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HEAT   EXCHANGERS-Cont.
SEAWATER   STRAINERS

Fire Controlman Volume 04-Fire Control Maintenance Concepts
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EXPANSION   TANKS Expansion   tanks   may   be   either   gravity   tanks   or pressurized  tanks.  The  expansion  tank  serves  a  three- fold  purpose  in  a  liquid-cooling  system.  First,  it  main- tains   a   positive   pressure   required   on   the   circulating pump  inlet  for  proper  operation  of  the  circulating pump.  Second,  it  compensates  for  changes  in  the  cool- ant  volume  because  of  temperature  changes.  Third,  it vents  air  from  the  system  and  provides  a  source  of makeup  coolant  to  compensate  for  minor  losses  due  to leakage  or  losses  that  occur  during  the  replacement  of radar  equipment  served  by  the  system.  Refer  to  fig- ures  2-6  and  2-7  as  you  study  this  section. When  an  expansion  tank  is  used  as  a  gravity  tank, it  is  located  above  the  highest  point  in  the  distilled- water  system.  This  provides  sufficient  pressure  to  the suction  side  of  the  circulating  pump.  It  also  ensures  a flow   of   water   from   the   tank   into   the   system   when makeup  water  is  required. The  tank  is  provided  with  a  sight  glass  to  check the  level  of  water  in  the  tank.  The  sight  glass  should normally   show   the   tank   to   be   from   two-thirds   to four-fifths  full.  The  glass  should  be  redlined  at  four- fifths  of  the  tank  capacity.  A  vent  pipe  is  located  on the  top  of  the  tank  to  prevent  air  pressure  from  build- ing  up  in  the  system.  A  valve  and  funnel  connection with a cap are located on the top of the tank to provide a  means  for  filling  the  system  with  distilled  water.  A low-level  alarm  switch  is  usually  set  at  20  percent  of tank   capacity. When  the  fluid  level  in  the  tank  lowers  to  20  per- cent  of  the  full  level,  visual  and  audible  alarms  actuate at  the  alarm  switchboard  to  warn  personnel  that  the system is low on distilled water. If the tank runs out of water,  air  is  drawn  into  the  system,  which  results  in increased  corrective  maintenance  on  the  system  to remove  the  trapped  air  or  possible  pump  damage  and/ or   failure   of   high-power   transmitter   components. The  pressurized  expansion  tank  is  normally  lo- cated  near  the  circulating  pump  suction  in  the  return main   of   the   secondary   liquid-cooling   system.   The pressurized  tank  is  airtight  and  is  charged  with  com- Figure 2-6.—Gravity expansion tank. Figure 2-7.—Pressure expansion tank. 2-9






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