Fluid Power Systems: Components, Principles, & Applications

Hydraulic Power Unit Components & Functions

A hydraulic power unit is the assembly that provides power to the fluid to operate a hydraulic circuit. It typically consists of the following essential elements:

• Pump: Generates fluid flow.
• Tank: Stores hydraulic fluid.
• Relief Valve: Protects the system from overpressure.
• Actuator: Converts hydraulic energy into mechanical motion.
• Selector Valve: Directs fluid flow to different parts of the circuit.
• Anti-return Valve: Prevents backflow of fluid.

Mobile vs. Fixed Hydraulic Power Units

The distinction between mobile and fixed hydraulic power units lies primarily in their application and portability:

• Mobile Hydraulic Power Units: These systems are designed for applications where the power unit is not stationary. They are commonly found in equipment such as tractors, cranes, trucks, and automobile braking systems. Their mobility allows for versatile use in various dynamic environments.
• Fixed Hydraulic Power Units: In contrast, fixed hydraulic power units are larger, stationary assemblies with a dedicated, permanent location. They are extensively used in industrial settings for heavy machinery, machine tools, robots, assembly equipment, and automation processes, providing consistent and robust power.

Role of Directional Valves in Air/Oil Systems

In an air/oil system, the directional valve plays a crucial role by determining the direction of fluid flow. This, in turn, dictates the direction of operation for the actuator, enabling precise control over mechanical movements.

Understanding Hydraulic Accumulators

Hydraulic accumulators are devices designed to store hydraulic fluid under pressure. They serve a range of functions within a hydraulic system, including energy storage, shock absorption, and pressure compensation. A common application is in a hydraulic jack, where the accumulator builds up and maintains pressure as the lever is operated, preventing pressure escape and ensuring efficient lifting.

Compressed Air Treatment Process

The treatment of compressed air is vital for the longevity and efficiency of pneumatic components. This process primarily involves drying and filtering the compressed air.

Methods of Compressed Air Drying:

• Absorption: Uses chemical desiccants to absorb moisture.
• Adsorption: Employs desiccant materials to adsorb water vapor.
• Cooling: Lowers the air temperature to condense and remove moisture.

After drying and initial filtration, compressed air passes through an FRL unit (Filter, Regulator, Lubricator). This unit is strategically placed before the compressed air enters actuators, valves, and hoses. The FRL unit ensures that the air is clean, at the correct pressure, and adequately lubricated, as impurities in compressed air are a significant factor in reducing the lifespan of pneumatic components.

Sliding Vane vs. Turbo Compressors

The fundamental difference between a sliding vane compressor and a turbo compressor lies in their respective mechanisms for compressing air:

• Sliding Vane Compressor: This type of compressor achieves air compression by reducing the area through which the air passes, using a series of vanes that slide in and out of a rotor.
• Turbo Compressor: A turbo compressor, conversely, utilizes a shaft equipped with propellers (impellers), typically divided into multiple sections. It compresses air dynamically by accelerating it and then diffusing it to convert velocity into pressure, similar to the operation of an aircraft turbine.

Essential Properties of Hydraulic & Pneumatic Fluids

Working fluids used in both pneumatic and hydraulic power systems must possess specific characteristics to ensure optimal performance, reliability, and system longevity. These critical properties include:

1. Excellent Lubrication and Wear Protection: To minimize friction and wear on system components.
2. Good Viscosity Index: To maintain stable viscosity across varying temperatures.
3. Compatibility with System Materials: Ensuring no adverse reactions with metals, seals, and other components.
4. Resistance to Thermal Loads: Capable of operating effectively without degradation, typically not exceeding 80°C.
5. Oxidation Resistance: To prevent degradation and sludge formation due to reaction with oxygen.
6. Reduced Foaming Tendency: To prevent air entrapment, which can lead to cavitation and inefficient operation.
7. Easy Heat Dissipation: To help manage system temperature and prevent overheating.
8. Dielectric Properties: For certain applications, the ability to resist electrical conductivity.
9. Non-toxic: Both as a fluid and if it degrades into a gas, for safety and environmental reasons.
10. Non-hygroscopic: To resist absorbing moisture, which can degrade fluid properties and cause corrosion.
11. Non-flammable: A crucial safety property, especially in high-pressure systems.
12. Anticorrosive and Pollution Control: To protect internal components from rust and minimize environmental impact.
13. No Sludge Formation: To maintain system cleanliness and prevent blockages.
14. Good Filterability and Ease of Maintenance: Allowing for effective filtration and simplifying system upkeep.
15. Favorable Cost and Availability: Practical considerations for widespread use and economic viability.