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Mixed-Bed   Cartridge
LIQUID-COOLING   SYSTEM   ALARM SWITCHBOARDS

Fire Controlman Volume 04-Fire Control Maintenance Concepts
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The  purity  meter  indication  varies  with  ionized salt  concentration  and  the  temperature  of  the  coolant flowing   through   the   cell.   The   temperature   effect   is canceled  by  a  built-in  temperature  compensation  cir- cuit. The  inlet  conductivity  is  compared  to  a  preset value  of  cell  conductance  to  actuate  an  alarm  circuit when  the  purity  of  the  water  drops  below  the  preset level.  In  addition,  the  purity  meter  provides  direct readings  of  the  water  purity  at  the  inlet  and  the  outlet of   the   demineralizer   Typical   operating   requirements for  the  demineralizer  are  conductivity  1  micromho/cm at   77°F   (resistivity   1   megohm/cm   at   77°F),   oxygen content   0.1   parts   per   million   (ppm)   by   weight,   and mechanical   filtration   0.5   microns   absolute. When  water  has  been  circulated  through  the  sys- tem  for  extended  periods  of  time,  a  high-resistivity  or low-conductivity   reading   may   be   indicated   on   both input   and   output   samples.   This   condition   is   highly desirable  and  indicates  that  all  ionizable  material  has been  properly  treated  and  that  the  demineralizer  is maintaining  a  high  degree  of  purity.  When  a  system  is filled  with  a  fresh  charge  of  water,  it  should  be  al- lowed  to  circulate  for  approximately  2  hours  before comparing  the  input  and  output  readings.  During  the initial  circulation  period,  the  resistivity  readings  vary because  of  the  mixing  action  of  water  that  has  been treated  by  the  demineralizer  with  the  fresh  charge  of water. A  properly  operating  system  can  supply  water  of acceptable  purity  in  4  to  8  hours.  Water  in  a  system that  has  been  secured  for  any  length  of  time  should  be of  acceptable  purity  within  2  hours.  The  resistivity  or conductivity   reading   required   for   a   specific   installa- tion  must  be  maintained  for  optimum  operation  of  the cooling   water   system. The  first  indication  of  a  problem  in  the  demineral- izer  is  usually  indicated  by  abnormal  purity  meter readings  (too  low/high),  an  abnormal  flowmeter  read- ing,  and/or  alight  and  audible  warning  from  the  purity monitor.  Some  purity  monitors  can  be  tested  for accuracy  by  a  built-in  test  function  on  the  meter  to establish  if  the  problem  is  in  the  purity  monitor.  If  the purity  monitor  does  not  have  a  test  feature,  then  use the  calibration  plug  in  place  of  one  of  the  conductivity cells  to  test  the  operation  of  the  purity  meter.  Most  of the  time,  only  routine  maintenance  is  required  to  re- turn  the  demineralizer  to  its  normal  operating  condi- tion. Maintenance   of   the   demineralizer   consists   pri- marily   of   the   scheduled   replacement   of   cartridges (before   they   are   exhausted)   and   clogged   filters. Obtaining  satisfactory  service  life  from  the  cartridges and  filters  is  largely  dependent  on  minimizing  ex- ternal  contamination.  Replacement  cartridges  must  be kept  sealed  and  stored  in  a  cool,  dry  place  until  used. The  circulating  system  must  be  kept  tight  to  reduce the  need  for  makeup  water.  Makeup  water,  in  any case,  should  be  as  particle-free  as  possible  and  should not  exceed  0.065  ppm  chloride. OXYGEN   ANALYZERS Oxygen  analyzers  are  installed  in  some  secondary cooling  systems  to  measure  the  amount  of  dissolved oxygen  in  the  liquid  coolant.  The  presence  of  oxygen causes  oxidation  that  leads  to  the  formation  of  scale  in the  cooling  system.  An  oxygen  analyzer  has  an  oxy- gen  sensor  installed  in  the  supply  side  of  the  second- ary  cooling  system. The  sensor  is  an  electrolytic  cell  in  an  electrolyte solution  or  gel.  The  oxygen  reacts  with  the  electrolyte, causing  a  proportional  change  in  the  amount  of  cur- rent  flow  in  the  sensor.  The  sensor’s  electrical  output is  measured  and  displayed  on  the  oxygen  analyzer’s meter,  which  is  calibrated  to  read  the  oxygen  content in  parts  per  million  or  billion. Because  of  the  solid-state  electronics  and  the  few components   used,   the   oxygen   analyzer   requires   very little   maintenance   other   than   cleaning   and   changing the  electrolyte  in  the  sensor.  When  the  meter  on  the analyzer   requires   frequent   calibration   because   the meter   readings   are   drifting   or   changing   sharply,   the analyzer  has  a  bad  sensor. 2-23






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