| name | pneumatic-cylinder |
| description | Pneumatic cylinder — force/speed, cushioning, air consumption, ISO 15552/6432, cylinder selection, piston rod buckling, seals, FRL sizing, actuator types. |
| metadata | {"priority":7,"promptSignals":{"phrases":["pneumatic cylinder","air cylinder","pneumatic actuator","cylinder force","air consumption cylinder","ISO 15552","pneumatic cushion"],"minScore":3}} |
Pneumatic Cylinder — Complete Skill
Force Output
Extend force (cap end):
F_extend = P_supply × A_piston - P_back × A_rod_side - F_friction
A_piston = π D²/4
Retract force (rod end):
F_retract = P_supply × (A_piston - A_rod) - P_back × A_piston - F_friction
A_rod = π d_rod²/4
Net (annular) area:
A_net = π/4 × (D² - d_rod²)
Friction:
F_friction ≈ 5–12% of theoretical force (standard seals, good condition)
For high side loads: F_friction increases dramatically (contact force × μ_seal)
Practical rule — usable force:
F_usable = 0.80 × P_supply × A_piston (accounts for friction + back-pressure)
Typical Operating Pressures
Standard plant air: 0.6–0.8 MPa (6–8 bar)
ISO 15552 bore range: 32 to 320 mm diameter
ISO 6432 (mini cylinder): 8 to 25 mm diameter
Velocity and Cylinder Speed
Free-running velocity:
v = Q_in / A_piston [m/s]
Flow required:
Q = v × A × (P_abs / P_atm) × 60,000 [L/min, P in bar-g]
Flow through standard valve (Cv):
v_cylinder = Cv × 12.5 × √(ΔP_valve / P_in) / A_piston [m/s; Cv in SCFM/psi^0.5 units]
Typical velocities (unloaded):
Low speed: 50–150 mm/s (using flow control valves)
Standard: 100–500 mm/s
High speed: 0.5–3 m/s
Speed control: meter-out preferred (downstream throttle → better damping, less chance of jerk)
Air Consumption
Per cycle (double-acting, full stroke S):
V_cycle = S × (A_piston + A_net) × (P_abs / P_atm) × 1000 [L/cycle, P in bar-abs]
Or:
V_extend = (A_piston × S / 1000) × (P + 1.013)/1.013 [liters, P in bar-g, S in mm]
V_retract = (A_net × S / 1000) × (P + 1.013)/1.013
Compressor demand:
Q_compressor = V_cycle × n_cycles/min [L/min at standard conditions]
Cushioning
Built-in adjustable cushions absorb kinetic energy at end of stroke
Cushion onset: typically 20–30 mm from end of travel
Kinetic energy to absorb:
KE = ½ m v² [J]
Self-adjusting cushions: non-adjustable; needle valve with check valve; suitable for variable loads
Fixed cushions: set before operation; precision applications
External shock absorber:
KE_max = ½ m v² + F_push × stroke_absorber
Size absorber: rated energy capacity > 1.5 × KE_max (safety factor)
Piston Rod Buckling
Euler column (fixed-free = worst case, flag ℓ for pneumatic mounting):
F_cr = π² E I / (2L)² [N]
I = π d_rod⁴/64
Mounting factor (Le = effective length):
- FF (pin-pin): L_e = L
- FP (fixed-pin): L_e = 0.7L
- FF (fixed-free, cantilevered): L_e = 2L
- PP (fixed-fixed): L_e = 0.5L
Design requirement:
F_applied < F_cr / SF (SF = 3–4 for pneumatic)
Rod diameter selection (per ISO 15552):
| Bore [mm] | Rod diam [mm] |
|---|
| 32 | 12 |
| 50 | 16 |
| 80 | 22 |
| 125 | 32 |
| 200 | 50 |
FRL Unit Sizing (Filter-Regulator-Lubricator)
Port size from flow requirement:
Q_FRL = sum of all cylinder demands × 1.5 service factor
Pressure drop through FRL:
ΔP ≤ 0.05 MPa (0.5 bar) at maximum flow (maintain 90% pressure at cylinder)
Filter rating:
Standard cylinders: 40 μm; servo/proportional: 5 μm; valves: 25 μm
Regulator:
Accuracy: ±0.02 MPa; set 10–15% above required cylinder pressure
Cylinder Types
Double-Acting (most common)
Both extend and retract are powered; cushions in both directions available
Single-Acting / Spring Return
One end pressurized; spring returns; spring force reduces net extend force:
F_net = P × A - F_spring
Rodless Cylinder
No external rod; piston connected magnetically or via slot-seal to external carriage
Long strokes (up to 10 m); no rod buckling concern; payload on carriage
Linear guides required
Rotary Actuator (pneumatic)
Vane type: 90°/180°/270° rotation; torque = P × V_displacement / (2π × rev)
Rack-and-pinion type: more accurate; better for high torque
Seals and Life
Standard seals: NBR (nitrile) — good for mineral oil, standard temps (-20 to +80°C)
High-temp: PTFE, FKM (to +150°C)
Low-temp: silicone (-60 to +150°C)
Food grade: FDA-approved NBR or EPDM; use food-grade grease
Expected life:
Standard service: 1,000–5,000 km piston travel or 10–50 million cycles
Contaminated: significantly shorter; use appropriate filtration
Output
Provide: F_extend [N], F_retract [N], v_cylinder [m/s] at given flow, Q_air_consumption [L/cycle and L/min], cushion KE to absorb [J], piston rod buckling load limit [N], FRL port size, seal material recommendation, bore × stroke [mm × mm] per ISO 15552.
