Page 21 - Reciprocating Compressors Operation Maintenance
P. 21

8   Reciprocating  Compressors:  Operation and Maintenance


                               Compressors
                      Dynamic     I     Displacement



               Ejector   Radial    Axial






                     Rotary                         Reciprocating











                 FIGURE   1 -5.  Principal compressor types used in industry.


             Positive  displacement  units are  those in  which successive  volumes
             of  gas  are  confined within a  closed  space  and  elevated  to  a higher
             pressure.
             Rotary  positive  displacement  compressors  are  machines  in which
             compression  and  displacement  result  from  the  positive  action  of
             rotating elements.
             Sliding  vane  compressors  are rotary  positive  displacement
             machines in  which axial vanes slide  radially in a rotor  eccentrically
             mounted  in a cylindrical casing. Gas trapped between  vanes is com-
             pressed  and displaced.
             Liquid  piston  compressors  are  rotary positive  displacement
             machines in which water or other liquid is used as the piston  to com-
             press and displace the gas handled.
             Two-impeller  straight-lobe  compressors  are  rotary  positive  dis-
             placement  machines in  which two  straight  mating lobed  impellers
             trap  gas  and  carry it  from  intake to  discharge.  There  is  no internal
             compression.
             Helical  or spiral  lobe  compressors  are rotary positive  displacement
             machines in which two intermeshing rotors,  each with a helical form,
             compress and displace the gas.
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