TM 1-1500-204-23-9 (d) Oil  and  water  accumulation.    Open the  siphon  valve  and  drain  accumulated  water  and  oil from receiver. (7) Maintenance.        Consult    the    applicable maintenance   manual   for   scheduled   and   preventive maintenance requirements. h. Aircraft    Preheater.    The    aircraft    preheater, shown   in   figure   9-15,   will   deliver   40,000   to   400,000 BTUs/hour    within    the    specified    operating    condition limits.    The  preheater  will  deliver  uncontaminated  air with  a  regulated  discharge  air  temperature  of  150  to 280°F (66 to 138C)at an adjustable air delivery rate of 435  to  815  cfm.    Flexible  ducts  are  used  to  direct  the heated air where it is needed. (1) Purpose.          The    aircraft    preheater    is specifically     designed     to     preheat     aircraft     engines, cockpits and cabins when the aircraft is in cold weather areas.      It   is   often   used   to   provide   heat   to   aircraft repairers  as  they  perform  outdoor  maintenance  in  the winter. (2) Principles   of   operation.      The   aircraft preheater   has   a   prime   mover   assembly   and   a   heat generator assembly. (a) Prime mover assembly.    The  prime mover is either a gas engine or an electric motor which drives  afan,  a  fuel  pump,  and  a  magneto.    The  fan moves the air to be heated through the heat exchanger section  of  the  heat  generator  and  also  supplies  the  air for   combustion.      The   fuel   pump   supplies   fuel   for combustion  in  the  heat  generator  and  to  run  the  gas engine.    The  magneto  ignites  the  combustion  fuel  and air   mixture   in   the   combustion   portion   of   the   heat generator. (b) Heat generator assembly.    Through the  medium  of  a  heat  exchanger,  the  heat  generator heats  the  inlet  air  with  hot  gases  generated  by  fuel burned in the combustor.  The air and exhaust flow are so   arranged   that   there   can   be   no   intermingling   of exhaust gases with the heated air. (3) Safety   practices   and   procedures.      The following  special  precautions  should  be  observed  when using the aircraft preheater: ·  Do  not  use  inside  a  structure  due  to  possible carbon monoxide poisoning.  Park the preheater outside and run ducting to the inside. ·  Periodically look for leaks in the fuel system. ·  Locate  the  unit  so  that  the  exhaust  does  not blow into the inlet door. ·  Let the unit cool down before refueling. ·  Be sure the exhaust stack extension is in place. ·  Ensure   all   outlet   and   inlet   access   doors   are open. (4) Operating procedures. Consult     the applicable maintenance manual for detailed instructions. The    following    general    procedures    pertain    to    the operation of the aircraft preheater: (a) Position  the  preheater  so  that  the wind blows the exhaust away from the air inlet opening. (b) Open  the  air  inlet  canopy  door,  air outlet doors, access doors, and the exhaust stack door. (c) Connect     the     flexible     duct     and position it as needed. (d) If    using    the    gas    engine    prime mover,  start  the  engine.    If  using  the  electric  motor prime mover, plug it in to a power source, normally 115 vac, and turn switch on. (e) Regulate   the   heat   by   using   the temperature selector valve. (f) To    stop    the    preheater,    pull    the burner  fuel  knob  to  stop  the  combustor  fire.    Allow  the prime  mover  to  run  for  about  2  minutes  for  cooling purposes. (g) Stop  the  prime  mover  by  pressing the  stop  switch  button  on  the  gas  engine  or  by  turning the switch on the electric motor to off. (5) Inspection.    The  operator  should  perform the    following    general    inspections    before    using    the aircraft preheater.  Detailed inspection requirements are found in the applicable maintenance manual. (a) Gas tank.  Check the level and refill as necessary. 9-42