Fluid power is a term which was created to include the generation, control, and application of smooth, effective power of pumped or compressed fluids (either liquids or gases) when this power is used to provide force and motion to mechanisms. This force and motion maybe in the form of pushing, pulling, rotating, regulating, or driving. Fluid power includes hydraulics, which involves liquids, and pneumatics, which involves gases. Liquids and gases are similar in many respects. The differences are pointed out in the appropriate areas of this manual.

This manual presents many of the fundamental concepts in the fields of hydraulics and pneumatics. It is intended as a basic reference for all personnel of the Navy whose duties and responsibilities require them to have a knowledge of the fundamentals of fluid power. Consequently, emphasis is placed primarily on the theory of operation of typical fluid power systems and components that have applications in naval equipment. Many applications of fluid power are presented in this manual to illustrate the functions and operation of different systems and components. However, these are only representative of the many applications of fluid power in naval equipment. Individual training manuals for each rate provide information concerning the application of fluid power to specific equipment for which the rating is responsible.

A brief summary of the contents of this training manual is given in the following paragraphs:

Chapter 2 covers the characteristics of liquids and the factors affecting them. It also explains the behavior of liquids at rest, identifies the characteristics of liquids in motion, and explains the operation of basic hydraulic components.

Chapter 3 discusses the qualities of fluids acceptable for hydraulic systems and the types of fluids used. Included are sections on safety precautions to follow when handling potentially hazardous fluids, liquid contamination, and control of contaminants.

Chapter 4 covers the hydraulic pump, the component in the hydraulic system which generates the force required for the system to perform its design function. The information provided covers classifications, types, operation, and construction of pumps.

Chapter 5 deals with the piping, tubing and flexible hoses, and connectors used to carry fluids under pressure.

Chapter 6 discusses the classification, types, and operation of valves used in the control of flow, pressure, and direction of fluids.

Chapter 7 covers the types and purposes of sealing devices used in fluid power systems, including the different materials used in their construction. Additionally, the guidelines for selecting, installing, and removing O-rings are included.

Chapter 8 discusses the operation of devices used to measure and regulate the pressure of fluids and to measure the temperature of fluids.

Chapter 9 describes the functions and types of reservoirs, strainers, filters, and accumulators, and their uses in fluid power systems.

Chapter 10 discusses the types and operation of actuators used to transform the energy generated by hydraulic systems into mechanical force and motion.

Chapter 11 deals with pneumatics. It discusses the origin of pneumatics, the characteristics and compressibility of gases, and the most commonly used gases in pneumatic systems. Also, sections are included to cover safety precautions and the potential hazards of compressed gases.

Chapter 12 identifies the types of diagrams encountered in fluid power systems. This chapter also discusses how components of chapters 4, 5, 6, 8, 9, and 10 are combined to form and operate together as a system.

A glossary of terms commonly used in fluid power is provided in appendix I. Appendix II provides symbols used in aeronautical mechanical systems, and appendix III provides symbols used in nonaeronautical mechanical systems. The remainder of chapter 1 is devoted to the advantages and problems of fluid power applications. Included are brief sections on the history, development, and applications of hydraulics, the states of matter.

And The extensive use of hydraulics and pneumatics to transmit power is due to the fact that properly constructed fluid power systems possess a number of favorable characteristics. They eliminate the need for complicated systems of gears, cams, and levers. Motion can be transmitted without the slack inherent in the use of solid machine parts. The fluids used are not subject to breakage as are mechanical parts, and the mechanisms are not subjected to great wear. The different parts of a fluid power system can be conveniently located at widely separated points, since the forces generated are rapidly transmitted over considerable distances with small loss. These forces can be conveyed up and down or around corners with small loss in efficiency and without complicated mechanisms. Very large forces can be controlled by much smaller ones and can be transmitted through comparatively small lines and orifices.

If the system is well adapted to the work it is required to perform, and if it is not misused, it can provide smooth, flexible, uniform action without vibration, and is unaffected by variation of load. In case of an overload, an automatic release of pressure can be guaranteed, so that the system is protected against breakdown or strain. Fluid power systems can provide widely variable motions in both rotary and straight-line trans-mission of power. The need for control by hand can be minimized. In addition, fluid power systems are economical to operate.

The question may arise as to why hydraulics is used in some applications and pneumatics in others. Many factors are considered by the user and/or the manufacturer when determining which type of system to use in a specific application. There are no hard and fast rules to follow; however, past experience has provided some sound ideas that are usually considered when such decisions are made. If the application requires speed, a medium amount of pressure, and only fairly accurate control, a pneumatic system may be used. If the application requires only a medium amount of pressure and a more accurate control, a combination of hydraulics and pneumatics may be used. If the application requires a great amount of pressure and/or extremely accurate control, a hydraulic system should be used.