line just before the auxiliary exhaust steam enters the DFT. In either case, the high-pressure drains end up in the DFT. These  systems  have  basically  the  same  components as the low-pressure steam drain systems. Components specifically  designed  for  high-pressure  steam  and  the addition  of  orifices  are  the  only  major  differences. Whichever system is to be repaired, the system must be tagged. When dealing with repairs on both low-pressure and  high-pressure  steam  systems,  there  should  be  a controlled work procedure package. You should review the QA manual concerning repairs on steam systems. Remember  you  can  request  assistance  from  the personnel who are trained to do the repairs. For more general   information   concerning   steam   plants,   read Boiler Technician 3&2, NAVEDTRA 10535-H. DISTILLING  PLANTS This   section   will   deal   with   inspections, troubleshooting,  and  repairing  of  low-pressure  steam distilling plants. The two most common types used by the  Navy  are  the  submerged-tube  and  the  flash-type distilling  plants.  Additionally,  this  section  will  mention some  facts  about  the  heat  recovery  type  of  distilling plant the Navy also uses. SUBMERGED-TUBE  PLANTS Low-pressure  submerged-tube  distilling  plants differ from ship to ship, but the operating conditions and the maintenance procedures are basically the same. In almost all instances, the personnel who stand watches on  the  distilling  plants  are  also  responsible  for  the maintenance  of  the  plants.  When  operating  problems  do occur, it is the responsibility of the EN2, ENl, or ENC on duty to locate the trouble and to make the necessary adjustments  or  repairs. Distilling plant reliability and consistent operating conditions are essential for satisfactory results. Except under emergency conditions, no plant should be forced beyond  its  rated  capacity.  Requirements  for  higher steam  pressures  result  in  higher  temperatures,  which will cause more rapid scaling of the evaporator tubes. During  operation,  the  various  elements  of  any  plant depend on the heat and fluid balances throughout the plant.  Adjustment  of  any  one  control  can  produce widespread changes to these balances. For example, an increase in the feed to the first effect will raise the liquid level in the first effect. More heat will be required to raise the feed to the boiling point, so that less heat will be available for evaporation in the first-effect shell and a smaller amount of heat will flow to the second-effect tube  nest.  These  changes  produce  a  new  balanced condition, and other adjustments would be required to make  the  new  balance  satisfactory.  Under  such circumstances,   overcontrolling   could   require   many readjustments.  The  operator  will  always  find  it  better  to make small adjustments, one at a time. This will allow enough  time  between  each  adjustment  for  all  the conditions  to  become  steady. Causes of Low Plant Output Failure  to  obtain  full  rated  capacity  is  one  of  the most  frequent  problems  encountered  during  the operation of a distilling plant. The problem may be very difficult  to  remedy  since  it  may  result  from  a combination of things. Adecrease in the distilling output efficiency may result if any of these factors are not met. Full  output  requires  the  following: 1. Proper steam pressure above the orifice a.  Ample  steam  supply b.   Proper operation of reducing valves 2.   Highest  possible  vacuum  in  the  first-effect  tube nest a. b. c. d. e. f. No air leaks Proper water levels in the evaporator shells Continuously vented evaporator tube nests Reasonably clean evaporator tube nests (1)  Continuous  feed  treatment (2)  Mechanically  cleaned  tubes Density of brine overboard not over 1.5/32 (1) Reasonably clean overboard piping (2) Proper valve settings (3)  Proper  operation  of  brine  pump  (clean piping and strainers, proper speed and direction  of  rotation,  properly  vented pump,   properly   packed   and   sealed gland, and no air leaks in the piping) Properly drained tube nests (1)   Proper operation of all drain regulators (2) Proper operation of the tube nest drain pump 3.   Highest  possible  vacuum  in  the  last-effect  shell a. No air leaks 8-2