Fluid Power Systems: Pneumatic and Hydraulic Control Technology

Fundamentals of Pneumatic and Hydraulic Control

Pneumatic and hydraulic systems utilize different mediums for control:

• Electric Control: Uses electrical signals.
• Pneumatic Control: Uses air pressure (a gas).
• Hydraulic Control: Uses liquid (typically oil).

Characteristics of Working Fluids

The primary characteristics defining fluid behavior in these systems are pressure and flow.

Note on Fluid Characteristics: Pressure ($P$) and Flow ($Q$) are defined by fundamental physics principles:

• $P = F / S$ (Pressure equals Force divided by Surface Area)
• $Q = V / T = S \times \text{displacement} / T$ (Flow rate equals Volume divided by Time)

Components of a Pneumatic System Installation

A complete pneumatic installation includes:

• Compressor and tank (storage)
• Conditioning units (treatment)
• Pipes and accessories (transport and distribution)

Treatment and Conditioning of Compressed Air

Proper air treatment is crucial for system longevity and performance. This process involves three main steps:

1. Filtration: Removing impurities.
2. Pressure Regulation: Maintaining stable pressure.
3. Lubrication: Adding oil mist to reduce friction.

Compressed Air Distribution Network

The distribution network consists of the piping system that transports the treated air to the points of use.

Advantages of Pneumatic Systems

Pneumatic systems offer several benefits, making them suitable for various industrial environments:

• They avoid explosions in industries where explosive atmospheres may exist.
• They are suitable for places with moist environments.
• Pneumatic energy is easy to transform into other types of energy.

Benefits of Compressed Air

Furthermore, compressed air:

• Is obtained easily.
• Moves quickly through pipes.
• Is easy to store.
• Is a clean system.

Sample Applications of Pneumatic Systems

Common applications include:

• Cleanup operations.
• Operating train doors.
• Industrial automation tasks.

System Components and Functions

Pneumatic and hydraulic systems are typically divided into five functional groups:

1. Production and Storage

   The compressor generates compressed air. The accumulator (tank) stores the air.

2. Treatment, Conditioning, and Measurement

   Includes filters, regulators, lubricators, and various measurement accessories.

3. Transport Elements

   Consists of plastic or metal pipes.

4. Control and Distribution Elements

   Includes valves and distributor control valves used to direct and regulate fluid flow.

5. Actuator Elements

   These elements convert fluid energy into mechanical motion:

   • Cylinders: Provide linear displacement.
   • Motors: Provide relative motion (continuous rotation).
   • Actuators: Generate angular rotation of a shaft.

Air Compression and Treatment Details

Production and Treatment of Compressed Air

The compressor increases the pressure of the intake air.

Types of Air Compressors

Compressors are generally categorized into two types:

• Volumetric (Positive Displacement): Reduce the volume of air to increase pressure.
• Dynamic (Turbocharging): Increase the speed of the intake air, driven by rotating parts, converting kinetic energy into pressure.

Detailed Air Treatment Requirements

Air treatment must ensure the air is clean, lubricated, and regulated.

Filters: Removing Impurities

Filters remove impurities that can cause errors in circuits, such as wear on components or valves failing to move correctly, and prevent excess water concentration. Filters are typically placed downstream of compressors and tanks.

Lubricators: Reducing Friction

The purpose of lubrication is the reduction of friction between moving elements. A lubricator introduces oil drop by drop into the air stream.

Pressure Regulators: Ensuring Stability

Regulators are used to avoid pressure variations in the circuit. Achieving stable pressure results in:

• Better performance.
• Prevention of excessive wear on elements.
• Avoidance of unnecessary air consumption.

Control Valves in Pneumatic Circuits

Valves are essential pneumatic circuit elements. They allow air to pass when necessary and direct the air flow where desired.

Valve Structure and Identification

A valve consists of a housing containing a movable element that shifts between specific positions. It has defined inputs and outputs. Valves are identified by the number of routes (ports) and positions they possess.

Valve Components

Key components include:

• Actuator Mechanism: Initiates the movement of the mobile device.
• Mobile Device: The internal element that controls flow.
• Return Mechanism: Returns the valve to its rest position (e.g., a spring).

Hydraulic Systems: Characteristics and Differences

In hydraulic systems, the working fluid is a liquid, typically oil. The fundamental elements are the same as those in pneumatic circuits, but they are constructed robustly to withstand significantly higher pressures.

Advantages of Hydraulic Systems

Hydraulic systems offer superior performance in high-power applications:

• They transmit more power.
• It is easier to regulate the speed of actuators precisely.
• Cylinders can be stopped and held accurately at any position.

Disadvantages of Hydraulic Systems

Despite their power, hydraulic systems have drawbacks:

• They require return pipes and an oil reservoir (deposit).
• They have a higher initial cost.
• The overall system complexity is greater.