Pneumatic Cylinder Selection Guide: Bore, Stroke, Mounting & ISO Standards

Choosing the right pneumatic cylinder is the difference between a production line that runs for millions of cycles and one that fails inside a shift. This guide walks engineers through the full selection workflow—force calculation, ISO standard mapping, mounting geometry, cushioning, and seal life—so you can specify with confidence instead of guessing from a catalogue number.

What Is a Pneumatic Cylinder?

A pneumatic cylinder converts compressed-air energy into linear motion. Compressed air enters a chamber, pushes a piston and rod, and produces thrust. The three families you will meet most often:

• Single-acting (SA): air drives the piston in one direction; a spring or external load returns it. Simple, low-cost, ideal for clamping and ejection.
• Double-acting (DA): air drives the piston in both directions. Higher force density and precise two-way control—the default for automation.
• Rodless (magnetic or cable): the load moves with the piston externally, giving full stroke in roughly half the installed length. Used where space is tight.

ISO Standards You Must Know

Matching the ISO profile protects you from vendor lock-in and guarantees interchangeability. The three profiles below cover 95% of industrial needs:

For 3C electronics and injection-molding tooling, ISO 6432 and ISO 21287 compact profiles dominate because they fit where space is at a premium. See our pneumatic cylinder guide for plastic injection molding for a worked example.

How to Size a Pneumatic Cylinder (Force Calculation)

The core equation is brutal in its simplicity:

F = P × A — where F is available thrust (N), P is effective air pressure (Pa), and A is piston area (m²).

Always derate for friction (≈10–15%) and use the minimum line pressure, not the compressor nameplate. A practical bore-vs-force table at 6 bar:

Size for the worst-case dynamic load plus a 1.5–2× safety factor. Undersizing is the #1 cause of premature seal failure.

Mounting Styles & When to Use Them

Speed, Cushioning & Stroke Length

Standard cylinders run 0.1–1.0 m/s. Above 0.5 m/s, specify end-of-stroke cushioning (pneumatic or adjustable) to kill impact energy and protect tooling. Stroke should be the mechanical travel plus a 5–10 mm safety margin—never “round up to the next catalogue size” without checking cycle life.

Seal Materials & Service Life

Seal choice sets your maintenance interval. NBR handles −20°C to +80°C and most workshops. PU gives lower friction and longer life on high-cycle lines. FKM resists heat and oils but costs more. Our cylinder maintenance guide on seal materials and service life breaks down the trade-offs with a replacement schedule.

Common Selection Mistakes

• Sizing on nameplate pressure instead of minimum line pressure.
• Ignoring side loads—use a guide or external rail.
• Skipping cushioning on fast strokes.
• Mixing ISO profiles across a line, breaking spare-part commonality.

Applications in 3C & Injection Molding

In electronics and plastic injection molding, cylinders drive ejectors, core pulls, and fixture clamps where repeatability beats raw force. Compact ISO 6432 bodies and non-lubricated seals keep cleanrooms viable. Carroland has supplied Foxconn-certified pneumatic fixtures for iPhone production lines since 1992, pairing European cylinder technology with China manufacturing for cost-sensitive, high-volume lines.

Related Guides

• Pneumatic Cylinder for Plastic Injection Molding
• Cylinder Maintenance: Seal Materials & Service Life
• Pneumatic Valve & Solenoid Guide
• Pneumatic Actuator Selection Guide
• Pneumatic Cylinders for Electronics Manufacturing
• Parts of a Pneumatic System Explained

Frequently Asked Questions

What ISO standard applies to most pneumatic cylinders?

ISO 15552 covers the majority of standard tie-rod cylinders (32–320 mm bore) and is interchangeable with the older ISO 6431 and VDMA 24562. Compact lines use ISO 6432 (8–25 mm) or ISO 21287.

How do I calculate pneumatic cylinder force?

Use F = P × A, where P is effective pressure in pascals and A is the piston area. Always apply a 10–15% friction derate and size against the minimum line pressure, not the compressor maximum.

When do I need cushioning on a cylinder?

Specify end-of-stroke cushioning whenever piston speed exceeds roughly 0.5 m/s, or whenever the load is delicate tooling. Cushioning absorbs impact energy and extends both seal and component life.

Single-acting or double-acting cylinder?

Use single-acting for simple clamp/eject where a spring return is acceptable. Use double-acting whenever you need controlled force in both directions or precise positioning.

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