1
®
SD-03-3410
DESCRIPTION
The VM-3
™
is a control manifold serving as a manifold unit
for air passages between cab and engine compartment and
housing a double check valve and PR-4
™
pressure protection
valve.
OPERATION
1. The double check valve receives supply air from the rear
(primary) supply system, through port No. 3 on Fig. 1,
and front (secondary) supply system, through port No.
1 on Fig. 1, and delivers whichever is higher in pressure
to the spring brake system and through another port to
the trailer supply through the dash mounted PP-7
™
tractor
protection control valve.
2. The PR-4
™
pressure protection valve receives supply air
from the front (secondary) supply port and supplies
protected air to three ports, one on the engine side and
two on the cab side. The PR-4
™
valve will deliver air to
these ports only after the front supply system has built
up to at least 60 psi.
3. Supply air for the trailer control hand valve is taken from
a port inside the cab supplied from the rear (primary) air
supply.
The location and function of the various ports are shown in
Fig. 1 for the engine side of the VM-3
™
manifold and in Fig.
2 for the cab side. The chart shown on Fig. 1 explains the
purpose and function of each port on the engine side and
the chart shown on Fig. 2 the cab side.
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.
Bendix
®
VM-3
™
Firewall Manifold
FIGURE 1 -
ENGINE SIDE
NO.1
NO.4
NO.2
NO.3
NO.9
NO.8
NO.7
NO.6
NO.5
