of  the  personnel  who  service  and  maintain  the equipment.  During  installation,  maintenance,  and repair  of  hydraulic  equipment,  the  retention  of cleanliness  of  the  system  is  of  paramount importance   for   subsequent   satisfactory   per- formance. The  following  maintenance  and  servicing procedures  should  be  adhered  to  at  all  times  to provide  proper  contamination  control: 1. All tools and the work area (workbenches and  test  equipment)  should  be  kept  in  a  clean, dirt-free   condition. 2.   A   suitable   container   should   always   be provided  to  receive  the  hydraulic  liquid  that  is spilled  during  component  removal  or  disassembly. NOTE:  The  reuse  of  drained  hydraulic liquid is prohibited in most hydraulic systems. In some large-capacity systems the reuse of fluid is permitted.  When  liquid  is  drained  from  these systems for reuse, it must be stored in a clean and suitable  container.  The  liquid  must  be  strained and/or filtered when it is returned to the system reservoir. 3.   Before   hydraulic   lines   or   fittings   are disconnected, the affected area should be cleaned with  an  approved  dry-cleaning  solvent. 4.  All  hydraulic  lines  and  fittings  should  be capped   or   plugged   immediately   after   discon- nection. 5.   Before   any   hydraulic   components   are assembled, their parts should be washed with an approved  dry-cleaning  solvent. 6.  After  the  parts  have  been  cleaned  in dry-cleaning    solvent, they  should  be  dried thoroughly  with  clean,  low-lint  cloths  and lubricated with the recommended preservative or hydraulic  liquid  before  assembly. NOTE:  Only  clean,  low  lint  type  I  or  II cloths as appropriate should be used to wipe or dry  component  parts. 7. All packings and gaskets should be replaced during  the  assembly  procedures. 8. All parts should be connected with care to avoid  stripping  metal  slivers  from  threaded  areas. All  fittings  and  lines  should  be  installed  and torqued   according   to   applicable   technical instructions. 9.  All  hydraulic  servicing  equipment  should be  kept  clean  and  in  good  operating  condition. Some  hydraulic  fluid  specifications,  such  as MIL-H-6083,  MIL-H-46170,  and  MIL-H-83282, contain particle contamination limits that are so low that the products are packaged under clean room  conditions.  Very  slight  amounts  of  dirt, rust,   and   metal   particles   will   cause   them   to fail   the   specification   limit   for   contamination. Since  these  fluids  are  usually  all  packaged  in hermetically  sealed  containers,  the  act  of  opening a container may allow more contaminants into the fluid  than  the  specification  allows.  Therefore, extreme care should be taken in the handling of these  fluids.  In  opening  the  container  for  use, observation, or tests, it is extremely important that the  can  be  opened  and  handled  in  a  clean environment.  The  area  of  the  container  to  be opened  should  be  flushed  with  filtered  solvent (petroleum  ether  or  isopropyl  alcohol),  and  the device used for opening the container should be thoroughly rinsed with filtered solvent. After the container  is  opened,  a  small  amount  of  the material  should  be  poured  from  the  container  and disposed  of  prior  to  pouring  the  sample  for analysis.  Once  a  container  is  opened,  if  the contents are not totally used, the unused portion should   be   discarded.   Since   the   level   of   con- tamination  of  a  system  containing  these  fluids must  be  kept  low,  maintenance  on  the  system’s components  must  be  performed  in  a  clean environment  commonly  known  as  a  controlled environment  work  center.  Specific  information about  the  controlled  environment  work  center  can be  found  in  the  Aviation  Hydraulics  Manual, NAVAIR  01-1A-17. HYDRAULIC  FLUID  SAMPLING The condition of a hydraulic system, as well as  its  probable  future  performance,  can  best  be determined by analyzing the operating fluid. Of particular interest are any changes in the physical and  chemical  properties  of  the  fluid  and  excessive particulate   or   water   contamination,   either   of which  indicates  impending  trouble. Excessive  particulate  contamination  of  the fluid  indicates  that  the  filters  are  not  keeping  the system  clean.  This  can  result  from  improper  filter maintenance,   inadequate   filters,   or   excessive ongoing  corrosion  and  wear. Operating  equipment  should  be  sampled according to instructions given in the operating 3-10