CHAPTER 11PNEUMATICSThe word pneumatics is a derivative of theGreek word pneuma, which means air, wind, orbreath. It can be defined as that branch ofengineering science that pertains to gaseouspressure and flow. As used in this manual,pneumatics is the portion of fluid power in whichcompressed air, or other gas, is used to transmitand control power to actuating mechanisms.This chapter discusses the origin of pneu-matics. It discusses the characteristics of gases andcompares them with those of liquids. It alsoexplains factors which affect the properties ofgases, identifies and explains the gas laws, andidentifies gases commonly used in pneumatics andtheir pressure ranges. It also discusses hazards ofpneumatic gases, methods of controlling contami-nation, and safety precautions associated withcompressed gases.DEVELOPMENT OF PNEUMATICSThere is no record of man’s first uses of airto do work. Probably the earliest uses were toseparate chaff from grain and to move ships. Oneof the first pneumatic devices was the blow gunused by primitive man. In the latter part of theeighteenth century, heated air was used to carrythe first balloon aloft. The heated air, beinglighter than the surrounding air, caused theballoon to rise.Every age of man has witnessed the develop-ment of devices which used air to do work.However, man used air to do work long beforehe understood it.Many of the principles of hydraulics apply topneumatics. For example, Pascal’s law applies togases as well as liquids. Also, like hydraulics, thedevelopment of pneumatics depended on closelyfitted parts and the development of gaskets andpackings. Since the invention of the air com-pressor, pneumatics has become a very reliableway to transmit power.Probably one of the most common uses ofpneumatic power is in the operation of pneumatictools. However, you should understand thatpneumatics is also of great importance in largeand complex systems such as the controls of vitalpropulsion and weapon systems.CHARACTERISTICS OF GASESRecall from chapter 1 that gas is one of thethree states of matter. It has characteristics similarto those of liquids in that it has no definite shapebut conforms to the shape of its container andreadily transmits pressure.Gases differ from liquids in that they have nodefinite volume. That is, regardless of the size orshape of the containing vessel, a gas willcompletely fill it. Gases are highly compressible,while liquids are only slightly so. Also, gases arelighter than equal volumes of liquids, makinggases less dense than liquids.DENSITYEarly experiments were conducted concerningthe behavior of air and similar gases. Theseexperiments were conducted by scientists such asBoyle and Charles (discussed later in this chapter).The results of their experiments indicated that thegases’ behavior follows the law known as theideal-gas law. It states as follows: For a givenweight of any gas, the product of the absolutepressure and the volume occupied, divided by theabsolute temperature, is constant. In equationform, it is expressed as follows:Equation 11-1For 1 pound of gas,Equation 11-211-1
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business