Check valve symbol

A ball or flap against a seat, permitting flow one way only.

Also known as: Non-return valve, One-way valve, Ball against a seat

Engineering & technicalStandard profile

Meanings

A check valve permits flow in one direction and blocks the reverse. Its symbol shows the mechanism rather than an arrow, so a reader can see *why* it is one-way rather than merely being told.

Common modern usageVerified fact
Marks a valve permitting flow in one direction only and closing against reverse flow.
Contexts: Technical drawing
Common modern usageVerified fact
Draws the mechanism — a ball or flap seated against a stop — rather than an arrow, so the direction is visible from the geometry.
Contexts: Technical drawing

Visual description

A valve body with a small circle or flap drawn against an angled seat on one side, so the closing direction is evident from the drawing.

Symmetry: none
Orientation: orientation independent

Part of the same system as: Gate valve symbol
Valve symbols on a process diagram.

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

Check valve
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.
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.

Last reviewed 2026-07-31

Part of

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

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Meanings

A check valve permits flow in one direction and blocks the reverse. Its symbol shows the mechanism rather than an arrow, so a reader can see *why* it is one-way rather than merely being told.

Common modern usageVerified fact

Marks a valve permitting flow in one direction only and closing against reverse flow.

Contexts: Technical drawing

Common modern usageVerified fact

Draws the mechanism — a ball or flap seated against a stop — rather than an arrow, so the direction is visible from the geometry.

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

Check valve
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.
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.

Last reviewed 2026-07-31

Meanings

Visual description

Related & commonly confused symbols

Meanings

Visual description

Related & commonly confused symbols