TM 10-3930-671-24 FIGURE 1.4. D. TRANSFER PUMP The positive-displacement, vane-type fuel transfer pump consists  of  a  stationary  liner  and  spring-loaded  blades which  are  carried  in  slots  in  the  rotor.  Since  the  inside diameter of the liner is eccentric to the rotor axis, rotation causes the blades to move in the rotor slots. This  blade  movement  changes  the  volume  between  the blade segments. Transfer pump output volume and pressure increases as pump speed increases. Since displacement and pressure    of    the    transfer    pump    can    exceed    injection requirements, some of the fuel is recirculated by means of  the  transfer  pump  regulator  to  the   inlet   side   of   the transfer pump. Figure    1.5    illustrates    the    pumping    principle.    Radial movement   causes   a   volume   increase   in   the   quadrant between  blades  1  and  2  (Figure  1.5a).  In  this  position, the quadrant is in registry with a kidney-shaped inlet slot in    the    top    portion    of    the    regulator    assembly.    The increasing  volume  causes  fuel  to  be  pulled  through  the inlet fitting  and  filter  screen  into  the  transfer  pump  liner. Volume  between  the  two  blades  continues  to  increase until blade 2 passes out of registry with the regulator slot. At   this   point,   the   rotor   has   reached   a   position   where outward  movement  of  blades  1  and  2  is  negligible  and volume  is  not  changing  (Figure  1.5b).  The  fuel  between the blades is  being  carried  to  the  bottom  of  the  transfer pump liner. As blade 1 passes the edge of the kidney-shaped groove in the lower portion of the regulator assembly (Figure     1.5c),     the     liner,     whose     inside     diameter     is eccentric to the rotor, compresses blades 1 and 2 in an inward  direction  (Figure  1.5a).  The  volume  between  the blades    is    reduced    and    pressurized    fuel    is    delivered through  the  groove  of  the  regulator  assembly,  through the   transfer   pump,   through   the   rotor,   past   the   rotor retainers  and  into  a  channel  on  the  rotor  leading  to  the hydraulic     head     passages.     Volume     between     blades continues    to    decrease,    pressurizing    the    fuel    in    the quadrant, until blade 2 passes the groove in the regulator assembly. FIGURE 1.5. REGULATOR ASSEMBLY OPERATION Figure 1.6 shows the operation of the pressure regulating piston  while  the  pump  is  running.  Fuel  output from the discharge side of  the  transfer  pump  forces  the piston  in  the  regulator  against  the  regulating  spring.  As flow increases, the regulating spring is compressed until the  edge  of  the  regulating  piston  starts  to  uncover  the pressure   regulating   slot   "S"   (Figure   1.6b).   Since   fuel F-217