INTRODUCTION
Hydraulics has proven to be the most efficient and economical system adaptable to aviation. First used by the ancient Greeks as a means of elevating the stages of their amphitheaters, the principles of hydraulics were explained scientifically by the seventeenth century scholars Pascal and Boyle. The laws discovered by these two men regarding the effects of pressure and temperature on fluids and gases in confined areas form the basis of the principle of mechanical advantage; in other words, the "why and how" of hydraulics.
This chapter explains to you the basic applications of hydraulics in Army aviation and the characteristics of these systems. The explanations include detailed definitions of the terminology peculiar to hydraulics with which you must be familiar to fully understand this subject.
In aviation, hydraulics is the use of fluids under pressure to transmit force developed in one location on an aircraft or other related equipment to some other point on the same aircraft or equipment. Hydraulics also includes the principles underlying hydraulic action and the methods, fluids, and equipment used in implementing those principles.
In aviation, hydraulics is the use of fluids under pressure to transmit force developed in one location on an aircraft or other related equipment to some other point on the same aircraft or equipment. Hydraulics also includes the principles underlying hydraulic action and the methods, fluids, and equipment used in implementing those principles.
HYDRAULIC AND HYDRAULICS
The word "hydraulic" is derived from two Greek words: "hydro" meaning liquid or water and "aulos" meaning pipe or tubing. "Hydraulic," therefore, is an adjective implying that the word it modifies is in some major way concerned with liquids. Examples can be found in the everyday usage of "hydraulic" in connection with familiar items such as automobile jacks and brakes. As a further example, the phrase "hydraulic freight elevator" refers to an elevator ascending and descending on a column of liquid instead of using cables and a drum.
Hydraulic systems are widely used in various applications, from heavy machinery and industrial equipment to aircraft and automotive systems. They work by using fluid under pressure to generate, control, and transmit power, making them capable of handling large forces with precision and efficiency. Here’s a look at the basics of hydraulic systems, including their components, principles, and common applications.
Basics of Hydraulic Systems
1. Fundamental Principle: Pascal’s Law
- Hydraulic systems operate based on Pascal’s Law, which states that pressure exerted on a confined fluid is transmitted equally in all directions. This principle allows hydraulic systems to amplify force, enabling the movement and control of large loads with minimal input force. By using incompressible fluids, such as oil, hydraulic systems can deliver consistent power and motion.
2. Main Components of Hydraulic Systems
- Hydraulic Pump: Converts mechanical energy into hydraulic energy by moving hydraulic fluid from the reservoir to the rest of the system. Pumps are typically driven by electric motors or engines and can be gear pumps, vane pumps, or piston pumps.
- Reservoir: Stores hydraulic fluid and supplies it to the pump. The reservoir also helps cool the fluid, allows contaminants to settle, and keeps air out of the system.
- Hydraulic Fluid: The medium that transmits power. Hydraulic fluid also lubricates, cools, and reduces wear on the components. Oil is commonly used due to its stability, but other fluids may be used based on application needs.
- Actuators: Convert hydraulic energy back into mechanical energy to perform work. Actuators include:
- Cylinders: Produce linear motion to push, pull, or lift loads.
- Hydraulic Motors: Produce rotary motion for driving wheels, gears, or other rotating elements.
- Valves: Control the flow, direction, and pressure of the hydraulic fluid within the system. They include control valves, check valves, and pressure relief valves.
- Filters: Remove contaminants from the hydraulic fluid, ensuring that the system operates smoothly without wear or damage to sensitive components.
- Piping and Hoses: Carry the hydraulic fluid between the components. These conduits must be strong enough to handle high pressures without leaks or bursts.
3. Operating Principles
- In a hydraulic system, the pump pressurizes the hydraulic fluid, which is then directed to an actuator through a series of valves. When the fluid reaches the actuator, it exerts a force that produces movement or work. By controlling the fluid’s flow, direction, and pressure, operators can precisely manage the force and speed of the actuators.
- Hydraulic systems are typically closed-loop or open-loop:
- Closed-loop systems recirculate fluid continuously and are often used in applications that require consistent control, such as servo systems.
- Open-loop systems draw fluid from the reservoir only as needed and are common in simpler applications.
4. Advantages of Hydraulic Systems
- High Power Density: Hydraulics can produce very high forces and torque, making them ideal for heavy-duty applications.
- Precision and Control: Hydraulic systems allow fine control over speed, force, and direction, useful in applications that require precision.
- Flexibility and Versatility: The same system can control various movements—linear or rotary—by using different actuators.
- Durability and Reliability: Hydraulic systems are generally robust, withstanding harsh operating environments with proper maintenance.
5. Common Applications
- Construction and Agricultural Equipment: Excavators, bulldozers, tractors, and other heavy machinery rely on hydraulics to move large loads and perform earthmoving tasks.
- Industrial Machinery: Many machines in manufacturing, such as presses and injection molding machines, use hydraulics for precise, high-force operations.
- Automotive Braking Systems: Hydraulic brakes use fluid to transfer force from the brake pedal to the brakes, offering precise control and stopping power.
- Aircraft Systems: Hydraulics are used in flight control systems, landing gear, and braking systems due to their reliability and power.
- Marine and Offshore Equipment: Winches, cranes, and stabilizers on ships and offshore rigs use hydraulic systems to handle heavy loads under variable conditions.
6. Basic Maintenance of Hydraulic Systems
- Fluid Maintenance: Regularly checking fluid levels and quality is essential. Hydraulic fluid should be replaced when contaminated or degraded.
- Filter Replacement: Filters need to be cleaned or replaced regularly to prevent contaminants from entering the system.
- Leak Detection: Checking for leaks is crucial to avoid loss of pressure, contamination, and system failure.
- Inspection of Components: Hoses, seals, and other components should be inspected for wear or damage and replaced as needed.
7. Safety Considerations
- High-pressure systems can be dangerous, so proper safety practices are essential, including wearing personal protective equipment (PPE), releasing pressure safely before maintenance, and avoiding contact with high-pressure leaks that can cause injury.
Summary
Hydraulic systems are a powerful and versatile technology widely used across various industries due to their ability to generate significant force and precise control. By leveraging the principles of fluid mechanics, they can handle heavy-duty applications that require durability and reliability. Proper maintenance is essential to keep these systems operating effectively, ensuring safety, performance, and longevity.
