Pneumatic Systems: Components, Operation, and Maintenance

Posted on Nov 28, 2024 in Technology

Item 4: Spare Tire and Circuits

1. Pneumatics and Compressed Air

Pneumatics studies the movement of air under pressure or vacuum. Since 1950, its industrial application began with automation and rationalization. Basic pneumatic circuits consist of: Compressor-Air Tank-Pipes-Maintenance Unit-Quick Connectors-Pressure Hose-Actuator (motor, cylinder, blow gun).

Properties:

  • Inexpensive
  • Air is easily transported and can expel foreign matter
  • Pressure tanks can store energy
  • Less sensitive to temperature variations than oil
  • No fire risk, clean, non-polluting, and causes no vehicle breakdowns
  • Pneumatic components are easier and cheaper to manufacture

Disadvantages:

  • Requires cleaning of abrasive particles, impurities, and moisture
  • Not suitable for high-precision circuits or uniform speed requirements
  • Limited force (6-8 bar)
  • Air exhaust noise (requires silencers)
  • Compressor operation can mix lubricating oil with air
  • Can be more expensive than electricity in some cases

2. Compressors

The first element of pneumatic circuits. They intake and compress atmospheric air to increase its pressure. Main Characteristics:

  • Volume capacity (m³/h)
  • Maximum pressure (bar)

Working Methods:

  • Direct feed to the pneumatic circuit (continuous, low pressure 0.5-2 bar)
  • Storing air in pressure tanks (intermittent, high pressure 6-12 bar)

Drive Types: V-belts, Poly-V belts, Geared, Combustion engine and belt, 12V DC electric motor.

2.1. Piston Compressors

Most common in stationary systems. Similar to a combustion engine, working in 2 strokes (intake/compression and exhaust).

2.2. Membrane Compressors

Reciprocating type, similar to piston compressors but using an elastic membrane for sealing.

2.3. Rotary Compressors

Generate pressure by rotating and compressing air.

  • Rotary Vane: Rotor with vanes sliding in slots, compressing air centrifugally.
  • Lobe (Roots): Two lobes rotate without contact, achieving pressure by resistance. Needs no lubrication, but doesn’t achieve high pressure.
  • Axial: Air is sucked in by turbine blades and compressed by a narrowing outlet.
  • Screw: Two helical screws mesh, compressing air continuously.
  • Rotary Claw: Latest generation, designed for oil-free compressed air, low noise (75dB).

3. Compressed Air Treatment

Air must be cleaned of impurities, abrasive particles, rust, and moisture.

3.1. Abrasive Particle Filtering

Decanters and filters remove particles. Filters have a bleed screw for draining.

3.2. Air Drying

Air contains water vapor, which must be removed to prevent corrosion.

Methods:

  • Cooling: Radiators in the compressor cool the air, condensing water.
  • Absorption: Hygroscopic materials absorb moisture.

3.3. Air Lubrication

Components can run dry or lubricated. Lubrication prevents wear, reduces friction, and protects against corrosion. Uses the Venturi effect (pressure drop in a narrowing passage).

3.4. Pressure Control

Used to provide a lower pressure than the compressor’s output.

3.5. Maintenance Unit

  • Particulate Filter: Removes particles and water droplets.
  • Pressure Regulator: Adjusts output pressure (displayed on a gauge).
  • Lubricator: Sprays oil into the air line.

4. Air Tanks and Accumulators

  • Stabilizes compressed air supply.
  • Allows compressor to stop intermittently.
  • Provides reserve air for safe circuit operation.

Features:

  • Made of steel, spherical or cylindrical for pressure resistance.
  • Have a drain valve at the bottom to remove condensed water. Truck tanks often have automatic drain valves.

5. Pipes

Distribute air from the source to the actuators. Minimize length to avoid pressure drops.

Recommendations:

  • Use elbows instead of straight stretches to minimize pressure drops.
  • Pipe diameter should match flow, pressure, and allowable pressure drop.
  • Closed-circuit systems should have a 2% slope and a drain at the lowest point.
  • Connect air intakes to the main network above water entry points.
  • Include a drain valve in the middle and end of downspouts.

6. Actuators

Convert air pressure into mechanical force. Two types: linear and rotary motion.

6.1. Linear Actuators

Most common type, providing linear movement.

  • Single Effect
  • Double Effect
  • Double Rod
  • Membrane (or Internal Runner)
  • Tandem

6.2. Rotary Actuators (Air Motors)

Convert pressure into rotating motion.

  • Piston Motors: Reciprocating motion, radial or axial pistons.
  • Vane Motors: Most common, simple, lightweight, similar to rotary vane compressors but operating in reverse.

7. Valves

Control the pressure and flow of air in the circuit, enabling automation.

7.1. Command and Control Valves

Channel airflow, opening and closing internal ducts to control pressure and allow air passage. Closing Mechanisms: Seat-Valve (spherical, hard, flat), Log-Valve (plunger, spring, rotating disk).

7.2. Switching Valves

Control the passage of air. Types:

  • 2-way 2-position valve (on/off)
  • Quick Exhaust (speeds up cylinder retraction)
  • AND/OR selectors

7.3. Flow and Pressure Control Valves

Regulate flow rate and limit pressure.

  • Flow Regulator: Adjusts airflow (unidirectional or bidirectional).
  • Pressure Regulator: Maintains constant pressure at the output and in the maintenance unit.
  • Safety/Overpressure Valve: Prevents pressure from exceeding a set value.
  • Sequence Valve: Similar to safety valve, but output opens only when a higher pressure is reached.

7.4. Proportional Valves

Continuously regulate output pressure based on an electrical signal.