Quantcast Boiler Safety and Water- Pressure  Relief  Valves

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Test  the  freedom  of  each  blowoff  valve  and its  connections  by  opening  the  valve  and  blow- ing  off  the  boiler  for  a  few  seconds.  Determine if  the  valve  is  excessively  worn  or  otherwise defective, and if there is evidence of restrictions in  the  valve  or  connected  piping  preventing proper  blowoff  of  the  boiler. Blowoff Valves be  tested  according  to  the  procedures  given  in paragraph  4  of  this  section. 1.   SAFETY   VALVES—SETTING   RE- QUIREMENTS.  Note  this  word  of  caution: Before adjusting safety valves on electric steam generators, be sure that the electric power circuit to  the  generator  is  open.  The  generator  may  be under steam pressure, but the power line should be  open  while  the  necessary  adjustments  are being made. At least one safety valve should be set  to  release  at  no  more  than  the  maximum allowable  working  pressure  of  the  steam  boiler. Safety valves are factory set and sealed. When a safety valve requires adjustment, the seal should be   broken,   adjustments   made,   and   the   valve resealed by qualified personnel only. When more than one safety valve is provided, the remaining valve or valves may be set within a range of 3% above the maximum allowable working pressure. However,  the  range  of  the  setting  of  all  the safety valves on the boiler should not exceed 10% of the highest pressure to which any valve is set. Each  safety  valve  should  reseat  tightly  with  a blowdown  of  not  more  than  2  psig  or  4%  of  the valve setting, whichever is greater. In those cases where the boiler is supplied with  feedwater  directly  from  the  pressure  main without  the  use  of  feeding  apparatus  (not including return traps), no safety valve should be set at a pressure greater than 94% of the lowest pressure obtained in the supply main feeding the boiler. 2.   PRESSURE-RELIEF   VALVE—SET- TING REQUIREMENTS. At least one pressure- relief valve should be set to release at not more than  the  maximum  allowable  working  pressure  of the hot-water boiler. When more than one relief valve is provided on either hot-water heating or hot-water supply boilers, the additional valve (or valves) may be set within a range not to exceed 20%  of  the  lowest  pressure  to  which  any  valve is  set.  Each  pressure-relief  valve  should  reseat tightly  with  a  blowdown  of  not  more  than  25% of  the  valve  setting. 3.   SAFETY   VALVE—CAPACITY   TEST. When  the  relieving  capacity  of  any  safety  valve for steam boilers is questioned, it may be tested by  one  of  the  three  following  methods: a.  By  the  accumulation  test,  which  consists of shutting off all other steam-discharge outlets from  the  boiler  and  forcing  the  fires  to  the maximum.  The  safety  valve  capacity  should  be sufficient to prevent a pressure in excess of 6% above the maximum allowable working pressure. Stop and Check Valves While   the   boiler   is   operating,   inspect   the operating condition of each stop and check valve where  possible.  Serious  defects  of  externally controlled  stop  valves  may  be  detected  by operating  the  valve  when  it  is  under  pressure. Similarly, defects in check valves maybe detected by  listening  to  the  operation  of  the  valve  or observing any excessive vibration of the valve as it operates under pressure. Pressure-Reducing Valves While  there  is  pressure  on  the  system,  open and  then  close  the  bypass  valve  as  safety  and operating  conditions  permit.  Also,  observe  the fluctuation  of  the  pressure  gauge  pointer  as  an aid in determining possible defects in the opera- tion  of  the  pressure-reducing  valve  or  the  pressure gauge.  Look  for  any  evidence  that  may  indicate improper  condition  of  the  relief  or  safety  valves provided  for  the  pressure-reducing  valves. Boiler Safety and Water- Pressure  Relief  Valves Test  the  blowoff  setting  of  each  safety  valve for steam boilers and each water-pressure relief valve  for  hot-water  boilers  by  raising  the  boiler pressure slowly to the blowoff point. In turn, test the  releasing  pressure  of  each  valve,  gagging all  other  safety  or  relief  valves  except  the one being tested. Observe the operation of each valve  as  blowoff  pressure  is  reached.  Compare the  blowoff  setting  with  setting  requirements specified  in  paragraph  1  or  2  of  this  section, as  applicable,  and  make  adjustments  where necessary. When the steam discharge capacity of a safety valve is questionable, it should be tested by  one  of  the  methods  given  in  paragraph  3  of this  section.  When  the  pressure-relieving  capacity of  a  pressure-relief  valve  is  questionable,  it  should 12-26

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