Figure 2-17.  Auxiliary Fuel Tank Mechanical Fuel Gage The   fuel   system   incorporates   a   fuel   line   shutoff valve   mounted   on   each   engine   firewall.      The   firewall shutoff valves close automatically when the fire extinguisher T-handles on the instrument panel are pulled out.    The  firewall  shutoff  valves  receive  electrical  power from  the  main  buses  and  also  from  the  hot  battery  bus which is connected directly to the battery.  The valves are protected    by    circuit    breakers    placarded    FIREWALL VALVE   No.1   or   No.2   on   the   overhead   circuit   breaker panel   (fig.      2-27),   and   FIREWALL   SHUTOFF   No.1   or No.2 on the hot battery bus circuit breaker board. g. Fuel Tank Sump Drains.  A sump drain wrench is provided  in  the  aircraft  loose  tools  to  simplify  draining  a small amount of fuel from the sump drain. (1) There  are  five  sump  drains  and  one  filter drain in each wing (table 2-3). (2) An   additional   drain   for   the   extended   range fuel  system  line  extends  through  the  bottom  of  the  wing center   section   adjacent   to   the   fuselage.      Anytime   the extended  range  system  is  in  use,  a  part  of  the  preflight inspection  would  consist  of  draining  a  small  amount  of fuel   from   this   drain   to   check   for   fuel   contamination. Whenever  the  extended  range  system  is  removed  from the aircraft and the fuel line is capped off in the fuselage, the remaining fuel in the line shall be drained. h. Fuel Drain Collector System.  Each engine is provided  with  a  fuel  drain  collector  system  to  return  fuel dumped  from  the  engine  during  clearing  and  shutdown operations   back   into   its   respective   nacelle   tank.      The system   draws   power   from   the   No.4   feeder   bus.      Fuel transfer  is  completely  automatic.    Fuel  from  the  engine flow divider drains into a collector tank mounted below the aft   engine   accessory   section.      An   internal   float   switch actuates  an  electric  scavenger  pump  which  delivers  the fuel to the fuel purge line just aft of the fuel purge shutoff valve.  A check valve in the line prevents the backflow of fuel  during  engine  purging.    The  circuit  breaker  for  both pumps   is   located   in   the   fuel   section   of   the   overhead circuit breaker panel; placarded SCAVENGER PUMP.  A vent  line,  plumbed  from  the  top  of  the  collector  tank,  is routed     through     an     inline     flame     arrestor     and     then downward  to  a  drain  manifold  on  the  underside  of  the nacelle. i. Fuel  Vent  System.    Each  fuel  system  is  vented through  two  ram  vents  located  on  the  underside  of  the wing adjacent to the nacelle.  To prevent icing of the vent system,   one   vent   is   recessed   into   the   wing   and   the backup vent Table 2-3.  Fuel Sump Drain Locations NUMBER DRAIN LOCATION 1 Leading Edge Tank Outboard of nacelle, underside of wing 1 Integral Tank Underside of wing, forward of aileron 1 Firewall fuel filter Underside of cowling forward of firewall 1 Sump Strainer Bottom center of nacelle forward of wheel well 1 Gravity feed line Aft of wheel well 1 Auxiliary Tank At wing root, just forward of the flap 2-34