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Fluid Power Systems
Control

Fluid Power - Intro to Hydraulics, Pneumatics, and how it all works
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rise  to  a  predetermined  pressure,  the  valve automatically  returns  to  the  neutral  position  and, consequently,  to  open-center  flow. One  of  the  advantages  of  the  open-center system is that the continuous pressurization of the system  is  eliminated.  Since  the  pressure  is gradually  built  up  after  the  directional  control valve is moved to an operating position, there is very  little  shock  from  pressure  surges.  This provides  a  smooth  operation  of  the  actuating mechanisms;  however,  the  operation  is  slower than the closed-center system in which the pressure is  available  the  moment  the  directional  control valve   is   positioned.   Since   most   applications require   instantaneous   operation,   closed-center systems are the most widely used. HYDRAULIC  POWER  DRIVE  SYSTEM The  hydraulic  power  drive  has  been  used in   the   Navy   for   many   years.   Proof   of   its effectiveness is that it has been used to train and elevate  nearly  all  caliber  guns,  from  the  40-mm gun  mount  to  the  16-inch  turret.  In  addition  to gun mounts and turrets, hydraulic power drives are  used  to  position  rocket  launchers  and missile launchers, and to drive and control such equipment as windlasses, capstans, and winches. In  its  simplest  form,  the  hydraulic  power  drive consists  of  the  following: 1.  The  prime  mover,  which  is  the  outside source of power used to drive the hydraulic pump 2.  A  variable-displacement  hydraulic  pump 3.  A  hydraulic  motor 4.  A  means  of  introducing  a  signal  to  the hydraulic  pump  to  control  its  output 5.  Mechanical  shafting  and  gearing  that transmits  the  output  of  the  hydraulic  motor  to  the equipment  being  operated Hydraulic   power   drives   differ   in   some respects, such as size, method of control, and so forth.   However,   the   fundamental   operating principles  are  similar.  The  unit  used  in  the following   discussion   of   fundamental   operating principles  is  representative  of  the  hydraulic  power drives  used  to  operate  the  5"/38  twin  mounts. Figure  12-5  shows  the  basic  components  of the  train  power  drive.  The  electric  motor  is constructed  with  drive  shafts  at  both  ends.  The forward  shaft  drives  the  A-end  pump  through reduction  gears,  and  the  after  shaft  drives  the auxiliary pumps through the auxiliary reduction gears. The reduction gears are installed because Figure 12-5.-Train power drive—components.







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