SERVICE MANUAL INVERSION VALVE DESCRIPTION The  inversion  valve  is  a  Bendix,  TR-3  valve,  which  is  a pilot operated, non-graduated two way valve.  The valve will   be   found   in   the   cruise   control   system   where   it functions as an on-off air control valve. When  operating  the   vehicle   with   the   cruise   control   in cruise mode, air  will  pass  through  the  valve.    When  the service brakes are applied through the foot (brake) valve or the hand control valve the inversion valve will exhaust air in the cruise system, thus releasing the cruise control system. Fig. 8 Emergency Relay Valve The  TR-3  type  valve  has  a  separate  control  port  and supply   port;   and   depending   upon   the   piping   of   the vehicle, the control port can either be piped to a separate air  supply  or  can  be  piped  so  that  the  control  and  air supply air pressure are from a common air supply.  In the application  of  cruise  control  system  the  supply  port  will be   connected   to   the   solenoid   control   assembly,   the control  port  will  be  connected  to  the  tractor  protection valve  and  the  delivery  port  will  be  connected  to  the  air cylinder  assembly.  For  complete  operational  description of the cruise control system refer to CRUISE CONTROL in ELECTRICAL GROUP. OPERATION Refer to Fig. 9 for numbers and letters in parenthesis. With  no  air  pressure  at  the  control  port  (D)  the  piston spring (11) forces the piston (9) against the inlet valve (7) closing  the  exhaust  passage  in  the  hollow  piston  stem. The inlet valve (7) is open allowing air passage from the solenoid  valve  through  the  supply  port  (C)  and  out  the delivery port (B). When  the  service  brakes  are  applied  through  the  brake valve or hand control valve the air CTS-4079 - CHAPTE pressure will enter the control port (D) pushing piston (9) away  from  its  seat  and  at  the  same  time  forcing   the piston away from the inlet valve (7) which is held closed by  the  valve  return  spring  (4).    At  this  time  the  delivery line  to  the  air  cylinder  is  vented  to  atmosphere  through the  hollow  exhaust  stem  in  the  piston  (9)  and  out  the exhaust  port  (A),  releasing  the  cruise  control.    The  inlet valve  is  also  closed  off  at  this  time  sealing  the  supply from the solenoid valve assembly. Fig. 9 Crow Section of Emergency Relay Valve A. Exhaust Port B. Delivery Port C. Supply Port D.   Control Port 1. Diaphragm 2. Exhaust Nut 3. O-Ring 4. Valve Spring 5. Cap 6. Valve Stop 7. Valve 8. Shim 9. Piston 10. Diaphragm Retainer 11. Piston Spring MAINTENANCE Once  each  year  or  every  160,000  km  (100,000  miles) perform   the   LEAKAGE   TEST   If   the   valve   failed   the leakage test it must be replaced. CTS-4079-CHAPTER III PRINTED IN UNITED STATES OF AMERICA PAGE -8