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.
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
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.
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
Disconnect air lines from relay valve.
Remove mounting bolts and remove valve.
Mount relay valve with mounting bolts and
lockwashers with exhaust port pointing down.
Connect air lines.
Make sure exhaust port is not restricted.
Make sure new or rebuilt valve is tested as
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
Remove four cover capscrews.
Remove valve cover, piston assembly and piston
spring, if equipped, from valve body.
Remove retaining ring from valve body, using a
snap ring pliers. Then remove washer, exhaust
valve body spring and modulation tube from
Remove O-ring seal from valve body.
Remove capscrew exhaust valve seal and piston
O-ring seal from piston.
diaphragm from exhaust valve body.
Remove O-ring seal, inlet seal retainer and inlet
valve seal from modulation tube.
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