at the gauge glass fittings may indicate a false liquid level. Brine Density Proper brine density should be maintained at 1.5/32. If the brine concentration is too low, there will he a loss in capacity and economy. If the brine concentration is too high, there will an increase in the rate of scaling of the evaporator heating surfaces. FLASH-TYPE  DISTILLING  PLANTS Many   maintenance   procedures   for   flash-type distilling  plants  are  similar  to  the  maintenance procedures  required  for  submerged-tube  distilling plants. Both types of plants are subject to air leakage, saltwater  leakage,  and  malfunctioning  of  pumps  and other auxiliary equipment. HEAT-RECOVERY DISTILLING PLANTS Heat-recovery   distilling   plants   are   single-effect distilling  plants  with  a  submerged-tube  heat  exchanger. This heat exchanger uses heat energy contained in the jacket  cooling  water  circulated  through  diesel  main propulsion  engines  and  ship’s  service  diesel  generators. This unit requires no steam for air ejectors because feed is used as the motive power to operate eductors for air and brine removal To supplement the heat in the jacket cooling water when engines are running at low rates, the plant has electric heating modules and steam heaters. This ensures that the jacket cooling water will be at the required  temperature  when  it  enters  the  submerged-tube heat exchanger. The jacket water passes through all the heat exchangers (whether energized or not) to the inlet of   the   submerged-tube   bundle.   Here   the   heat   is transferred through the tubes to the feed in the boiling compartment.  The  jacket  water  then  exits  the  tube bundle  and  returns  to  the  engine.  The  heat-recovery system  is  fitted  with  a  circulating  pump  and  an expansion tank Most  heat-recovery  distillers  aboard  Navy  ships have  a  secondary  heat  exchanger  between  the  engine jacket cooling water system and the distiller unit. This heat exchanger isolates the engine coolant, with all its chemical  additives,  from  the  distiller.  Systems  not having this secondary heat exchanger get heat directly from the engine coolant to support the distiller. This is called a single-loop system. A single-loop system must be  monitored  continuously  to  ensure  that  no  engine coolant leaks through the distiller submerged-tube heat exchanger.  For  more  information  on  the  monitoring requirements,  refer  to  NSTM  Chapter  233,  “Diesel Engines.”  For  cleaning  heat-recovery  plants,  follow  the applicable instructions as you would for cleaning the submerged-tube or the flash-type distilling plants. For more detailed information concerning the distilling units the Navy uses, refer to the manufacturer’s manual and NSTM, Chapter 531, Volumes 1, 2, and 3, “Desalination Low-Pressure Distilling Plants.” HYDRAULIC  SYSTEMS The  overall  efficiency  of  the  hydraulic  installations used to control or drive auxiliary machines is basically dependent upon the size, oil pressure, speed, and stroke of  the  hydraulic  installation.  The  efficiency  of  the hydraulic speed gears and the components of the system will depend upon the care that is given to them. Except for piping and fittings, major repairs of hydraulic gear are  generally  done  in  a  naval  shipyard  or  by  the manufacturers.  This  section  will  deal  primarily  with troubleshooting   and   preventive   maintenance   of hydraulic systems, including external hydraulics. Hydraulic transmissions are sturdy, service-proven machines,  inspected  and  tested  with  such  care  that casualties seldom occur. When casualties do occur it is usually  the  result  of  faulty  assembly,  installation,  or maintenance.  A  correctly  installed  hydraulic  system, operated regularly and serviced with proper care, will retain  its  design  characteristics  of  power,  speed,  and control. The need for costly repair and replacement will seldom  occur  if  the  equipment  has  been  maintained properly. TROUBLESHOOTING Troubleshooting   an   electrohydraulic   system involves  the  systematic  elimination  of  the  possible causes, one by one, until the actual cause of a casualty is found. In attempting to locate the source of any trouble in  an  electrohydraulic  system,  remember  that  all troubles  fit  into  one  of  three  categories.  It  is  either hydraulic, electrical, or mechanical. Isolating a trouble into one of these categories is one of the main steps in finding  the  source  of  trouble. Hydraulic  Troubles Casualties in a hydraulic system are generally the result  of  low  oil  levels,  external  or  internal  leakage, clogged  lines  or  fittings,  or  improper  adjustment  of valves and other working parts. Do NOT disassemble a unit unless you are certain that the trouble exists within that  unit!  Unnecessary  disassembly  may  create 8-6