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Chapter 9 Reservoirs, Strainers, Filters and Accumulators
Accumulators

Fluid Power - Intro to Hydraulics, Pneumatics, and how it all works
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installations.  A  typical  reservoir  for  use  with ground and ship installations is shown in figure 9-1.  This  type  of  reservoir  is  made  of  hot  rolled steel  plates  and  has  welded  seams.  The  ends  extend below  the  bottom  of  the  reservoir  and  serve  as supports. The bottom of the reservoir is convex, and  a  drain  plug  is  incorporated  at  the  lowest point. Nonpressurized  reservoirs  are  also  used  in several  transport-, patrol-,   and   utility-type aircraft.  These  aircraft  are  not  designed  for  violent maneuvers and, in some cases, do not fly at high altitude. Those aircraft that have nonpressurized reservoirs installed and that fly at high altitudes have the reservoirs installed within a pressurized area.  (High  altitude  in  this  situation  means  an altitude  where  atmospheric  pressure  is  inadequate to  maintain  sufficient  flow  of  fluid  to  the hydraulic   pumps.) Most  nonpressurized  aircraft  reservoirs  are constructed  in  a  cylindrical  shape  (fig.  9-2).  The outer  housing  is  manufactured  from  a  strong corrosion-resistant   metal.   Filter   elements   are normally installed internally within the reservoir to  clean  returning  system  hydraulic  fluid.  Some of  the  older  aircraft  have  a  filter  bypass  valve installed to allow fluid to bypass the filter if the filter becomes clogged. Reservoirs that are filled by  pouring  fluid  directly  into  them  have  a  filler (finger) strainer assembly installed in the filler well to  strain  out  impurities  as  the  fluid  enters  the reservoir. Figure 9-2.—Nonpressurized aircraft reservoir. The  quantity  of  fluid  in  the  reservoir  is indicated by either a glass tube, a directing gauge, or  a  float-type  rod,  which  is  visible  through  a transparent  dome  installed  on  the  reservoir. PRESSURIZED RESERVOIRS A pressurized reservoir is required in hydraulic systems  where  atmospheric  pressure  is  insufficient to maintain a net positive suction head (NPSH) to  the  pump.  There  are  two  common  types  of pressurized  reservoirs—fluid-pressurized  and air-pressurized. Fluid-Pressurized  Reservoir Some   aircraft   hydraulic   systems   use   fluid pressure  for  pressurizing  the  reservoir.  The reservoir shown in figure 9-3 is of this type. This reservoir  is  divided  into  two  chambers  by  a floating  piston.  The  piston  is  forced  downward in  the  reservoir  by  a  compression  spring  within the pressurizing cylinder and by system pressure entering  the  pressurizing  port  of  the  cylinder. The pressurizing port is connected directly to the pressure line. When the system is pressurized, pressure  enters  the  pressure  port,  thus  pressurizing the reservoir. This pressurizes the pump suction line  and  the  reservoir  return  line  to  the  same pressure. The  reservoir  shown  in  figure  9-3  has  five ports—pump   suction,   return,   pressurizing, overboard drain, and bleed. Fluid is supplied to the pump through the pump suction port. Fluid returns to the reservoir from the system through the return port. Pressure from the pump enters the pressurizing cylinder in the top of the reservoir through  the  pressurizing  port.  The  overboard drain  port  is  used  to  drain  the  reservoir  while performing  maintenance,  and  the  bleed  port  is used as an aid when servicing the reservoir. Air-Pressurized  Reservoirs Air-pressurized  reservoirs,  such  as  the  one shown in figure 9-4, are currently used in many high-performance naval aircraft. The reservoir is cylindrical  in  shape  and  has  a  piston  installed internally  to  separate  the  air  and  fluid  chambers. Air pressure is usually provided by engine bleed air.  The  piston  rod  end  protrudes  through  the reservoir  end  cap  and  indicates  the  fluid  quantity. The quantity indication may be seen by inspecting the  distance  the  piston  rod  protrudes  from  the reservoir end cap. The reservoir is provided with 9-2







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