APPENDIX  I GLOSSARY A part of this glossary has been extracted from the  American  Standard  Glossary  of  Terms  for Fluid Power  (ASA  B93.2-1965)  with  permission of  the  publisher,  The  National  Fluid  Power Association. ABSOLUTE TEMPERATURE—The tempera- ture measured using absolute zero as a reference. Absolute   zero   is   –273.16°C   or   –459.69°F. ACCELERATION—Time   rate   of   change   of velocity. ACCUMULATOR—A   device   for   storing liquid  under  pressure.  It  usually  consists  of  a chamber  separated  into  a  gas  compartment  and a liquid compartment by a piston or diaphragm. An  accumulator  also  serves  to  smooth  out pressure surges in a hydraulic system. ACTUATOR—A   device   that   converts   fluid power  into  mechanical  force  and  motion. ADDITIVE—A   chemical   compound   or compounds  added  to  a  fluid  to  change  its properties. AIR,   COMPRESSED—Air   at   any   pressure greater than atmospheric pressure. AMBIENT—Surrounding,   such   as   ambient air,  meaning  surrounding  air. BAROMETER—An   instrument   that   mea- sures atmospheric pressure. BERNOULLI’S   PRINCIPLE—If   a   fluid flowing through a tube reaches a constriction, or narrowing  of  the  tube,  the  velocity  of  the  fluid flowing  through  the  constriction  increases  and  the pressure decreases. BLEEDER,  AIR—A  bleeder  for  the  removal of  air. BOYLE’S  LAW—The  absolute  pressure  of  a fixed mass of gas varies inversely as the volume, provided  the  temperature  remains  constant. CAVITATION—A    localized    gaseous condition  within  a  liquid  stream  that  occurs  where the  pressure  is  reduced  to  the  vapor  pressure. CELSIUS—The  temperature  scale  using  the freezing  point  of  water  as  zero  and  the  boiling point  as  100,  with  100  equal  divisions  between, called degrees. This scale was formerly known as the centigrade scale. CENTIGRADE—(See  Celsius.) CENTRIFUGAL  FORCE—A  force  exerted on a rotating object in a direction outward from the  center  of  rotation. CHARLES’S   LAW—If   the   pressure   is constant,  the  volume  of  dry  gas  varies  directly with  the  absolute  temperature. CHEMICAL   CHANGE—A   change   that alters   the   composition   of   the   molecules   of   a substance. CIRCUIT—An  arrangement  of  intercon- nected  component  parts. COMPRESSIBILITY—The change in volume of  a  unit  volume  of  a  fluid  when  it  is  subjected to  a  unit  change  of  pressure. COMPRESSOR—A   device   that   converts mechanical force and motion into pneumatic fluid power. COMPUTER—A  device  capable  of  accepting information, applying prescribed processes to the information,  and  supplying  the  results  of  these processes. AI-1