TM 1-1500-204-23-5 b.   Inspect  propeller  and  parts  visually  for  damage and,   without   disassembling   units,   ensure   that   all   parts which are accessible fit properly. WARNING Drycleaning     solvent     is     flammable     and solvent   vapors   are   toxic.      Use   P-D-680, Type   II   Solvent   in   a   well-ventilated   area. Keep    away    from    open    flames.        Avoid prolonged solvent contact with skin. c.    Carefully  stone  down  all  galling  or  scoring  on jointed    surfaces    or    attaching    parts,    and    all    minor corrosion,   raised   edges,   nicks,   burrs,   and   cuts.      After stoning   or   dressing   propeller   parts,   remove   any   small metal particles with drycleaning solvent, Federal Specification P-D-680. CAUTION Do not clean propellers with aromatic fuels. 2-13.      Propeller   Governors.      Principles   of   operation, model  designation,  single  capacity  governors,  turbo  prop governors, turbo prop overspeed governors, and integrated  oil  control  units  are  described  in  the  following paragraphs. a.        Principles    of    Operation.        Constant-speed propellers   are   controlled   by   a   speed   governor   which automatically    adjusts    propeller    pitch    to    maintain    a selected engine speed.  If the rpm of the propeller tends to    increase,    the    governor    senses    the    increase    and responds    by    causing    the    propeller    blade    angle    to increase.  Also, when the propeller rpm tends to decrease, the governor causes a decrease in propeller blade angle. An  increased  blade  angle  will  cause  a  decrease  of  rpm, and  a  decreased  blade  angle  will  cause  an  increase  of engine rpm. b.    Model  Designation.    There  are  two  models  of propeller    governors.        One    type,    the    single-capacity governor, operates by applying oil pressure to or releasing oil  pressure  from  a  servo  piston.    The  second  model, called  a  double  action  governor,  applies  oil  pressure  to either side of a double action servo piston. c.  Single Capacity Governors.  The single capacity governor    is    a    single-acting,    self-contained    unit.        It regulates   engine   speed   by   varying   the   pitch   of   the propeller.      The   single   capacity   governor   only   reduces blade pitch by producing an oil pressure increase against a  servo  piston.    The  governor  works  to  counteract,  as necessary, the increase in blade pitch which is accomplished by a combination of counterweights on the propeller   blades   and   feathering   springs   in   the   servo piston. d.    Turbo  Prop  Overspeed  Governors.    The  turbo prop governor and fuel control are connected and operate in coordination with each other.  The power lever directs a signal  from  the  cockpit  to  the  fuel  control  for  a  specific amount  of  power  from  the  engine.    The  fuel  control  and the    propeller    governor    together    establish    the    correct combination  of  rpm,  fuel  flow,  and  propeller  blade  angle to create sufficient propeller thrust to provide the desired power. e.    Turbo  Prop  Overspeed  Governors.    The  speed governor acts as a safeguard against propeller overspeed in the event of constant speed governor failure.  The unit in   the   governor   which   acts   automatically   to   regulate engine speed is the speed-sensitive element.  This unit is affected by centrifugal force and spring pressure.  When engine  speed  is  excessive,  the  centrifugal  force  on  the speed-sensitive  element  overcomes  spring  pressure  and the element moves the distributor valve to route hydraulic fluid  under  pressure  to  the  pitch-change  (torque)  units  at the base of the propeller blades. f.  Integrated Oil Control Assembly.  The integral oil control assembly contains the oil supply for operating the propeller.      This   oil   is   independent   of   the   engine   oil system.    The  oil  control  assembly  also  contains  a  main pump  which  is  driven  by  propeller  rotation.    The  main pump  delivers  oil  continuously  to  the  propeller  governor. For single-capacity governors, oil pressure is increased or   decreased.      For   double-acting   governors,   the   oil   is directed   to   either   the   inboard   or   outboard   side   of   the double-acting piston, to decrease or increase blade angle, respectively. 2-14.        Rigging    Governed    Propellers.        Oil    control plugging, installation, rigging, and operational checks are described in the following paragraphs. a.      Oil   Control   Plugging.      Many   governors   are designed  so  that  they  may  be  adapted  for  either  single action   or   double-action   operation.      As   a   single-action governor, it directs oil pressure to the rear of the cylinder to decrease pitch and allows it to drain from the cylinder when centrifugal force increases pitch.  Propellers having counterweights use single-action governors. The counterweights    and    centrifugal    force    act    together    to increase  pitch.    For  those  propellers  which  do  not  use counterweights to increase pitch, oil from the governor is used to increase pitch by overcoming the centrifugal Change 2    2-16