Pneumatic Actuators

Actuators convert compressed air energy into mechanical motion. They are the "muscles" of any pneumatic system.

Actuator Types

1. Linear Actuators (Cylinders)

Cylinders produce straight-line motion and are the most common pneumatic actuators.

Single-Acting Cylinder:
┌─────────────────────────┐
│ ←─────── Stroke ──────→ │
│  ┌───┐              ┌─┐ │
│  │   │══════════════│●│→│ Extend (air pressure)
│  │   │              └─┘ │
│  └───┘   Spring ────→   │ Retract (spring return)
└─────────────────────────┘

Double-Acting Cylinder:
┌─────────────────────────┐
│  Port A           Port B│
│    ↓                 ↓  │
│  ┌───┐              ┌─┐ │
│ →│   │══════════════│●│→│ Extend (pressure on A)
│ ←│   │══════════════│●│←│ Retract (pressure on B)
│  └───┘              └─┘ │
└─────────────────────────┘

Cylinder Types

Type	Description	Application
Single-acting	Air extends, spring returns	Light duty, clamping
Double-acting	Air extends and retracts	Most industrial applications
Rodless	Piston travels inside sealed tube	Long strokes, space constraints
Tandem	Two pistons in series	Double force in same diameter
Impact	Designed for high-speed striking	Riveting, stamping
Guided	Built-in linear guides	High side-load applications

Force Calculation

$$F = P \times A$$

Where:

• $F$ = Force (lbs or N)
• $P$ = Pressure (PSI or bar)
• $A$ = Piston area (in² or cm²)

Example: 4" bore cylinder @ 80 PSI

$$A = \pi \times r^2 = \pi \times 2^2 = 12.57 \text{ in}^2$$ $$F_{extend} = 80 \times 12.57 = 1{,}006 \text{ lbs}$$

Retract Force

Retract force is less due to rod area:

$$F_{retract} = P \times (A_{piston} - A_{rod})$$

Air Consumption

$$Q = \frac{A \times S \times n \times (P + 14.7)}{14.7}$$

Where:

• $Q$ = Air consumption (CFM)
• $A$ = Piston area (in²)
• $S$ = Stroke (inches)
• $n$ = Cycles per minute
• $P$ = Operating pressure (PSIG)

2. Rotary Actuators

Convert compressed air to rotational motion.

Vane Type

        ┌───────────┐
       ╱     ═══    ╲
      │    ╱───╲     │
      │   │  ●  │←───│── Vane
      │    ╲───╱     │
       ╲     ═══    ╱
        └───────────┘

• Rotation: 90° to 360°
• Torque: Low to medium
• Simple construction

Rack and Pinion

     Pinion
       ●
      ╱│╲
─────═══════───── Rack (linear motion)
      ↓
  Rotary output

• Rotation: 90° to 720°+
• Torque: Medium to high
• Precise positioning

Type	Rotation Range	Torque	Best For
Vane	90-360°	Low-Med	Valve actuation
Rack & Pinion	90-720°	Med-High	Indexing, positioning
Scotch Yoke	90°	Very High	Large valves, dampers

3. Grippers

Specialized actuators for holding and manipulating objects.

Parallel Gripper:        Angular Gripper:
    ┌─┐    ┌─┐              ╲    ╱
    │ │←──→│ │               ╲  ╱
    │ │    │ │                ╲╱
    └─┘    └─┘                ╱╲
   Open   Close             Open

Type	Motion	Application
Parallel	Jaws move parallel	Precise positioning
Angular	Jaws pivot	General handling
Three-jaw	Self-centering	Round objects
Vacuum	Suction cups	Flat, smooth surfaces

Actuator Selection Criteria

1. Load Requirements

Factor	Consideration
Force needed	Size cylinder accordingly
Speed requirements	Affects flow control needs
Duty cycle	Continuous vs. intermittent
Stroke length	Determines cylinder size

2. Environmental Factors

Condition	Solution
Corrosive	Stainless steel, special seals
High temperature	High-temp seals (Viton, PTFE)
Cleanroom	Low-particle designs
Washdown	IP69K rated

3. Mounting Options

Foot mount:    Flange mount:   Clevis mount:   Trunnion:
  ┌───┐          ╭───╮            ◇              ○──┐
  │   │          │   │           ╱│╲            ════│
══╧═══╧══        ╰═══╯          ╱ │ ╲           ○──┘

Cushioning

Cylinders moving at high speed need deceleration to prevent impact damage.

Cushion Types

1. Fixed cushion - Built-in, non-adjustable
2. Adjustable cushion - Needle valve controls deceleration rate
3. External shock absorbers - For heavy loads or high speeds

Adjustable Cushion Detail:
        ← Plunger enters cushion chamber
┌───────┬─────────────────┐
│░░░░░░░│                 │
│░░░░░░░│     Piston      │→
│░░░░░░░│                 │
└───────┴─────────────────┘
   ↑
Cushion chamber - air must exhaust through
needle valve, slowing piston

Best Practice

Use cushions when piston speed exceeds 1-2 ft/sec or when stopping heavy loads.

Common Cylinder Bore Sizes

Bore (inches)	Bore (mm)	Typical Force @ 80 PSI
3/4"	20	35 lbs
1"	25	63 lbs
1-1/2"	40	141 lbs
2"	50	251 lbs
3"	80	565 lbs
4"	100	1,006 lbs
6"	160	2,262 lbs

Actuator Maintenance

Issue	Cause	Solution
Slow operation	Worn seals, low pressure	Check pressure, replace seals
Erratic motion	Air in system, sticky valve	Bleed air, check valve
Leaking	Worn seals	Replace seal kit
Won't move	No air, stuck valve, seized	Systematic troubleshooting

Seal Life

Cylinder seals have finite life. Plan for replacement every 1-5 million cycles depending on conditions.