Pneumatic 3/2 Valve Symbol

The Pneumatic 3/2 Valve schematic symbol. Standard-specific details are listed below where available.

Definition: The Pneumatic 3/2 Valve symbol represents a directional control valve with 3 ports and 2 switching positions used in compressed-air circuits to control the extension and retraction of single-acting pneumatic cylinders, standardised under ISO 1219-1 and represented with terminals P (pressure/supply), A (work/output), and R (exhaust).

Also known as: 3/2 directional control valve, 3-port 2-position valve, 3/2 solenoid valve, pneumatic 3/2 valve, single-acting cylinder control valve, normally-closed 3/2 valve, normally-open 3/2 valve.

What the Pneumatic 3/2 Valve symbol means

The Pneumatic 3/2 Valve symbol represents a directional control valve that has exactly three ports — one pressure supply port (P), one working port (A), and one exhaust port (R) — and two discrete switching positions. In the rest (normal) position, either P is connected to A (normally open) or A is connected to R (normally closed), depending on the valve type. When the valve is actuated (by a solenoid, pilot air, manual lever, or spring), it shifts to the second position and reverses those connections.

In pneumatic circuit diagrams, the 3/2 valve symbol is the standard control element for single-acting cylinders (cylinders with one air port and an internal return spring). Pressing the actuator feeds pressurised air to the cylinder through port A, extending the piston; releasing the actuator shifts the valve so port A is exhausted through port R and the return spring retracts the piston. The 3/2 valve symbol appears on every pneumatic circuit drawing that controls a single-acting actuator.

How to identify the Pneumatic 3/2 Valve symbol

The 3/2 valve symbol is drawn as two side-by-side rectangles (each representing one switching position) with arrows and lines inside showing the port connections in each position. In position 1 (normal), the connection path between P, A, and R is shown by lines and arrows within the left rectangle; in position 2 (actuated), the alternative connections are shown in the right rectangle. The port labels P (pressure supply, enters from below one rectangle), A (work port, exits from the top or side), and R (exhaust, exits downward) are marked outside the rectangle boxes. An actuator symbol (a spring for return, a solenoid coil box, or a pushbutton symbol) is drawn at one or both ends of the two-rectangle valve body.

Function and usage boundary

A 3/2 valve directs compressed air flow between its three ports in two distinct configurations. In normally-closed (NC) configuration: resting state connects A to R (cylinder is vented); actuated state connects P to A (cylinder pressurised and extends). In normally-open (NO) configuration: resting state connects P to A (cylinder pressurised); actuated state connects A to R (cylinder vents and retracts). The valve may be actuated by a solenoid coil energised from a PLC output, a manual push-button, a pneumatic pilot signal, a roller cam, or a combination of these. Flow rates are characterised by the valve's Cv (flow coefficient) and nominal bore size.

Standards: IEC vs ANSI

IEC 60617	ISO 1219-1:2012 (fluid power systems and components — graphical symbols and circuit diagrams) defines the 3/2 valve symbol as two adjacent position rectangles with port labelling P, A, R (or T for tank in hydraulic variants). This is the internationally recognised standard used throughout Europe, Asia, and internationally for pneumatic circuit diagrams.
ANSI/IEEE 315	ANSI/NFPA T3.3.7 R1 (pneumatic fluid power) uses essentially the same graphical conventions as ISO 1219-1 for pneumatic directional control valve symbols. Both use the two-rectangle format with port labels; ANSI practice uses the same P/A/R designations. Valve reference designator: V or SV (solenoid valve).
Key difference	ISO 1219-1 and ANSI/NFPA T3.3.7 use the same graphical convention for directional control valves. The primary difference is in documentation conventions: ISO drawings may label ports P/A/R or 1/2/3 (port numbers per ISO 5599-3); ANSI drawings typically use P/A/R or inlet/outlet/exhaust text labels. Functionally and graphically the symbols are identical.

The displayed SVG is the live editor implementation, not a licensed reproduction or certification of an IEC or IEEE database glyph. Verify the exact official entry and project edition before issuing work.

