TM 55-1510-220-10 e. Fuel    Flow    Indicators.        Two    gages    on    the instrument  panel  (fig.    2-30)  register  the  rate  of  flow  for consumed fuel as measured by sensing units coupled into the fuel supply lines of the respective engines.  The fuel flow indicators are calibrated in increments of hundreds of pounds   per   hour.      Both   circuits   are   protected   by   0.5- ampere  circuit  breakers  placarded  FUEL  FLOW  No.1  or No.2, on the overhead circuit breaker panel (fig. 2-27). Section IV.  FUEL SYSTEMS 2-34.  FUEL SUPPLY SYSTEM. The engine fuel supply system (fig.  2-13) consists of two identical  systems  sharing  a  common  fuel  management panel (fig.  2-14) and fuel crossfeed plumbing (fig.  2-15). Each   fuel   system   consists   of   five   interconnected   wing tanks,  a  nacelle  tank,  and  an  auxiliary  inboard  fuel  tank. A fuel transfer pump is located within each auxiliary tank. Additionally,    the    system    has    an    engine-driven    boost pump,  a  standby  fuel  pump  located  within  each  nacelle tank,   a   fuel   heater   (engine   oil-to-fuel   heat   exchanger unit), a tank vent system, a tank vent heating system and interconnecting wiring and plumbing.  Refer to Section IX for  fuel  grades  and  specifications.    Fuel  tank  capacity  is shown  in  table  2-2.    Gravity  feed  fuel  flow  is  shown  in figure 2-16. a. Engine Driven Boost Pumps. CAUTION Engine   operation   using   only   the engine-driven primary (high pressure) fuel pump without standby     pump     or     engine-driven boost pump fuel pressure is limited to    10    cumulative    hours.        This condition is indicated by illumination   of   either   the   No.1   or No.2 FUEL PRESS warning annunciator lights and the simultaneous   illumination   of   both MASTER WARNING lights.  Refer to Chapter 9.  All time in this category shall  be  entered  on  DA  Form  2408- 13 for the attention of maintenance personnel. A    gear-driven    boost    pump,    mounted    on    each engine  supplies  fuel  under  pressure  to  the  inlet  of  the engine-driven   primary   high-pressure   pump   for   engine starting  and  all  normal  operations.    Either  the  engine- driven    boost    pump    or    standby    pump    is    capable    of supplying sufficient pressure to the engine-driven primary high-pressure   pump   and   thus   maintain   normal   engine operation. b. Standby Fuel Pumps. A submerged, electrically-operated   standby   fuel   pump,   located   within each   nacelle   tank,   serves   as   a   backup   unit      for   the engine-driven   boost   pump.      The   standby   pumps   are switched off during normal system operations.  A standby fuel pump will be operated during crossfeed operation to pump fuel from one system to the opposite engine.  The correct     pump     is     automatically     selected     when     the CROSSFEED   switch   is   activated.      Each   standby   fuel pump  has  an  inertia  switch  included  in  the  power  supply circuit.  When subjected to a 5 to 6 G shock loading, as in a crash situation, the inertia switch will remove electrical power  from  the  standby  fuel  pumps.    The  standby  fuel pumps  are  protected  by  two  10-ampere  circuit  breakers placarded  STANDBY  PUMP  No.1  or  No.2,  located  the overhead  circuit  breaker  panel  (fig.    2-27),  and  four  5- ampere  circuit  breakers  (2  each  in  parallel)  on  the  hot battery bus. c. Fuel   Transfer   Pumps.      The   auxiliary   tank   fuel transfer  system  automatically  transfers  the  fuel  from  the auxiliary   tank   to   the   nacelle   tank   without   pilot   action. Motive  flow  to  a  jet  pump  mounted  in  the  auxiliary  tank sump  is  obtained  from  the  engine  fuel  plumbing  system, downstream   from   the   engine   driven   boost   pump   and routed   through   the   transfer   control   motive   flow   valve. The  motive  flow  valve  is  energized  to  the  open  position by   the   control   system   to   transfer   auxiliary   fuel   to   the nacelle  tank  to  be  consumed  by  the  engine  during  the initial  portion  of  the  flight.    When  an  engine  is  started, pressure   at   the   engine   driven   boost   pump   closes   a pressure  switch,  which  after  a  30  second  time  delay  to avoid depletion of fuel pressure during starting, energizes the motive flow valve.  When auxiliary fuel is depleted, a low level float switch de-energizes the motive flow valve after a 10 second time delay provided to prevent cycling of the motive flow valve due to sloshing fuel.  In the event of  a  failure  of  the  motive  flow  valve  or  the  associated control  circuitry,  the  loss  of  motive  flow  pressure  when there  is  still  fuel  remaining  in  the  auxiliary  fuel  tank  is sensed by a pressure switch and float switch, respectively,    which    illuminates    a    caution    annunciator placarded No.  1 NO FUEL XFR or No.  2 NO FUEL XFR. During  engine  start,  the  pilot  should  note  that  the  NO FUEL XFR annunciators extinguish 30 to 50 seconds after engine  start.    The  NO  FUEL  XFR  annunciators  will  not illuminate if auxiliary tanks are empty.  A manual override is  incorporated  as  a  backup  for  the  automatic  transfer system.  This is initiated by placing the AUX TRANSFER switch, located on the fuel Change 2   2-28