Pneumatics · beginner
Double-Acting Pneumatic Cylinder
A linear air-powered actuator. Compressed air pushes a piston to extend or retract a rod that moves part of a machine.
Why it exists
Create simple, fast linear motion for clamping, lifting, pushing, sorting, and positioning.
Quick answer
What is a double-acting pneumatic cylinder?
A double-acting pneumatic cylinder turns air pressure into straight-line motion. A directional valve sends pressure to one side of the piston while the opposite chamber exhausts; reversing the valve reverses the force and rod direction. End sensors report retracted and extended positions back to the PLC.
Inside the control system
How the PLC relates to it
The PLC should command the valve and wait for the appropriate end sensor rather than assuming motion completes after a fixed delay. A robust sequence prevents extend and retract commands from conflicting, starts a travel timeout, and stops or recovers deliberately if the expected limit never arrives. Reed switches prove position only where they are mounted; they do not measure force, speed or whether tooling safely completed its work. For vertical loads, loss of air and stored-energy behaviour need explicit engineering controls.
Cause and effect
How it works, step by step
- 01
The valve supplies air to one side of the piston.
- 02
Pressure acting over piston area creates linear force.
- 03
Air on the opposite side exhausts through the valve.
- 04
End switches confirm that the cylinder really reached its commanded position.
01 / Open the case
Watch the mechanism do the work
Follow one highlighted causal link at a time, then operate the component and deliberately create the fault.
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Know the terminals
- Cap-end air port
- Rod-end air port
- Extend reed switch
- Retract reed switch
Recognise the faults
- Air leak or low pressure
- Flow control fitted in wrong direction
- Side load damages seals
- Command changes without end-position proof
Read the field guide
Go deeper on sizing, wiring conventions, test procedure, and the mistakes that damage equipment.
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Selection checks
- Required force from pressure and effective piston area, including losses and safety margin.
- Stroke, mounting style, side-load capacity and available space.
- Speed, cushioning and flow-control arrangement.
- Magnetic piston and sensor type for end-position feedback.
- Behaviour on loss of air, trapped pressure and vertical-load risk.
Commissioning sequence
- 1Confirm cylinder bore, stroke, mounting and load direction before applying air.
- 2Connect cap-end and rod-end ports to the correct valve outlets and set conservative flow control.
- 3Jog extend and retract while observing the mechanical travel and both end sensors.
- 4Adjust sensor positions so each indication changes reliably at the true end of stroke.
- 5Measure travel time under load, set a reasonable PLC timeout and test jam or low-pressure detection.
Troubleshooting answers
Frequently asked questions
Why use two end sensors on a cylinder?
They give independent proof of the retracted and extended states, allowing the PLC to sequence safely and diagnose a command that did not complete.
Should cylinder speed be controlled by restricting supply or exhaust?
Many pneumatic applications use meter-out control, restricting exhaust to improve stability. The correct arrangement depends on the load, valve and cylinder, so follow the pneumatic design guidance.
How should PLC logic handle a cylinder jam?
Start a timeout when motion is commanded, stop dependent actions if the expected limit does not arrive, remove or place outputs in the defined safe state, and require a deliberate recovery after the cause is addressed.
Now use it in a machine
Recognition is not mastery. Build the control logic, operate the process, and prove the fault response.
Free first success
Now control a double-acting pneumatic cylinder in a working machine
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