SERVICE MANUAL Fig. 2 Tractor Protection Valve 1 RING, Snap 11    SCREW 2 SEAL, O-Ring 12    SPRING 3 CAP, End 13    VALVE, Rubber 4 SEAL, O-Ring 14    SEAL, O-Ring 5 VALVE, Exhaust 15    SEAL, O-Ring Assembly 16    SEAL, O-Ring 6 SPRING 17    PISTON 7 SPOOL 18    SEAL, O-Ring 8 SEAL, O-Ring 19    SPRING 9 COVER, End 20    BODY 10    LOCKWASHER 21    SEAL, O-Ring bly  (5)  away  from  body  seat  (20),  seats  assembly  (5) against rubber valve (13) and pushes it away from spool seat   (7).   Service   and   emergency   air   passages   from tractor to trailer ports are open. Exhaust   seats   are   closed,   blocking   air   from   passing through cavities "B" and "C" to atmosphere. During  normal  service  brake  release,  brake  control  air supplied through the downstream of the tractor protection  valve  acts  to  unseat  valve  (13)  from  exhaust valve (5). Air enters cavity "C," goes through "B" and out exhaust port (J). Air  upstream  from  tractor  protection  valve  is  exhausted through foot valve or hand control valve. If  tractor  brake  system  pressure  drops  to  172276  kPa (25-40 psi), spring force (19) moves piston (17) towards exhaust  port  (J).  Simultaneously,  springs  (6)  and  (12) push  assembly  (5)  and  valve  (13)  to  follow.  Tractor-to- trailer  passages  are  closed  and  trailer  emergency  air  is exhausted through "B." Trailer brakes apply automatically. If    the    two-way    air    control    valve    is    pulled    "out"    for emergency   braking   or   uncoupling   trailer,   the   pilot   air exhausts from cavity "A." Tractor protection valve attains closed position and trailer brakes apply. MAINTENANCE Once  each  year  or  every  160,000  km  (100,000  miles) remove,   disassemble   and   clean   all   parts.      All   rubber parts must be replaced. SERVICE CHECKS Leakage Test Use  air  pressure  source  equipped  with  in-line  manual shut-off air gauge and connection. Install  pipe  plugs  in  any  threaded  ports  not  shown  or labeled by Fig. 2. Connect air line to tractor service port (E). Open manual valve slowly to build up 681-861 kPa (100- 125  psi)  and  shut  off  manual  valve.  No  air  leakage  is permissible     through     end     cover     and     body     casting surfaces,   around   screws   and   jointing   flanges.   No   air leakage  permissible  that  is  passing  through  valve  and evident   at   tractor   emergency,   trailer   service   (E)   and emergency (D) or exhaust (J) ports. Disconnect air line from tractor service port and connect to  tractor  emergency  port.  Build  up  681-861  kPa  (100- 125  psi),pressure.  No  air  leakage  permissible  through surrounding   casting   surfaces.   No   leakage   permissible through  valve  and  evident  at  tractor  service  (F),  trailer service (E), and emergency or exhaust ports. Disconnect air line. Connect  air  line  to  control  port.  Build  up  681861  kPa (100-125  psi)  air  pressure.  No  air  leakage  permissible through  casting  surfaces  or  evidence  of  air  leakage  out any of the other five open ports or around end cap snap ring. Disconnect air line. Operation Tests Performance Checks:  An additional manifold fixture with two connections, air gauge and manual shut-off valve will be   required   for   performance   checks.   Preferably,   the manifold should be supplied with air by a separate line to the air source. Install     separate     air     gauges     in     trailer     service     and emergency  ports  (E  and  D).  Connect  manifolded  fixture to control port (H) and tractor emergency port (G). Open manual    valve    to    allow    345379    kPa    (50-55    psi)    air pressure  build  up  to  both  ports.  Shut  off  manual  valve. Pressure  build  up  at  trailer  emergency  port  (D)  should have occurred. Gauge at trailer service port (E) must not show pressure. Permissible leakage at exhaust port is a 25 mm (1") diameter bubble in six (6) seconds. CTS-4079 - CHAPTER XI - Page 4