Logical terminals

Logical ID	Editor terminal name
p	P (Supply)
a	A (Work)
r	R (Exhaust)

Where the Pneumatic 3/2 Valve symbol is used

Control of single-acting pneumatic cylinders (spring-return) in pick-and-place automation
Pneumatic clamping and unclamping fixtures on CNC machining centres
Blow-off and air-jet nozzle control in parts cleaning and conveyor systems
Pneumatic pilot signal supply and exhaust in vacuum generator circuits
Emergency stop and safety dump circuits that vent actuators when de-energised (NC configuration)
Simple push-button controlled pneumatic press or stamping machine actuation

Key facts

The Pneumatic 3/2 Valve symbol has two adjacent position rectangles showing port connections in each state, with three ports: P (pressure supply), A (work/output to actuator), and R (exhaust).
3/2 means: 3 ports, 2 positions — the valve shifts between exactly two discrete connection configurations.
Standardised in ISO 1219-1:2012 and ANSI/NFPA T3.3.7; valve reference designator V or SV on pneumatic circuit diagrams.
Normally-closed (NC) 3/2: rest position connects A to R (actuator vented); actuated position connects P to A (actuator pressurised).
Normally-open (NO) 3/2: rest position connects P to A (actuator pressurised); actuated position connects A to R (actuator vented).
The return mechanism (spring, pilot, manual) is shown as a symbol at one end of the two-rectangle valve body; solenoid actuation is shown at the other end.
3/2 valves are specifically suited to single-acting cylinders that have one air port and rely on an internal spring for return stroke.
Typical solenoid coil voltages: 12 V DC, 24 V DC (most common in industrial PLC systems), 110 V AC, or 230 V AC.

Frequently asked questions

What does the pneumatic 3/2 valve symbol look like?

The 3/2 valve symbol shows two side-by-side rectangles (each representing one valve position), with lines and arrows inside each rectangle indicating the port connection paths for that position. Three port labels — P (supply), A (work), and R (exhaust) — are written outside the rectangles. An actuator symbol (solenoid box, spring, push-button, or pilot) is drawn at one or both ends of the two-rectangle body.

What does 3/2 mean in a pneumatic valve?

In pneumatic valve nomenclature, '3/2' means the valve has 3 ports and 2 switching positions. The first number always indicates the number of ports (P, A, R); the second number indicates the number of discrete positions the valve spool can occupy. A 3/2 valve is the simplest directional control valve for single-acting cylinders.

What are the three ports of a 3/2 valve?

The three ports are: P (pressure — connects to the compressed-air supply), A (work — connects to the actuator or cylinder), and R (exhaust/return — vents to atmosphere). In ISO 1219-1 port numbering, P is port 1, A is port 2, and R is port 3.

What is the difference between a normally-closed and normally-open 3/2 valve?

A normally-closed (NC) 3/2 valve has its A port connected to exhaust (R) in the resting de-energised state — the actuator is vented and retracted. When actuated, P connects to A and the actuator extends. A normally-open (NO) 3/2 valve has P connected to A in rest (actuator is pressurised and extended); actuation vents A to R. NC valves are preferred for safety-critical applications where power loss should retract the actuator.

What is the difference between a 3/2 and a 5/2 valve?

A 3/2 valve has 3 ports and 2 positions — suitable for single-acting cylinders with one air port. A 5/2 valve has 5 ports (P, A, B, R, S) and 2 positions — suitable for double-acting cylinders with two air ports (A and B), allowing the cylinder to be pressurised in both extension and retraction directions. The 5/2 valve symbol shows 5 port connections across its two position rectangles.

What standard defines the 3/2 pneumatic valve symbol?

The 3/2 pneumatic directional control valve symbol is defined in ISO 1219-1:2012 (Fluid power systems and components — graphical symbols and circuit diagrams — Part 1: graphical symbols for conventional use and data processing applications). ANSI/NFPA T3.3.7 uses the same conventions for North American pneumatic circuit documentation.

What actuators are used with a 3/2 valve?

3/2 valves are most commonly actuated by a DC solenoid (24 V DC for PLC-controlled automation), a manual push-button (for operator-controlled stations), a pneumatic pilot signal (pilot-operated valve), or a mechanical roller/cam (limit valve). The actuator type is indicated by a specific symbol at the end of the two-rectangle valve body and determines how the valve shifts between its two positions.

Related symbols

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