SERVICE MANUAL when  the  reservoir  with  the  highest   pressure   reaches 276 27 kPa (40 5 psi).  If air is depleted quickly, the red  knob  could  pop   immediately.   Leakage   at   exhaust port must not exceed a 25 mm (1") bubble in 5 seconds. 4. With    the    engine    off,    apply    the    foot    valve depleting  the  air  lower.  Air  must  start  to  escape from  the  exhaust  port  when  the  air  pressure  in the  reservoir  with  the  higher  pressure  reaches 207    27.6  kPa  (30    5  psi).    The  yellow  knob may pop out at this time. 5. With   the   engine   off,   deplete   the   air   system further with the foot valve. At 172 27.6 kPa (25  5   psi)   the   yellow   knob   must   pop   out   and maintain  supply  pressure.    Leakage  at  exhaust port  should  not  exceed  25  mm  (1")  bubble  in  5 seconds. 6. Rebuild the supply pressure to at least 276  kPa (40   psi).   Push   in   the   yellow   knob;   the   yellow knob  must  remain  in.  Leakage  at  the  exhaust port should not exceed a 25 mm (1") bubble in 5 seconds. 7. Charge  the  system  to  817  kPa  (120  psi)   and push both knobs in. Pull the red  knob  out.    The yellow knob must remain in. 8. Push  the  red  knob  in  and  pull  the  yellow  knob out.     The     red     knob     must     pop     out     almost instantaneously. 9. Install  a  gauge  to  monitor  tractor  spring  brake delivery  pressure.  Apply  817  kPa  (120  psi)   to both  primary  and  secondary  reservoirs.  Push  in the yellow knob. Delivery  pressure  should  equal the  pressure  in   the   primary   reservoir.   Reduce the  pressure  in  the  primary  reservoir.  Delivery pressure  and  primary  reservoir  pressure  should descend together to 724-621 kPa (105-90 psi) at which point the dual cir, lit supply (double check) valve   shuttle   should   switch   to   the   secondary reservoir  and  delivery  pressure  should  increase to  the  secondary   reservoir   pressure.   After   the primary reservoir pressure is reduced to  zero,  a leakage of a 12.7 mm (1/2") bubble in 5 seconds is   permitted   at   the   primary   reservoir   opening. Close  the  leak  which  had  been  created  at  the primary reservoir. 10. Leaving     the     yellow     knob     in,     recharge     the secondary reservoir to 817 kPa (120 psi). The delivery pressure should also read 817 kPa (120 psi).Recharge  the  primary  reservoir  to  689 kPa    (100    psi).    Slowly    vent     the     secondary reservoir.  As  the  secondary  reservoir  pressure and the delivery line pressure descend  between 793-724    kPa    (115-105    psi),    the    dual    circuit supply    (double    check)    valve    shuttle    should switch   to   the   primary   CTS-4079   C   reservoir, causing the delivery line pressure to adjust to the primary reservoir pressure. 11. Close   all   vents   or   leakage   points   and   charge both  reservoirs  to  817  kPa  (120  psi).    Position the red knob out and the yellow knob in. Develop a leak in the spring brake  delivery  line  and  hold the    yellow    knob    in.        The    primary    reservoir pressure must reduce to zero and the secondary reservoir  pressure  to  138-207  kPa  (20-30  psi). The dual circuit supply valve shuttle should cycle several times during this leakdown period. REMOVE 1. Block and hold vehicle by means other than the parking brakes. 2. Bleed air system completely. 3. Remove   bezel   panel   and   remove   instrument panel access cover, to expose valve body cover plates, Item 1 of Fig. 12. 4. Mark  or  identify  all  air  lines  connected  to  valve. Then disconnect air lines. 5. Remove valve assembly from instrument panel. 6. Remove all fittings from the rear of the valve. Note the direction of all fittings. REINSTALL 1. Assemble  fittings  in  rear  of  valve.  Apply  a  non- hardening  sealing  compound  to  fittings.    Do  not assume.  that the fittings will seal themselves to the body. Maximum torque to apply to the fittings is 14 Nm (10 ft. lbs.). 2. Assemble valve to instrument panel. 3. Connect air lines to their respective fittings (refer to Fig. 7 for porting designation). 4. Charge air  system  and  perform  Service  Checks as outlined. 5. Remove the identification tags. 6. After checking the serviceability of valve, reinstall the bezel and instrument panel access cover. DISASSEMBLY It  should  be  unnecessary  to  remove  the  valve assembly  to  accomplish  the  normal  service  in  replacing the components.  Be  sure  to  block  the  wheels  and  drain all  air  reservoirs.  Remove  the  trim  bezel  to  expose  the valve cover plates.  It is recommended that the valve be serviced by replac- CTS - 4079 - CHAPTER IX - Page 9