SERVICE MANUAL When  the  brake  valve  is  released,  air  pressure  acting above   piston   is   removed.      Air   pressure   in   cavity   "B" continues   to   move   the   piston   upward   and   opens   the exhaust   valve   seat.      Air   pressure   from   service   brake chambers     returns     through     the     delivery     ports     (not illustrated in Fig. 2) into cavity "B" and exhausts through modulation tube passage and out exhaust port. MAINTENANCE Once  each  year  or  every  160,000  km  (100,000  miles) remove the relay quick release valve, disassemble it and clean  all  parts.    It  is  recommended  that  all  rubber  parts be replaced. SERVICE CHECKS Leakage Tests Use an air pressure source with an in-line shut-off valve, gauge and connection.  A second air source connection will also be required with a shut-off. Install a pipe plug in one delivery port and one reservoir port.      Connect   air   source   with   gauge   to   control   port. Open manual valve slowly to build up 689 - 861 kPa (100 - 125 psi) to control port and shut manual valve.  No air leakage  is  permissible  through  cover  and  body  casting surfaces,   around   capscrews   or   joined   flanges.   No   air leakage is permissible that is passing through valve and evident  at  reservoir  port  or  out  exhaust  port  or  around the  snap  ring.    Slowly  disconnect  air  line  to  release  air pressure from control port. Connect  air  source  to  reservoir  port  and  open  manual valve  slowly  to  build  up  689  -  861  kPa  (100  -  125  psi) pressure.      Shut   off   manual   valve.   No   air   leakage   is permissible  through  casting  surfaces  or  at  exhaust  port or around snap ring area. Operation Test Open manual valve to build up 689 - 681 kPa (100 - 125 psi)  pressure  at  reservoir  port.     Connect   air   line   with gauge to control port.  Open shut-off valve to allow 69 - 103  kPa  (10  -  15  psi)  to  control  port  and  close  valve. Delivery port pressure indicated will be within +21 kPa (3 psi) of that shown at control port.  Permissible leakage at exhaust port is a 25 mm (3") soap bubble in 3 seconds. Open shut-off valve to allow 655 - 689 kPa (95 - 100 psi) to  control  port  and  close  valve.    Repeat  observation  of delivery     port     pressure     and     exhaust     port     leakage. Delivery  port  pressure  should  be  696  -  765  kPa  (101  - 111  psi).    Permissible  leakage  at  exhaust  port  is  a  25 mm (3") soap bubble in 3 seconds. If relay quick release will not perform as described, it should either be replaced or repaired. REMOVE 1. Disconnect air lines from relay valve. 2. Remove mounting bolts and remove valve. INSTALL 1. Mount    relay    valve    with    mounting    bolts    and lockwashers with exhaust port pointing down. 2. Connect air lines. 3. Make sure exhaust port is not restricted. 4. Make   sure   new   or   rebuilt   valve   is   tested   as outlined in SERVICE CHECKS prior to installation. DISASSEMBLY After  the  relay  valve  is  removed  from  vehicle,  inspect  it for damage.  If valve body is fractured replace complete valve.        Mark    exterior    of    valve    cover    and    body    for alignment. 1. Remove four cover capscrews. 2. Remove valve cover, piston assembly and piston spring, if equipped, from valve body. 3. Remove  retaining  ring  from  valve  body,  using  a snap ring pliers.  Then remove washer, exhaust valve   body   spring   and   modulation   tube   from valve body. 4. Remove O-ring seal from valve body. 5. Remove capscrew exhaust valve seal and piston O-ring seal from piston. 6. Remove screw, washer and exhaust port diaphragm from exhaust valve body. 7. Remove O-ring seal, inlet seal retainer and inlet valve seal from modulation tube. 8. Remove O-ring seal from valve cover. CLEANING AND INSPECTION Wash all parts in clean mineral spirits or equivalent and dry.  Castings must be free of nicks or burrs.  All O-ring surfaces  A  rust  be  smooth,  round  and  free  of  deep  - scratches,    dents    or    gouges.        There    should    be    no evidence of metal-to-metal galling of aluminum surfaces. Valve body flanges, threads and snap ring groove should not   be   distorted.      Valve   body   seat   must   be   flat   and smooth, with no cracks or nicks. Examine  modulation  tube.    Flange  for  valve  seal  must not be dented or bent.  Seal at end of tube must be flat and smooth with no dents or distortion. CTS -4079-CHAPTER VI - Page 3