Cylinders

Cylinders are linear actuators that convert pneumatic or hydraulic pressure into a controlled push/pull force. They are the most common motion element in industrial automation.

Overview

A cylinder consists of a barrel, piston, rod, end caps, and seals. Pressure on one side of the piston creates force; flow into that side creates motion.

Types

Single-acting — pressure extends, spring retracts (or vice-versa).
Double-acting — pressure on both ports; most common.
Rodless — magnetic / band-coupled; long strokes in tight spaces.
Telescoping — long stroke in short retracted length.
Tandem / duplex — multiplied force.
Through-rod — equal area both sides; equal force & speed.
Rotary actuator — limited-angle rotation (rack & pinion, vane).

Sizing & Force Calculation

Extend force: F = P × A_piston
Retract force: F = P × (A_piston − A_rod)
Piston area: A = π·D²/4
Apply a safety / dynamic factor of ~1.25–2 for sizing.
Check rod buckling per Euler at full stroke extension.
Verify air consumption (pneumatic) — scfm at duty cycle.

Mounting Styles

Foot / side — rigid frame mount.
Flange — at front (head) or rear (cap).
Clevis — pivot at rear; rod end is also pivoted.
Trunnion — pivots at midpoint for angular motion.
Tie-rod mounts (NFPA pneumatic standard MR-series).

Cushioning & Speed

End-of-stroke cushions decelerate the load — adjustable needle valves on most cylinders.
External shock absorbers for high-energy loads.
Speed control: meter-out preferred (back-pressure smooths motion).
Typical pneumatic speeds: 0.1–1 m/s; hydraulic: 0.05–0.5 m/s.

Seals & Maintenance

Rod, piston, wiper, and static seals — typically NBR, FKM (Viton), or polyurethane.
Match seal material to fluid & temperature (mineral oil, water-glycol, food-grade air).
Common failure mode: contamination (dirty air/oil) wearing seals.
Replace rod seals if leakage exceeds vendor spec; resize before installing new seals.