Bendix Commercial Vehicle Systems R-7 MODULATING VALVE - Manual (Page 3)

3
OPERATION - SERVICE APPLICATION WITH LOSS OF
AIR IN SECONDARY CIRCUIT (FIGURE 6)
A service application made with a loss of air in the secondary
circuit would result in less or no air delivered to the top of
the control piston; however, the piston would not move and
braking on the rear axle(s) is assured because the primary
circuit supplies rear axle service brakes. The spring brake
actuators will not be actuated.
OPERATION - PARKING (FIGURE 7)
When the handle of the parking control valve is placed in the
“park” (exhaust) position, the modulating valve’s supply air
pressure and the air pressure in the spring brake actuator
cavities is exhausted. The single check valve speeds the
exhaust of air from the actuator cavities by allowing the air
on top of the balance piston to exhaust by the double check
valve through the supply port to atmosphere. When air
pressure drops sufficiently, the balance piston opens the
inlet valve thus opening the larger passage in the modulating
valve insuring rapid exhaust of the balance of air pressure in
the spring cavity of the spring brake actuator.
SERVICE TESTS
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO
AVOID
PERSONAL INJURY OR DEATH:
When working on or around a vehicle, the following
general precautions should be observed at all times.
1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.
2. Stop the engine and remove ignition key when
working under or around the vehicle. When
working in the engine compartment, the engine
should be shut off and the ignition key should be
removed. Where circumstances require that the
engine be in operation, EXTREME CAUTION should
be used to prevent personal injury resulting from
contact with moving, rotating, leaking, heated or
electrically charged components.
3. Do not attempt to install, remove, disassemble or
assemble a component until you have read and
thoroughly understand the recommended
procedures. Use only the proper tools and observe
all precautions pertaining to use of those tools.
4. If the work is being performed on the vehicle’s air
brake system, or any auxiliary pressurized air
systems, make certain to drain the air pressure from
all reservoirs before beginning ANY work on the
vehicle. If the vehicle is equipped with an AD-IS
™
air dryer system or a dryer reservoir module, be
sure to drain the purge reservoir.
5. Following the vehicle manufacturer’s
recommended procedures, deactivate the
electrical system in a manner that safely removes
all electrical power from the vehicle.
6. Never exceed manufacturer’s recommended
pressures.
7. Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove a
component or plug unless you are certain all
system pressure has been depleted.
8. Use only genuine Bendix ® replacement parts,
components and kits. Replacement hardware,
tubing, hose, fittings, etc. must be of equivalent
size, type and strength as original equipment and
be designed specifically for such applications and
systems.
9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
not attempt repairs requiring machining or welding
unless specifically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certain all components and systems are restored
to their proper operating condition.
SECONDARY
SERVICE
CIRCUIT
CONTROL
PORT
EXHAUST
PORT CONTROL
PISTON DUAL BRAKE
VALVE
PRIMARY SERVICE
CIRCUIT
BALANCE
PORT
DOUBLE
CHECK VALVE
SUPPLY
PORT
PARK
CONTROL
VALVE
SINGLE
CHECK
VALVE
BALANCE PISTON
INLET/EXHAUST
VALVE
SPRING
BRAKE
ACTUATOR
+ SPRING BRAKE HOLD-OFF PRESSURE
- SERVICE AIR PRESSURE
o ATMOSPHERE PRESSURE
#2 RES.
#1 RES.
PRIMARY -
SECONDARY -
PARK -
FIGURE 7 - PARKING
PREVENTIVE MAINTENANCE
Important: Review the Bendix Warranty Policy before
performing any intrusive maintenance procedures. A warranty
may be voided if intrusive maintenance is performed during
the warranty period.
No two vehicles operate under identical conditions, as a
result, maintenance intervals may vary. Experience is a
valuable guide in determining the best maintenance interval
for air brake system components. At a minimum, the R-7
™
valve should be inspected every 6 months or 1500 operating
hours, whichever comes first, for proper operation. Should
the R-7
™ valve not meet the elements of the operational
tests noted in this document, further investigation and service
of the valve may be required.