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol instructs and which standard governs it. Where a standard is named it is reported by this source rather than read, so no meaning is typed `official` on that basis.
Pressure measurement
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol instructs and which standard governs it. Where a standard is named it is reported by this source rather than read, so no meaning is typed `official` on that basis.

Last reviewed 2026-07-31