TM 1-1500-204-23-1 NOTE Use  an  external  hydraulic  test  unit  or the    aircraft    hydraulic    system    with engine operating (a) Check  operation  of  down-limit  switch by  unwinding  winch  to  Its  limit  to  assure  that  winch  will stop when cable If fully unwound (b) Check operation of up-limit switch by running cable until up-limit switch is actuated b. Electrical Hoist System.  Maintenance and testing procedures for electric hoist systems are explained in the following paragraphs (1) Maintenance of electric hoist system. Maintenance     of     the     electric     hoist     system     consists primarily   of   replacement   of   defective   parts   using   the following procedures. (a) Replace  hoist  cable  when  kinked  or when cable has been broken strands. (b) Replace     monorail     attaching     parts when found to be defective. (c) Lubricate  hoist  as  prescribed  in the applicable aircraft maintenance manual. (2) Testing  of  electric  hoist  system  Perform  a functional   check,   to   test   the   electric   hoist   system   for operation periodically, and when a unit or electrical wiring is replaced in the system. 9-17.        Oxygen    Systems.        Oxygen    system    types, maintenance,  and  servicing  is  explained  in  the  following paragraphs. a Oxygen System Types.  The design of the various oxygen  system  types  used  in  aircraft  depends  largely  on the   type   of   aircraft,   Its   operational   requirements,   and, where   applicable,   the   pressurization   system.      In   some aircraft  a  continuous-flow  oxygen  system  is  installed  for both passengers and crew.  The pressure demand system is widely used as a crew system, especially on the larger transport  aircraft.    Many  aircraft  have  a  combination  of both   systems   which   may   be   augmented   by   portable equipment. (1) Continuous-flow  system.      The  continuous flow oxygen system is shown in figure 9-35.  The oxygen flows from the charged cylinder through the high-pressure line  to  the  pressure-reducing  valve,  which  reduces  the pressure to that required at the mask outlets.  A calibrated orifice  in  the  outlets  will  control  the  amount  of  oxygen delivered to mask. (2) Pressure-demand system. A simple pressure-demand oxygen system is shown in figure 9-36. Note  that  there  Is  a  pressure-demand  regulator  for  each crewmember,  who  can  adjust  the  regulator  according  to his requirements. b. Maintenance  of  Oxygen  Systems.    Maintenance of     oxygen     systems     Is     described     in     the     following paragraphs. (1) Oxygen   leaks.      Use   soap   test   to locate  leaks  unless  individual  leaks  are  large  enough  for personnel to hear or feel.  Apply soap solution, using mild soap,  A-A-50,  to  suspected  part  using  a  soft  brush  and watch carefully for frothing, bubbling, or growing bubbles WARNING Do not allow petroleum base products to  come  in  contact  with  components of the oxygen system, as explosion or fire may result. CAUTION Drain  tubing  of  all  solutions  and  blow out  with  oxygen  prior  to  installation  in aircraft.    Contamination  may  otherwise result. (2)    Tubing   and   fittings.        Maintenance, repair,   replacement,   and   Installation   of   oxygen   system tubing is given in TM 1-1500-204-23-2. (3) Cylinders Replace all damaged cylinders.  No  maintenance  is  authorized  on  installed  low or high pressure cylinders. NOTE All    low    pressure    oxygen    cylinders which carry a maximum charge of 450 psi    will    be    painted    yellow.        High pressure oxygen cylinders which carry a maximum of 2000 psi will be painted green. 9-39