TM 55-1510-219-10 opened,     allows     the     distribution     of     the     pressurized extinguishing agent through a plumbing network of spray nozzles   strategically   located   in   the   fire   zones   of   the engines. b. Fire   Pull   Handles.      The      fire   control   handles, which   are   used   to   arm   the   extinguisher   system   are centrally  located  on  the  pilot's  instrument  panel  (fig.    2- 28),  immediately  below  the  glareshield.    These  controls receive power from the hot battery bus.  The fire detection system   will   indicate   an   engine   fire   by   illuminating   the master   fault   warning   light   on   the   pilot's   and   copilot's glareshield and the respective #1 or #2 FIRE PULL lights in  the  fire  control  T-handles.    Pulling  the  fire  control  T- handle  will  electrically  arm  the  extinguisher  system  and close   the   fuel   firewall   shutoff   valve   for   that   particular engine.    This  will  cause  the  red  light  in  the  PUSH  TO EXTINGUISH  switch  and  the  respective  red  #1  and  #2 FUEL  PRESS  light  in  the  warning  annunciator  panel  to illuminate.          Pressing     the     lens     of     the     PUSH     TO EXTINGUISH  switch  (after  lifting  one  side  of  its  spring- loaded clear plastic guard) will fire the squib, expelling all the  agent  in  the  cylinder  at  one  time.    The  respective yellow   caution   light,   #1   or   #2   EXTGH   DISCH   on   the caution/advisory   annunciator   panel   will   illuminate   and remain illuminated until the squib is replaced. c. Fire  Extinguisher  System  Test  Switch.    A  rotary test   switch,   placarded   FIRE   PROTECTION   TEST,   is located   on   the   copilot's   subpanel.      The   test   functions, placarded EXTGH #1 #2, are arranged on the left side of the switch and provide a test of the pyrotechnic cartridge circuitry.    During  Before  Exterior  Check,  the  pilot  should rotate the test switch through the two positions and verify the   illumination   of   the   green   SQUIB   OK   light   on   the PUSH   TO   EXTINGUISH   switch   and   the   corresponding yellow #1 or #2 EXTGH DISCH light on the caution/advisory annunciator panel. d. Fire Extinguishing System Supply Cylinder Gages.    A  gage,  calibrated  in  PSI,  is  mounted  on  each supply  cylinder  for  determining  the  level  of  charge  and should be checked during preflight (table 2-1). 2-27.  OIL SUPPLY SYSTEM. a. The  engine  oil  tank  is  integral  with  the  air-inlet casting located forward of the accessory gearbox.  Oil for propeller  operation,  lubrication  of  the  reduction  gearbox and  engine  bearings  is  supplied  by  an  external  line  from the high pressure pump.  Two scavenge lines return oil to the  tank  from  the  propeller  reduction  gearbox.    A  non- congealing    external    oil    cooler    keeps    the    engine    oil temperature  within  the  operating  limits.    The  capacity  of each  engine  oil  tank  is  2.    3  U.    S.    gallons.    The  total system  capacity  for  each  engine,  which  includes  the  oil tank, oil cooler, lines, etc.  , is 3.  5 U.  S.  gallons.  The oil level is indicated by a dipstick attached to the oil filler cap.    Oil  grade,  specification  and  servicing  points,  are described in Section XII, Servicing. b. The  oil  system  of  each  engine  is  coupled  to  a heat   exchanger   unit   (radiator)   of   fin-and-tube   design. These exchanger units are the only airframe mounted part of  the  oil  system  and  are  attached  to  the  nacelles  below the engine air intake.  Each heat exchanger incorporates a  thermal  bypass  which  assists  in  maintaining  oil  at  the proper temperature range for engine operation. 2-28.  TORQUE LIMITER A   torque   limiter   is   installed   in   the   torquemeter pressure    transmitter    boss    on    the    front    case    of    the propeller  reduction  gearbox.    The  limiter  incorporates  a sealed   bellows,   connected   directly   to   torquemeter   oil pressure,   which   works   against   an   externally   adjustable torque-limit spring.  Torquemeter oil pressure is sensed at the  inside  of  the  bellows  assembly,  and  during  normal operating  conditions  the  torquemeter  oil  pressure  is  not high  enough  to  compress  the  torque-limit  spring.    When high  torque  pressure  is  sensed,  the  bellows  will  stretch and  compress  the  spring  assembly.    This  will  permit  a limited amount of governing air pressure to be bled from the fuel control unit and will continue to do so until engine speed  is  reduced,  resulting  in  a  proportional  reduction  in engine torque pressure. 2-26