Pneumatic Cylinder (Double Acting) Symbol
Definition: The Pneumatic Cylinder (Double Acting) symbol represents a linear actuator driven by compressed air on both the extend and retract strokes, depicted in fluid-power diagrams per ISO 1219-1 as a rectangle (cylinder body) with a rod emerging from one end and two port triangles — Port A (extend) and Port B (retract) — indicating that pressurised air moves the piston in both directions under active control.
Also known as: double-acting air cylinder, DA pneumatic actuator, two-port air cylinder, double-acting linear actuator.
What the Pneumatic Cylinder (Double Acting) symbol means
The Pneumatic Cylinder (Double Acting) symbol represents an air-powered linear actuator in which compressed air is applied alternately to both sides of the piston to drive extension and retraction under positive control. Unlike a single-acting cylinder that relies on a spring or gravity to return, the double-acting type uses air pressure for both strokes, giving the engineer full control over speed and force in both directions.
In pneumatic circuit diagrams the double-acting cylinder symbol marks the load or end-effector stage of the circuit. It connects to a directional-control valve (typically a 5/2 or 4/2 valve) that switches air between Port A and Port B. The symbol communicates that both stroke directions are powered, which is important for sizing the compressor, valve, and tubing.
How to identify the Pneumatic Cylinder (Double Acting) symbol
The double-acting pneumatic cylinder is drawn as a horizontal rectangle representing the cylinder barrel, with a thin line (piston rod) extending from the right-hand end beyond the barrel wall. Two small triangular port indicators or labelled connection points appear on the barrel: Port A near the cap end (left, rod-retracted side) for the extend stroke, and Port B near the rod end (right) for the retract stroke. A vertical dashed line inside the rectangle represents the piston face. The ISO 1219-1 symbol shows both ports explicitly, distinguishing it from the single-acting variant which shows only one port and a spring symbol.
Function in a circuit
A double-acting pneumatic cylinder converts compressed-air energy into bidirectional linear mechanical force and displacement. When a directional-control valve connects the supply to Port A and vents Port B, the piston extends; reversing the valve pressurises Port B and vents Port A, retracting the piston. Stroke length is fixed by the cylinder bore, and force equals air pressure multiplied by piston area (extend stroke uses full bore area; retract stroke uses bore area minus rod area). Operating pressures typically range from 4 to 10 bar (58 to 145 psi).
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 does not cover pneumatic actuator symbols; fluid-power symbols are standardised under ISO 1219-1:2012 (Fluid power systems — Graphical symbols), which defines the double-acting cylinder as a rectangle with a piston line, rod, and two port connections. |
|---|---|
| ANSI/IEEE 315 | ANSI/NFPA T3.25.3 (based on ISO 1219-1) defines the same rectangular body with two ports for the double-acting cylinder; the symbol is functionally identical to the ISO drawing in both appearance and convention. |
| Key difference | ISO 1219-1 and ANSI/NFPA T3.25.3 use the same glyph for the double-acting cylinder; there is no visual difference between the two standard representations. |
Terminals / pins
| Pin | Name |
|---|---|
| port_a | Port A |
| port_b | Port B |
| rod | Rod |
Typical values
Typical operating pressure: 4–10 bar (58–145 psi); bore diameters: 6 mm to 320 mm (ISO 6432 mini-cylinders to large ISO 15552); stroke lengths: 10 mm to several metres; extend force = pressure × bore area; retract force = pressure × (bore area − rod area); speed: 50–1500 mm/s with flow control.
Where the Pneumatic Cylinder (Double Acting) symbol is used
- Robotic arm joints and pick-and-place machines requiring controlled extension and retraction
- Stamping and pressing machines where both extend force and retract force must be specified
- Conveyor stop-gates and diverters in automated material handling
- Clamping fixtures on CNC machining centres that must grip and release positively
- Automotive assembly-line welding guns needing repeatable stroke force in both directions
- Packaging machine flap-folding and sealing mechanisms
Example
In a parts-assembly cell, the pneumatic circuit diagram shows a 5/2 solenoid directional valve connected to a double-acting cylinder symbol: when solenoid A energises, air flows from the valve to Port A of the cylinder and the piston extends to press a rivet; when solenoid A de-energises and solenoid B energises, air switches to Port B and the piston retracts to the home position, ready for the next cycle.
Key facts
- The double-acting pneumatic cylinder symbol per ISO 1219-1:2012 shows a rectangle with a piston line, a projecting rod, and two labelled air ports (Port A for extend, Port B for retract).
- Both the extend and retract strokes are powered by compressed air, giving full bidirectional force control — the key distinction from a single-acting (spring-return) cylinder.
- Extend force equals supply pressure multiplied by full piston bore area; retract force is slightly lower because the rod occupies part of the piston face area.
- Typical operating pressure range is 4–10 bar (58–145 psi) with bore diameters from 6 mm (ISO 6432 mini) to 320 mm (ISO 15552 tie-rod).
- The double-acting cylinder is governed by ISO 1219-1:2012 and ANSI/NFPA T3.25.3; IEC 60617 does not define pneumatic actuator symbols.
- A double-acting cylinder requires a 4/2 or 5/2 directional-control valve to switch air between Port A and Port B; two flow-control valves (one per port) are used to independently regulate extend and retract speed.
- Common variants include double-acting cylinders with magnetic piston (for reed-switch position sensing), cushioned ends (to decelerate the piston near end of stroke), and through-rod designs (equal force in both directions).
Frequently asked questions
What does the double-acting pneumatic cylinder symbol look like?
The double-acting pneumatic cylinder symbol is a rectangle (the barrel) with a vertical dashed line inside (the piston), a thin line extending from the right end (the rod), and two port connections on the barrel body — Port A at the cap end and Port B at the rod end. Both ports are shown, which is the visual distinction from the single-acting symbol that shows only one port and a spring.
What does the double-acting pneumatic cylinder symbol mean?
The symbol means that compressed air actively drives the piston in both directions: Port A pressurised extends the rod, Port B pressurised retracts it. Both strokes develop positive force from the air supply, and there is no spring for return.
What is the difference between a single-acting and double-acting cylinder symbol?
The single-acting cylinder symbol (ISO 1219-1) shows one air port and a spring symbol inside the barrel indicating spring return. The double-acting symbol shows two air ports and no spring, indicating that both strokes are powered by compressed air.
Which standard defines the double-acting pneumatic cylinder symbol?
The double-acting pneumatic cylinder symbol is defined by ISO 1219-1:2012 (Fluid power systems — Graphical symbols and circuit diagrams). ANSI/NFPA T3.25.3 uses an identical symbol. IEC 60617 covers electrical, not fluid-power, symbols.
What valve is typically paired with a double-acting cylinder?
A 5/2 directional-control valve (5 ports, 2 positions) is the most common choice for a double-acting cylinder. It connects the air supply to Port A while venting Port B in one position, then switches to pressurise Port B and vent Port A in the other position.
Why is the retract force less than the extend force in a double-acting cylinder?
During retraction, air acts on the annular area of the piston face (bore area minus rod cross-section area) because the rod physically occupies part of the face. Extend force uses the full bore area. For equal bidirectional force, a through-rod cylinder (equal rod diameters on both sides) is used.
What pins does the double-acting cylinder symbol have?
The double-acting pneumatic cylinder symbol has two pneumatic ports — Port A (cap-end inlet, drives extension) and Port B (rod-end inlet, drives retraction) — plus the mechanical rod connection point indicating the output shaft. These correspond to the Port A, Port B, and Rod connections shown in the symbol.
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