TM 1-1500-204-23-2 (1) Petroleum-base fluid MIL-H-6083.  MIL-H-6083 is still authorized for certain uses in Army aircraft.  It is used  as  a  preservative  oil  in  shock  struts,  hydraulic  equipment,  and  spare  parts,  and  as  a  testing  and  flushing  oil  for some components.  It should not be used in operational aircraft hydraulic systems. (2) Petroleum-base fluid MIL-H-5606.   MIL-H-5606 is being phased out for most Army aircraft, and being replaced  with  synthetic-base  fluid  MIL-H-83282.    It  is,  however,  still  used  for  cold  weather  operation.    Refer  to  the following paragraph and paragraph 4-21 for more information on this fluid and its conversion. c. Synthetic-Base  Fluid  MIL-H-83282.    As  stated  above,  MIL-H-5606  is  being  replaced  in  most  operations  by MIL-H-83282.  MIL-H-83282 has a higher flash point and fire point, as well as additives which provide better anti-wear characteristics and provide better resistance to corrosion and oxidation.  Refer to paragraph 4-21 for more information on this fluid and its conversion. d. Precautions.    Use  of  the  correct,  uncontaminated  fluid  in  a  particular  hydraulic  system  is  critical  for  the continued serviceability of that system. (1) Proper fluid.  You must be extremely careful to use only the fluid authorized for a particular component or system.  To determine the correct fluid, consult the applicable technical manual.  In addition, read the instruction plate affixed to the individual unit or reservoir and check the color of the fluid contained in the system. (2) Drained  fluid.    Fluid  drained,  for  any  reason,  from  a  hydraulic  system  or  component  shall  not  be reused. (3) Disposition of containers.   Hydraulic fluid containers, when emptied, shall be destroyed. 2-4 Fluid  Contamination.    Contamination  in  a  hydraulic  system  is  the  presence  of  any  material  other  than  the hydraulic fluid being used.  This includes water, metal, dust, and other solids.  Contamination sources may be internal or external.  Internal contamination can cause abnormal wear of the pump or of other components.  When filters are used too long (especially the paper element type), particles may begin breaking off from the filter element.  Moving seals and backup rings also add contamination to the system.  External contamination is generally caused by poor maintenance practices.    Examples  include  leaving  hydraulic  lines  open  after  removing  a  part,  wiping  fittings  with  dirty  rags;  leaving valves,  tubing,  etc  ,  uncovered  on  workbenches;  changing  fluid  with  dirty  test  equipment,  and  installing  new  or  rebuilt parts that have not been properly cleaned Hydraulic fluid (red color), MIL-H-83282 or MIL-H-5606, shall be used in all hydraulic  systems  The  choice  of  MIL-H-83282  or  MIL-H-5606  depends  on  the  particular  hydraulic  system  and  the ambient temperature Refer to the aircraft manual or to TB 55-1500-334-25. a. Detecting Fluid Contamination.  A kit has been developed, part number 57L414, NSN 6630-00-150-6486, to sample fluid for contamination in order to help control contamination in aircraft.  Contamination checks should become a routine   part   of   your   work.   You   should   check   for   dirt,   metal,   and   visible   solids   every   time   a   unit   is   removed   or disassembled.      Normal   contamination   checks   for   most   aircraft   are   made   by   examining   the   condition   of   the   filter elements.   For example, a clogged filter or an extended filter indicator pin is a symptom of contaminated fluid.  These findings, as well as a pump failure, require flushing of the system. b. System Flushing.  Evidence of contamination makes it necessary that hydraulic system be flushed. CAUTION To avoid contamination, do not use hydraulic fluid that shows evidence of contamination or is in open cans that are stored uncovered/unprotected.  Unused fluid may be kept in filler pumps or sealed jars. (1) Fluid.      Hydraulic   fluid,   MIL-H-5606   or   MIL-H-83282,   shall   be   used   for   flushing   systems   and components.  Discard after use. (2) Accidental servicing.  In the event that a system or component Is Inadvertently serviced with incorrect type fluid, drain fluid, flush system, and replace all packings and gaskets in affected components. c. Contamination Prevention.  Contamination can be prevented by taking the following precautions. (1) Cap or plug all open connections when removing a part. (2) Never use dirty rags to wipe off connections. 2-6