CHAPTER 11 PNEUMATICS 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  manual, 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  chapter  discusses  the  origin  of  pneu- matics. It discusses the characteristics of gases and compares   them   with   those   of   liquids.   It   also explains  factors  which  affect  the  properties  of gases,  identifies  and  explains  the  gas  laws,  and identifies  gases  commonly  used  in  pneumatics  and their pressure ranges. It also discusses hazards of pneumatic gases, methods of controlling contami- nation,  and  safety  precautions  associated  with compressed  gases. DEVELOPMENT  OF  PNEUMATICS There  is  no  record  of  man’s  first  uses  of  air to  do  work.  Probably  the  earliest  uses  were  to separate chaff from grain and to move ships. One of the first pneumatic devices was the blow gun used by primitive man. In the latter part of the eighteenth century, heated air was used to carry the   first   balloon   aloft.   The   heated   air,   being lighter   than   the   surrounding   air,   caused   the balloon  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  before he  understood  it. Many of the principles of hydraulics apply to pneumatics. For example, Pascal’s law applies to gases as well as liquids. Also, like hydraulics, the development  of  pneumatics  depended  on  closely fitted parts and the development of gaskets and packings.  Since  the  invention  of  the  air  com- pressor,  pneumatics  has  become  a  very  reliable way  to  transmit  power. Probably  one  of  the  most  common  uses  of pneumatic power is in the operation of pneumatic tools.  However,  you  should  understand  that pneumatics  is  also  of  great  importance  in  large and complex systems such as the controls of vital propulsion  and  weapon  systems. CHARACTERISTICS  OF  GASES Recall  from  chapter  1  that  gas  is  one  of  the three states of matter. It has characteristics similar to those of liquids in that it has no definite shape but  conforms  to  the  shape  of  its  container  and readily transmits pressure. Gases differ from liquids in that they have no definite volume. That is, regardless of the size or shape  of  the  containing  vessel,  a  gas  will completely fill it. Gases are highly compressible, while liquids are only slightly so. Also, gases are lighter  than  equal  volumes  of  liquids,  making gases less dense than liquids. DENSITY Early  experiments  were  conducted  concerning the   behavior   of   air   and   similar   gases.   These experiments were conducted by scientists such as Boyle and Charles (discussed later in this chapter). The results of their experiments indicated that the gases’  behavior  follows  the  law  known  as  the ideal-gas  law.  It  states  as  follows:  For  a  given weight  of  any  gas,  the  product  of  the  absolute pressure and the volume occupied, divided by the absolute  temperature,  is  constant.  In   equation form,  it  is  expressed  as  follows: Equation 11-1 For  1  pound  of  gas, Equation  11-2 11-1