TM 1-1500-204-23-1 (4) Check   valves.      Replace   all   faulty   check valves   as   complete   units.      Check   valves   cannot   be repaired. WARNING Do    not    use    masking    tape    to    seal openings  in  oxygen    regulators.    Its use          on          either     serviceable     or repairable oxygen equipment constitutes a safety hazard (5) Regulators.    Do  not  apply  oil  or  grease  to any part of an oxygen regulator. (6) Flexible hose.  Maintain flexible hose using the following procedures (a) To  remove  contamination  other  than oil and grease from flexible hose, remove hose and clean with    mild    soap,    A-A-50,    and    warm    water    solution, thoroughly rinse with fresh water and thoroughly dry with a stream of clean, dried, water-pumped air or nitrogen (b) Replace hoses damaged or contaminated with oil or grease.  Repair and replacement procedures  for  flexible  hose  are  outlined  in  TM  1-1500- 204-23-2. (c) Examine fittings for tightness. (7) Open lines.  Plug or cap all open lines and equipment  when  opening  system  for  replacement  of  any part    When    system    has    been    accidentally    left    open, system will be purged by one of the following methods • In  aircraft  having  filler  lines  connected  to  one end of cylinder, and distribution lines connected to   opposite   ends   of   cylinder,   purging   will   be accomplished by connecting a service trailer to aircraft   filler   valve   With   all   regulators   open, pass   oxygen   through   system   for   at   least   30 minutes at a pressure of 50 psi at filler valve • In   aircraft   having   filler   lines   and   distribution lines    commonly    connected    at    one    end    of cylinder, purging will be accomplished by filling system  with  oxygen  and  then  draining  system This   cycle   shall   be   performed   at   least   three times. (8) Charging  after  flight.      Charge   oxygen system  on  aircraft  that  have  had  all  the  oxygen  supply drained during flight within two hours after landing. When oxygen   system   is   not   charged   within   two   hours   after landing, system will be purged. NOTE • Do  not  use  lubricant  other  than antiseize   tape,   MIL-T-27730,   on aircraft oxygen systems • Do not use cleaning solutions, or any   other   solutions,   inside   any part    of    oxygen    system    when Installed in aircraft. • Do not use any gases other than oxygen Inside any part of oxygen system when Installed in aircraft. c. Servicing of Oxygen Systems.  Prior to servicing an   aircraft   oxygen   system,   personnel   shall   familiarize themselves with the system, precautions, and instructions for    handling    gaseous    oxygen,    operation    of    servicing equipment,   and   potential   hazards   involved.      Oxygen servicing requires the utmost precautionary measures due to   the   highly   explosive   and   flammable   capabilities   of oxygen All personnel shall heed the following precautionary procedures when servicing: CAUTION Only    qualified    personnel    shall    be authorized   to   operate   equipment   for servicing of an aircraft oxygen system Damage  to  equipment  may  otherwise result. (1) Aircraft  shall  not  be  serviced  with  oxygen when any of the following conditions prevail, • Aircraft electrical switches are on. • Ground      powered      equipment      is   operating within 50 feet of the servicing area. • Aircraft  is  being  serviced  with  fuel,  oil,  or  anti- icing fluids • Any    combustible    materials,    fluids,    etc.,    are evident around oxygen servicing equipment. 9-41