b. Proper air ejector operation (1) Clean nozzle and strainer (2)   Correct quality and quantity of steam c. Ample flow of circulating water (1) Clean strainer, pipeline, and tubes (2)  Proper  valve  settings (3)   Proper   operation   of   the   circulating pump d. Effective surface in the distilling condenser (1) No undue deposits inside the tubes (2) Proper venting of the condenser (3)  Proper  operation  of  the  condensate pump Steam Pressure A  distilling  plant  cannot  maintain  its  full  output unless  it  is  supplied  with  dry  steam  at  the  designed pressure.  The  orifices  were  constructed  to  pass  the proper amount of steam plus about 5 psig pressure to safely   produce   the   designed   plant   output.   Orifices should  be  inspected  annually.  An  orifice  should  be measured  and  the  reading  compared  with  the  figure stamped on the plate. If necessary, the orifice should be renewed. If the steam pressure above the orifice varies, the exact source of trouble should be located and corrected. First  the  weight-loaded  regulating  valve  and  then  the pressure-reducing  valve  (if  installed)  should  be  checked to  determine  whether  or  not  each  valve  is  operating properly.   If   they   are   functioning   properly   and   the pressure  cannot  be  maintained  above  the  orifice,  you may  assume  that  an  insufficient  amount  of  steam  is being supplied to the plant. The auxiliary exhaust steam supply for the distilling plants,  after  passing  through  the  regulating  valve,  is usually  slightly  superheated  because  of  the  pressure drop through the reducing valve and the orifice plate. A small amount of superheat has little or no effect on the plant  operation  or  the  prevention  of  scale  formation. However, when live steam must be used, the installed desuperheater   spray   connection   should   be   used   to control  the  superheat.  The  water  for  desuperheating must be taken from the boiler feed system, preferably from  the  first-effect  tube  nest  drain  pump.  Water  for desuperheating  must  NEVER  be  taken  directly  from  the fresh  water  distilled  by  the  distilling  plant. Fluctuations  in  the  first-effect  generating  steam pressure  and  temperature  cause  fluctuations  of  pressure and   temperature   throughout   the   entire   plant.   With increased salinity of the distillate, the fluctuations may cause  priming,  as  well  as  erratic  water  levels  in  the shells. These fluctuations may he eliminated by proper operation  of  the  automatic  pressure  regulators  in  the steam  supply  line. First-Effect  Tube  Nest  Vacuum The   range   of   the   pressure   maintained   in   the first-effect tube must be between 16 inches of mercury (in.Hg), with clean tubes, to 1 to 2 in.Hg as scale forms. The output of a submerged-tube type of distilling plant is not greatly reduced until the deposits on the tubes have caused  the  vacuum  to  drop  to  about  atmospheric pressure. When the first-effect tube nest vacuum is lost entirely,  the  reduction  in  output  becomes  very  great. Assuming the reduction in vacuum is due to scale and not to improper operating conditions, the tubes must be cleaned. Keeping the vacuum in the first-effect tube nest as high as possible reduces scale formation to a minimum, enabling  the  plant  to’operate  at  full  capacity. A  vacuum  reduction  that  results  from  any  factor other than deposits on tube surfaces should be corrected to  reduce  deposits  and  greatly  extend  the  intervals between  cleanings.  The  primary  factors  affecting  the first-effect tube nest vacuum are air leakage, low water levels in the evaporator shells, improper venting of the evaporator shells, scale or other deposits on the tubes, and improper draining of the evaporator tube nests. Loss  of  vacuum  resulting  from  deposits  on evaporator   tubes   should   be   gradual.   Under   normal conditions, there will be no major loss of vacuum for any one day’s operation. Any sudden drop in vacuum can be traced to causes other than scale deposits. The  generating  steam  circuit  operates  under vacuum and is subject to air leaks. Leaks from the steam side of the first-effect tube nest to the first-effect shell space  cause  losses  of  capacity  and  economy.  Loss  of vacuum and loss of capacity may be due to air leaks. The air leaks may he from the atmosphere into the generating steam line (downstream from the orifice plate); from the first-effect tube nest front header; or from the first-effect tube  nest  drain  piping.  Air  leaks  in  this  part  of  the distilling plant may be less noticeable than air or water leaks elsewhere, because the effect on the plant is similar to the scaling of the tube surfaces. 8-3