Pneumatic 3/2 Valve Symbol
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 in a circuit
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. |
Terminals / pins
| Pin | Name |
|---|---|
| p | P (Supply) |
| a | A (Work) |
| r | R (Exhaust) |
Typical values
Typical 3/2 valve specifications: nominal bore 1.5–12 mm; Cv flow coefficient 0.1–2.5; operating pressure 0–10 bar (0–145 psi); solenoid voltage 12 V DC, 24 V DC, or 110/230 V AC; response time 10–50 ms; temperature range -10°C to +60°C; connection G1/8 to G1/2 BSP or 1/8 to 1/2 NPT.
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
Example
In a pneumatic circuit diagram for a parts-clamping station, a 3/2 normally-closed solenoid valve symbol (24 V DC coil) is connected with P from the compressed-air supply manifold and A to the inlet port of a single-acting clamp cylinder. When the PLC output energises the solenoid, the valve shifts from NC position (A exhausted to R) to the second position (P connected to A), extending the clamp. When the PLC de-energises the solenoid, the spring returns the valve to NC and the cylinder spring retracts the clamp.
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.
Place the Pneumatic 3/2 Valve symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.