Choosing Pneumatic Cylinder Bore & Stroke

Force output calculation

The force produced by a pneumatic cylinder depends on bore diameter, air pressure, and whether you are calculating push (cap end / full bore) or pull (rod end / annular area). For a double-acting cylinder, push force is always greater than pull force because the rod reduces the effective area on the return stroke.

Use the formula: Force (N) = Pressure (bar) × Area (cm²) × 10. For push force, area = π/4 × bore². For pull force, subtract the rod cross-sectional area from the bore area. At 6 bar on a 63 mm bore cylinder, push force ≈ 6 × 31.2 × 10 ≈ 1870 N.

Applying a safety factor

Never size a cylinder for exactly the calculated force. Apply a safety factor of 1.25–1.5 for static loads and 1.5–2.0 for dynamic or vertical loads where gravity adds to the required force. Friction in guides, seals, and linkages also consumes force — account for 5–15% additional depending on mechanism design.

For vertical lifting applications, the cylinder must hold the load on the rod-end (pull) stroke during retraction. Calculate pull force separately and ensure it exceeds the load weight plus friction.

• Static horizontal load — safety factor 1.25
• Dynamic or cycling load — safety factor 1.5
• Vertical lifting — safety factor 1.5–2.0, calculate pull force
• Add 5–15% for guide and seal friction

Stroke length selection

Stroke is the linear distance the piston travels between fully retracted and fully extended positions. Measure the required movement in the application and add a small margin (5–10 mm) for adjustment and end-cap clearance.

Standard strokes follow ISO preferred lengths: 25, 50, 80, 100, 125, 160, 200, 250, 320, 400, 500, 630, 800, 1000 mm and beyond. Non-standard strokes are available but carry longer lead times and premium pricing.

• Measure required travel in the application
• Add 5–10 mm margin for adjustment
• Standard ISO strokes are stocked — non-standard are made to order
• Long strokes (>500 mm) may need external guidance to prevent rod buckling

Standard cylinder profiles

ISO 15552 (formerly ISO 6431) is the most common profile for general industrial automation — tie-rod construction, standard mounting interfaces, and bores from 32 to 320 mm. ISO 6432 covers compact round-body cylinders for space-constrained applications. ISO 21287 covers compact cylinders with integrated mounting.

Confirm the profile matches existing equipment when replacing cylinders on automated lines — mounting dimensions, port positions, and cushion options vary between profiles and manufacturers.

Mounting and load guidance

Cylinder mounting style affects load capacity and side-load tolerance. Basic mountings include foot, flange, trunnion, clevis, and rod-end joint. Side loads on the rod — forces perpendicular to the stroke axis — damage seals and guides rapidly.

If the application applies side load, use external guides (linear bearings, guide rods) or select a cylinder with integrated guide rods (guided cylinder). Never rely on the cylinder rod alone to support lateral forces.

• Foot mount — standard, suitable for straight push/pull
• Flange mount (MF1/MF2) — front or rear, for fixed body applications
• Trunnion mount — pivoting body, for arc motion
• Clevis + rod joint — for pivoting end connections
• Guided cylinder — integrated guide rods for side-load resistance

Port size, cushioning, and speed

Port size affects air flow and therefore cylinder speed. Undersized ports restrict exhaust flow and limit speed. Standard port sizes for ISO 15552 cylinders: G1/8 for bores up to 40 mm, G1/4 for 50–63 mm, G3/8 for 80–100 mm, G1/2 for 125 mm and above.

Adjustable pneumatic cushioning at the end of stroke reduces impact on high-speed applications. Magnetic piston rings enable position sensing with reed switches or Hall sensors — specify if your automation requires position feedback.

• Port size scales with bore — confirm G-thread (BSP) size
• Adjustable cushion — required for speeds above ~0.5 m/s
• Magnetic piston — for reed switch or sensor position feedback
• Speed control — flow regulators on exhaust ports for each direction

What to send for a quote

Complete application data ensures the correct cylinder is quoted first time. If replacing an existing cylinder, provide the manufacturer part number or a photo of the cylinder body marking — bore, stroke, and mounting are often stamped on the barrel.

• Required force or load mass (kg) and orientation (horizontal/vertical)
• Operating pressure (bar) — typically 4–6 bar in UAE plants
• Required stroke (mm)
• Mounting type (foot, flange, clevis, etc.)
• Profile preference (ISO 15552, compact, etc.)
• Cushion and sensor requirements
• Existing part number or photo if replacement

Common mistakes to avoid

• Sizing bore for push force but ignoring reduced pull force on vertical lifts
• Selecting stroke exactly equal to required travel with no adjustment margin
• Applying side loads to the rod without external guidance
• Undersizing ports for high-speed applications — cylinder cannot reach required cycle time
• Mixing ISO profiles on the same machine — mounting dimensions differ
• Ignoring friction in force calculation — especially on guided slides and pivots
• Omitting cushion specification on high-speed or heavy end-of-stroke applications

RFQ checklist

• Load mass (kg) or required force (N)
• Load orientation — horizontal, vertical lift, or angled
• Operating pressure (bar)
• Required stroke (mm)
• Cycle speed or time requirement if critical
• Mounting type and connection style
• ISO profile or existing part number
• Cushion and position sensor requirements