SERVICE MANUAL pushing end cap out. Install snap ring (1) into valve body groove properly. MIDLAND-ROSS MANIFOLDED TRACTOR PROTECTION VALVE DESCRIPTION The  manifolded  tractor  protection  valve  (Fig.  3)  can be   referred   to   as   a   modular   tractor   protection   valve, since  it  is  one  valve  that  incorporates  several  different functions. The   valve   incorporates   a   manifold   built   into   it   to accommodate two (2) brake valve or foot valve ports and a  hand  control  port  through  two  built  in  two  way  check valves for  service  brake  application.  It  also  incorporates a  quick  release  feature,  automatic  shut  off  on  loss  of emergency trailer air and an automatic bleed back of any trapped service air. Fig. 3 Midland Ross Manifold Tractor Protection Valve Location of Ports of Valve Shown in Fig. 3 1 Trailer Emergency 2 Trailer Service 3 Stop Light Switch 4 Brake Valve Secondary 5 Hand Control Valve 6 Brake Valve Primary 7 Tractor Emergency 8 Exhaust The     manifolded     valve     establishes     whether     the service air brake line connecting tractor and trailer brake systems  is  opened  or  closed.  The  emergency  passage through   the   valve   is   always   open.   The   opening   and closing  of  the  service  air  brake  lines  is  established  by shuttling a spring loaded tapered piston working against piston   forces   developed   by   air   pressure   levels   in   the emergency  passage.  Manual  activation  of  the  valve  is performed by the operator through the use of the Trailer Supply  (red)  knob  at  the  instrument  panel.    When  the Trailer  Supply  Control  is  opened  (knob  pushed  in),  air pressure  is  supplied  to  the  emergency  port  to  open  the tractor protection valve. Pulling the Trailer Supply Control knob "out" exhausts the emergency line at the air control valve allowing the tractor protection valve to close. A  quick  release  feature  incorporated  in  the  service passage serves to improve brake release time response. During    service    brake    release,    the    service    line    air pressure in the trailer system is exhausted to atmosphere  at  the  tractor  protection  valve  as  compared to exhausting at the foot valve or hand control valve. The automatic shut-off bleed back feature allows the valve to automatically shut off under a full service brake application. When the Trailer Supply Control is pulled out while   the   service   brakes   are   applied,   the   bleed   back feature allows the trapped air in the trailer service line to bleed to "0" kPa or psi pressure. During  normal  tractor  operation  without  trailer,  the Trailer  Supply  Control  knob  is  "out"  and  the  "service" passage  at  the  tractor  protection  valve  is  closed.  The Trailer  Supply  Control  valve  blocks  the  air  pressure  to the  emergency  passage  to  the  tractor  protection  valve. Air    passages    leading    from    tractor    system    to    trailer couplings are blocked. When  coupling  the  tractor  to  the  trailer,  the  Trailer Supply   Control   (red)   knob   is   pushed   "in".   Air   flows through  the  tractor  protection  valve  emergency  line  to charge trailer brake system reservoirs. Trailer brakes are released simultaneously if trailer brakes are holding prior to coupling. When the air pressure in the emergency line reaches  approximately  276-345  kPa  (40  to  50  psi),  the tractor protection valve service passage will open. During   normal   tractor-trailer   operation,   the   tractor protection   valve   remains   open,   allowing   air   to   flow   in either   direction   between   tractor   and   trailer   air   brake system. Trailer service  brakes  are  applied  and  released by operation of either the foot brake valve or hand control valve, when air flows through the service passage of the tractor  protection  valve.  Trailer  air  reservoirs  and  brake system     are     replenished     by     air     flow through the emergency passage. OPERATION Refer to Fig. 4 for numbers and letters in parenthesis throughout  this  text  which  applies  to  the  Midland-Ross manifolded tractor protection valve. CTS-4079 - CHAPTER XI - Page 6