SERVICE MANUAL BENDIX D-2 TYPE DESCRIPTION The   air   compressor   governor   along   with   the compressor    unloader    mechanism    automatically    limits system  pressure  to  a  predetermined  range  by  opening unloading     valves     and     stopping     compression     when system pressure has been built up to maximum pressure limit    and    by    closing    unloading    valves    and    starting compression   when   system   pressure   has   dropped   to minimum pressure limit. The  D-2  governor  has  a  piston  upon  which  air pressure  acts  to  overcome  the  pressure  setting  spring and control the inlet and exhaust valve to either admit or exhaust    air    to    or    from    the    compressor    unloading mechanism. Type   D-2   governors   can   be   attached   to   the compressor or mounted remotely.  They are adaptable to either  mounting.    Connections  in  this  system  are  to  the reservoir  and  compressor  unloading  ports.    They  also have an exhaust port. Fig.  1  Type D-2 Governor 1 Unloader Ports 3 Reservoir Ports 2 Mounting Holes 4 Exhaust Port OPERATION (Fig.  2) Reservoir   air   pressure   enters   the   governor   at one  of  its  reservoir  ports  and  acts  on  the  area  of  the piston  and  beneath  the  inlet  and  exhaust  valve.    As  the air   pressure   builds   up,   the   piston   moves   against   the resistance of the pressure setting spring.  The piston and inlet and exhaust valve move up when the reservoir air pressure reaches the cut-out setting of the governor. Fig.  2  Sectional View of Type D-2 Governor 1 Cover 10 Inlet and Exhaust 2 Adjusting Screw Valve 3 Lock Nut 11 Grommets 4 Body 12 Lower Spring 5 Exhaust Stem Seats Spring 13 Spring Guide 6 Exhaust Stem 14 Pressure Setting 7 Filters Spring 8 Piston 15 Upper Spring Seat 9 Inlet-Exhaust 16 Retaining Ring Valve Spring The exhaust stem seats on the inlet and exhaust valve  and  then  the  inlet  passage  opens.    Reservoir  air pressure then flows by the open inlet valve, through  the passage  in  the  piston  and  out  the  unloader  port  to  the compressor   unloading   mechanism.      The   air,   besides flowing  to  the  compressor  unloading  mechanism,  also flows around the piston and acts on the additional area of the piston, assuring positive action and fully opening the inlet valve. As the system reservoir air pressure drops to the cut-in setting of the governor, the force exerted by the air pressure   on   the   piston   will   be   reduced   so   that   the pressure  setting  spring  will  move  the  piston  down.    The inlet valve will close and the exhaust will open.  With the exhaust open the air in the unloader line will escape back through the piston, through the exhaust stem and out the exhaust port. SERVICE CHECKS Operating Tests Start the vehicle engine and build up air pressure in    the    air    brake    system    and    check    the    pressure registered   by   a   dash   or   test   gauge   at   the   time   the governor cuts out, stopping the compression of air by the compressor.        The    cut-out    pressure    should    be    in accordance with the piece num- PRINTED IN UNITED STATES OF AMERICA CTS-4079 - CHAPTER I Page 2