I've been fixing pneumatic cylinders since 2002. Over those years, just about every type you can name has ended up on my bench: single-acting, double-acting, ISO 15552 tie-rods, compact units, rodless ones, and a handful of odd customs where nobody remembers who built them. Customers keep asking the same thing: which cylinder should I actually use? Here's the honest version without the brochure talk.
Single-Acting Cylinders
Simple job, cheap part. Air goes in one side, a spring pushes it back. Use these when you only need force in one direction: clamping a workpiece, ejecting a part, pressing a pin down. Strokes are short (realistically under 80mm) and the return spring is a wearing part, so don't use these in a high-cycle automation line. I see them mostly in stamping units and fixture clamps in Sector 63.
Double-Acting Cylinders
Air both sides. Controlled force going out, controlled force coming back. This is roughly 80% of what we sell. If you're building anything automated (conveyors, pick-and-place, assembly jigs), this is your default. The two shapes you'll see most are ISO 15552 (tie-rod, larger bores) and ISO 21287 (compact). Different beasts.
Compact Cylinders (ISO 21287)
Short body, bolts straight to the machine frame, integrated mounting holes. You use these when the machine designer didn't leave you enough room. Bore 20mm to 100mm. Packaging lines and pick-and-place units in Noida and Greater Noida ask for these constantly. They save 40-50mm of length compared to a tie-rod unit. The trade-off: harder to repair. You can't just unbolt the end caps. When the seals go, it's often cheaper to replace than reseal.
Tie-Rod Cylinders (ISO 15552 / ISO 6432)
If I had to pick one cylinder type for the rest of my career, it'd be these. External tie rods hold the end caps on, which means you can open them up, swap seals, hone the bore, rebuild. ISO 15552 covers the bigger sizes (32-320mm bore); ISO 6432 is the smaller version (8-25mm bore). We repair a lot of these. They were designed to be repairable and it shows.
| Type | Bore range | Best for | Repairable? |
|---|---|---|---|
| Single-acting | 8-80 mm | Clamp, eject, press, one-way force | Sometimes |
| ISO 21287 compact | 20-100 mm | Tight mounting space, packaging lines | Difficult |
| ISO 15552 tie-rod | 32-320 mm | General industrial, conveyors, machine builds | Yes |
| ISO 6432 mini tie-rod | 8-25 mm | Small actuators, lab/assembly rigs | Yes |
| Rodless | 16-80 mm | Long travel without rod projection | Specialist only |
Rodless Cylinders
The piston moves inside the barrel, and the load rides on an external carriage coupled through a slot (mechanical) or magnets. No rod sticks out, so you can get 1.5-3 metre strokes in half the overall length. We sell these occasionally for conveyor stop-and-go mechanisms and transfer systems. Fussier about alignment and not as commonly repaired. Most shops just swap the unit.
How I pick one for a customer
Forget the catalogue for a second. When someone calls me, I ask four questions:
- What's the job? One-direction push or full bi-directional control?
- How much room do you have? Tight mounting → compact. Normal → tie-rod.
- How long a stroke? Over 800mm starts to favour rodless.
- Do you want to repair it later? If yes, tie-rod. Full stop.
That's it. Most of the time a phone call and a photo are enough to decide. If you want a second opinion before you order, WhatsApp +91-9811104037. I'll tell you straight whether the cylinder on the sales quote is the right one.