TM 10-3930-671-24 The  DB2  pump  contains  its  own  mechanical  governor capable of close speed regulation.  The centrifugal force of  the  weights  in  their  retainer  is  transmitted  through  a sleeve   to   the   governor   arm   and   through   a   positive linkage  to  the  metering  valve.    The  metering  valve  can be  closed  to  shut  off  fuel  through  a  solid  linkage  by  an independently  operated  shutoff  lever,  or  by  an  electrical solenoid. The automatic advance is a hydraulic mechanism which advances or retards the pumping cycle. B. MOUNTING FLANGES FIGURE 1.1 Shown    above    are    the    typical    DB2    mounting    flange configurations.      These   are   the   three   most   common types.    Note  that  the  automotive  flange  has  scalloped slots  to  enable  it  to  be  mounted  on  a  standard  pump holding fixture. C. FUEL FLOW The operating principles of the pump can be understood more    readily    by    following    the    fuel    circuit    during    a complete pump cycle cutaway, (Figure 1.2) and fuel flow schematic  (Figure  1.3).    Also,  see  exploded  view  of  the rotor assembly (Figure 1.4). Fuel is drawn from the supply tank through filters into the pump inlet through the inlet filter screen (1) by the vane- type   fuel   transfer   pump   (2).      Some   fuel   is   bypassed through   the   pressure   regulator    assembly    (3)    to    the suction side. Fuel   under   transfer   pump   pressure   flows   through   the center of the transfer pump rotor, past the rotor retainers (4)  into  a  circular  groove  on   the   rotor.      It   then   flows through  a  connecting  passage  (5)  in   the   head   to   the automatic  advance  (6),  up  through  a  radial  passage  (7) and   then   through   a   connecting   passage   (8)   to    the metering   valve.      The   radial   position   of   the   metering valve,  controlled  by  the  governor,  regulates  flow  of  the fuel     into     the     radial charging passage (9) which incorporates the head charging ports. As  the  rotor  revolves,  the  two  rotor  inlet  passages  (10) register  with  the  charging  ports  in  the  hydraulic  head, allowing  fuel  to  flow  into  the  pumping  chamber.    With further  rotation,  the  inlet  passages  move  out  of  registry and the discharge port of the  rotor  registers  with  one  of the head outlets.  While the discharge port is opened, the rollers  (11)  contact  the  cam  lobes  forcing  the  plungers together.    Fuel  trapped   between   the   plungers   is   then pressurized and delivered by the nozzle to the combustion chamber. Self-lubrication of the pump is an inherent feature of the Roosa Master design.  As fuel at transfer pump pressure reaches   the   charging   ports,   slots   on   the   rotor   shank allow  fuel  and  any  entrapped  air  to  flow  into  the  pump housing cavity. In  addition,  an  air  vent  passage   (12)   in   the   hydraulic head  connects  the  outlet  side  of  the  transfer  pump  with the pump housing.  This allows air  and  some  fuel  to  be bled  back  to  the  fuel  tank  via  the  return  line.    The  fuel thus  bypassed  fills  the  housing,  lubricates  the  internal components, cools and carries off any small air bubbles. The  pump  operates  with  the  housing  completely  full  of fuel;  there  are  no  dead  air  spaces  anywhere  within  the pump. F-215