Pneumatic cylinder selection reference against ISO 15552 (successor to ISO 6431 / VDMA 24562). Covers bore sizing from theoretical force (F = P × A × η), stroke-to-bore ratio guidance to avoid piston-rod buckling, standard bore range 32-320 mm, mounting styles (foot, flange, clevis, trunnion), cushioning options (fixed, adjustable pneumatic, hydraulic shock), and cross-reference between SMC (CDA2, C96), Festo (DSBC, DSBG) and Parker (P1D, P1E) product families.
ISO 15552 (2018) is the current international standard for tie-rod pneumatic cylinders, superseding ISO 6431 (1992) and the earlier VDMA 24562. All three standards specify the same mounting envelope for a given bore, which means a cylinder from any ISO-15552-compliant OEM drops into an existing ISO 6431 / VDMA 24562 machine without modification of the mounting bracket. This is deliberate — the standards evolution has consistently preserved mechanical interchangeability so end-users are not locked to a single supplier.
Theoretical force at the piston rod, F = P × A × η, where P is the pilot pressure in Pa, A is the piston effective area in m², and η is the cylinder mechanical efficiency (typically 0.85-0.95 for a well-lubricated fresh cylinder; 0.75-0.85 for a field-worn one after 500,000 cycles). For retraction stroke on a double-acting cylinder, subtract the piston rod area from A. Design practice is to add a load factor of 1.3-1.5 above the required load to account for pressure drop across supply valves and wear-induced efficiency loss.
| Bore Ø (mm) | Piston area (mm²) | Force at 6 bar extension (N) | Force at 6 bar retraction (with 20 mm rod) |
|---|---|---|---|
| 32 | 804 | 482 | 294 (12 mm rod) |
| 40 | 1257 | 754 | 566 (16 mm rod) |
| 50 | 1963 | 1178 | 962 (20 mm rod) |
| 63 | 3117 | 1870 | 1550 (20 mm rod) |
| 80 | 5027 | 3016 | 2565 (25 mm rod) |
| 100 | 7854 | 4712 | 4098 (25 mm rod) |
| 125 | 12272 | 7363 | 6558 (32 mm rod) |
| 160 | 20106 | 12064 | 11056 (40 mm rod) |
| 200 | 31416 | 18850 | 17275 (40 mm rod) |
| 250 | 49087 | 29452 | 27100 (50 mm rod) |
A pneumatic piston rod acts as a slender column under compression on the extension stroke. Long strokes at small bore make the rod susceptible to Euler buckling. Cylinder manufacturers publish a buckling diagram (force vs stroke) for each bore-and-rod combination; the design point must sit below the curve after applying a safety factor of 3.5 (or higher for mounting styles that permit rod rotation). As a rule of thumb, keep stroke ≤ 15 × bore for foot-mounted cylinders and ≤ 20 × bore for cylinders with rod-end mounting that constrains rotation.
| Code | Style | Best for |
|---|---|---|
| MP1 / MP2 | Foot mount | Rigid frame installation, no misalignment |
| MF1 / MF2 | Front / rear flange | Through-plate mount, tension or compression |
| MS1 / MS2 | Side lug (rectangular) | Machine cabinets, standardised bolt pattern |
| MT4 | Trunnion (rotating pivot mid-body) | Rotating load, swing arm |
| ME1 / ME2 | Male / female clevis at rear | Angular displacement between fixed pivot points |
| MP4 | Male clevis with pin | Simple pin-jointed load |
At end of stroke, unrestrained impact of the piston against the end cap damages the cylinder over time. Cushioning options: fixed cushion (rubber bumper — light-load, low-speed only), pneumatic adjustable cushion (throttling exhaust port, screw-adjustable; standard on ISO 15552 cylinders), external hydraulic shock absorber (heavy loads, high speed, mounted separately). Adjustable pneumatic cushioning is the default choice — set once at commissioning with a stopwatch or accelerometer to a smooth deceleration profile.
| ISO 15552 | SMC | Festo | Parker |
|---|---|---|---|
| Standard tie-rod (Ø 32-320) | CDA2, C96 | DSBC, DNC | P1D-S, P1D-B |
| Standard tie-rod, low-friction | CDA2W | DSBG | P1E |
| Compact (short-stroke) | CDQ2 | ADN | P1P |
| ATEX / IECEx (Zone 1/21) | CD*-XC22 | DSBC/DSBG-EX | P1D-EX |
| Stainless (food / pharma) | C96SC / CDA2S | DSBG-CI | P1D-C |