Quantcast Discharge Cycle
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TM 10-3930-671-24 The  plungers  move  outward  a  distance  proportionate  to the amount of fuel required for injection on the following stroke. If only a small quantity of fuel is admitted into the pumping chamber, as at idling, the plungers move out a short distance. Maximum plunger travel and, consequently,  maximum  fuel  delivery  are  limited  by  the leaf  spring  which  contacts  the  edge  of  the  roller  shoes. Only  when  the  engine  is  operating  at  full  load  will  the plungers  move  to  the  most  outward  position.    Note  that while the angled inlet passages in the rotor are in registry with the ports in the circular charging passage, the rotor discharge port is not in registry with a head outlet (Figure 1.7).  Note  also  that  the  rollers  are  off  the  cam  lobes. Compare their relative positions (Figures 1.7 and 1.8). Discharge Cycle As  the  rotor  continues  to  revolve  (Figure  1.8),  the  inlet passages  move  out  of  registry  with  the  charging  ports. The   rotor   discharge   port   opens   to   one   of   the   head outlets.  The  rollers  then  contact  the  cam  lobes  forcing the   shoes   in   against   the   plungers   and   high-pressure pumping begins. Beginning of injection varies according to load (volume of charging fuel), even though rollers may always strike the cam  at  the  same  position.  Further  rotation  of  the  rotor moves  the  rollers  up  the  cam  lobe  ramps  pushing  the plungers  inward.  During  the  discharge  stroke,  the  fuel trapped  between  the  plungers   flows   through   the   axial passage  of  the  rotor  and  discharge  port  to  the  injection line.   Delivery   to   the   injection   line   continues   until   the rollers  pass  the  innermost  point  on  the  cam  lobe  and begin    to    move    outward.    The    pressure    in    the    axial passage  is  then  reduced,  allowing  the  nozzle  to  close. This is the end of delivery. F. DELIVERY VALVE The  delivery  valve  (Figures  1.9a  through  1.9d)  rapidly decreases   injection   line   pressure   after   injection   to   a predetermined value lower than that of the nozzle closing pressure.  This  reduction  in  pressure  permits  the  nozzle valve to return rapidly to its seat, achieving sharp delivery cutoff   and   preventing   improperly   atomized   fuel   from entering the combustion chamber. FIGURE 1.9. The delivery valve operates in a bore in the center of the distributor rotor. Note that the valve requires no seat only a  stop  to  limit   travel.   Sealing   is   accomplished   by   the close clearance between the valve and bore into which it fits. Since the same delivery valve performs the function of retraction for each injection line, the result is a smooth running engine at all loads and speeds. When  injection  starts,  fuel  pressure  moves  the  delivery valve  slightly  out  of  its  bore  and  adds  the  volume  of  its displacement,  section  "A,"  to  the  delivery  valve  spring chamber. Since the discharge port is already opened to a head outlet, the retraction volume and plunger displacement  volume  are  delivered  under  high  pressure to  the  nozzle.  Delivery  ends  when  the  pressure  on  the plunger   side   of   the   delivery   valve   is   quickly   reduced. FIGURE 1.8. F-219

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