Catalog of Skilled-Trade Learning Resources
Fluid Power

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I am pleased to offer this course of study for the theory and practice of modern fluid power -- hydraulics and pneumatics. These lessons are generic in the sense that there is no particular bias for any specific application. The level of presentation is suitable for 4-year apprenticeship programs.


Study Topics for

This short lesson that introduces fluid power as hydraulics and pneumatics.

The study of liquids is divided into two main parts: liquids at rest (hydrostatics) and liquids in motion (hydraulics). The effects of liquids at rest can often be expressed by simple formulas. The effects of liquids in motion, on the other hand, are more difficult to express due to frictional and other factors whose actions cannot be expressed by simple mathematics.

This lesson is devoted to hydraulic fluids. Included in it are sections on the properties and characteristics desired of hydraulic fluids; types of hydraulic fluids; hazards and safety precautions for working with, handling, and disposing of hydraulic liquids; types and control of contamination; and sampling.

The purpose of a hydraulic pump is to supply a flow of fluid to a hydraulic system. The pump does not create system pressure, since pressure can be created only by a resistance to the flow. As the pump provides flow, it transmits a force to the fluid. As the fluid flow encounters resistance, this force is changed into a pressure.

Fluid power is a term that describes the generation, control, and application of smooth, effective power of pumped or compressed fluids (either liquids or gases) to provide force and motion to mechanisms. This force and motion may be in the form of pushing, pulling, rotating, regulating, or driving. Fluid power includes hydraulics and pneumatics, which involve liquids and gases, respectively.

It is all but impossible to design a practical fluid power system without some means of controlling the volume and pressure of the fluid and directing the flow of fluid to the operating units. This is accomplished by the incorporation of different types of valves. A valve is defined as any device by which the flow of fluid may be started, stopped, or regulated by a movable part that opens or obstructs passage. As applied in fluid power systems, valves are used for controlling the flow, the pressure, and the direction of the fluid flow. Valves must be accurate in the control of fluid flow and pressure and the sequence of operation.

This lesson deals primarily with the different types of materials used in the construction of seals. You will also learn about the different shapes and designs of seals and their application as gaskets and/or packings in fluid power systems. Finally you will find sections concerning the functions of wipers and scrapers in fluid power systems and the selection, storage, and handling of sealing devices.

For safe and efficient operation, fluid power systems are designed to operate at a specific pressure and/or temperature, or within a pressure and/or temperature range. Most fluid power systems are provided with pressure gauges and thermometers for measuring and indicating the pressure and/or the temperature in the system. Additionally, various temperature and pressure switches are used to warn of an adverse pressure or temperature condition. Some switches will even shut the system off when an adverse condition occurs. These devices will be discussed in this lesson.

Fluid power systems must have a sufficient and continuous supply of uncontaminated fluid to operate efficiently. This lesson covers hydraulic reservoirs, various types of strainers and filters, and accumulators installed in fluid power systems.

One of the outstanding features of fluid power systems is that force, generated by the power supply, controlled and directed by suitable valving, and transported by lines, can be converted with ease to almost any kind of mechanical motion desired at the very place it is needed. Either linear (straight line) or rotary motion can be obtained by using a suitable actuating device. This lesson describes various types of actuating cylinders and their applications, different types of fluid motors, and turbines used in fluid power systems.

The word pneumatics is a derivative of the Greek word pneuma, which means air, wind, or breath. It can be defined as that branch of engineering science that pertains to gaseous pressure and flow. As used in this series of lessons, pneumatics is the portion of fluid power in which compressed air, or other gas, is used to transmit and control power to actuating mechanisms. This series of lessons discuss the basic principles of pneumatics--the characteristics of gases comapred with the characteristics of liquids.


Each lesson concludes with a set of multiple-choice questions. Answers are not provided, however. These are basically "open-book" quizzes, so you should be able to verify your choice of responses by reviewing the text.

Much of the content of this manual is adapted from handbooks prepared by the U.S. Department of Defense. Occasional references of military specifications and protocols do not affect the principles of similar civilian work.

Copyright David L. Heiserman
All Rights Reserved