TM 1-1510-225-10 2-68 panel.    Place  the    STANDBY  PUMP  switches  in  the OFF  position when crossfeeding.  A lever lock switch, placarded   CROSSFEED  FLOW,  is  moved  from  the center    OFF    position    to    the    left    or    to    the    right, depending on direction of fuel flow desired, to open the crossfeed valve and energize the standby pump on the side     from     which     crossfeed     is     desired.          During crossfeed   operation   with   firewall   fuel   valve   closed, auxiliary    tank    fuel    will    not    crossfeed.        When    the crossfeed mode is energized, a green FUEL  CROSSFEED   annunciator    on    the    caution/advisory panel  will  illuminate.    Crossfeed  system  operation  is described   in   Chapter   9.      The   crossfeed   valve   is protected   by   a   5 -ampere  circuit  breaker,  placarded CROSSFEED,    located    on    the    left    sidewall    circuit breaker panel. CAUTION Do not use the fuel firewall shutoff valve to shut     down     an     engine,     except     in     an emergency. The engine-driven high- pressure     fuel     pump     obtains     essential lubrication   from   fuel   flow.         When   an engine   is   operating,   this   pump   may   be severely damaged (during cavitation) if the firewall valve is closed before the CONDITION  lever  is  moved  to  the  FUEL CUTOFF position. g.  Firewall  Shutoff  Valves.     The  fuel  system incorporates  a  fuel  line  shutoff  valve  mounted  aft  of each engine firewall. Two guarded switches, placarded FIREWALL   SHUTOFF   VALVE   OPEN   /   CLOSED LEFT   /   RIGHT,   located   on   the   left   sidewall   circuit breaker  panel  control  the  firewall  shutoff  valves.  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   5-ampere    circuit    breakers,    placarded FIREWALL VALVE LEFT / RIGHT, on the left sidewall circuit breaker panel. h.  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.  Refer to Table 2-4. (2)   An    additional    drain    for    the    ferry    fuel system  line  extends  through    the  bottom  of  the  wing center  section  adjacent  to  the  fuselage.   Any  time  the ferry   fuel   system   is   in   use,   the   preflight   inspection includes draining a small amount of fuel from this drain to  check  for  fuel  contamination.    Whenever  the  ferry fuel  system  is  removed  from  the  aircraft  and  the  fuel line  is  capped  off  in  the  fuselage,  drain  the  remaining fuel in the line. (3)   Each     ferry     fuel     tank     has     a     10-foot 1/4-inch flex hose with a quick drain installed in the aft end.  When the ferry fuel system is in use, the  preflight inspection  also  includes  draining  a  small  amount  of fuel  from  these  drains  to  drain  off  any  moisture  that may have been inadvertently introduced into the tanks.   Place  the  aft  end  of  the  hoses  out  through  the  cabin entrance  door,  hold  a  fuel-proof  container  under  the ends, and drain about a pint of fuel out of each line. i.    Fuel    Purge    System.        Each     engine     is provided  with  a  fuel  purge  system.    The  system  is designed  to  ensure  that  any  residual  fuel  in  the  fuel manifolds    is    consumed    during    engine    shutdown.   During  engine  operation,  compressor  discharge  air  is routed through a filter and check valve, pressurizing a small air tank mounted on the engine truss.  On engine shutdown the pressure differential between the air tank and  fuel  manifolds  causes  air  to  be  discharged  from the air tank, through a check valve, and into manifolds, out   through   the   nozzles   and   into   the   combustion chamber.        The    fuel    forced    into    the    combustion chamber  is  consumed,  causing  a  momentary  rise  in engine ITT. Table 2-4.  Fuel Sump Drain Locations NUMBER DRAINS 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 flap 1 Ferry Fuel Outboard of fuselage on underside of wing center section