User's Manual

The primary circuit of the Dual Brake Valve is supplied by No. 1 Reservoir, and the
secondary circuit is supplied by No. 2 Reservoir. Both supply circuits have Low
Pressure Indicators.
The primary service circuit actuates the rear axle service brakes, and supplies the
balance port of the R-7 Modulating Valve. The secondary circuit actuates front axle
Brake Chambers, and supplies the control port of the R-7 Modulating Valve. Either
primary or secondary service circuits will actuate the Stoplight Switch.
Should a service brake application be made while the full spring parking force is applied,
primary circuit air is delivered to the balance port of the R-7 Modulating Valve Double
Check Valve and re-supplies the spring cavities; this reduces the spring force by an
amount equal to the service application and prevents compounding of push rod forces.
To summarize, these systems have the following principal features:
1. During normal operation, the Spring Brake Actuators are held in the released
position by air pressure supplied to the Parking Brake Control Valve and the R-7
Modulating Valve. The Parking Brake Control Valve is supplied from either or both
Service Reservoirs; the two sources of supply air minimize automatic applications.
2. To park the vehicle, the Parking Control Valve is placed in the “Park” position, which
exhausts the air from the Spring Brake Actuators.
3. During normal service braking, air from the two circuits of the Dual Brake Valve is
delivered to the R-7 Modulating Valve and there will be no effect upon the Spring
Brake Actuators. Braking will be through the normal action of air pressure on the
diaphragms of the front, rear and trailer axle Brake Chambers.
4. Should the primary circuit of the Dual Brake Valve fail, there would be no air
pressure to actuate the service brakes on the rear axle, however, the air pressure
delivered by the secondary circuit of the Dual Brake Valve to the R-7 Modulating
Valve would cause the R-7 Modulating Valve to exhaust air from the Spring Brake
Actuators and provide rear axle braking a well as normal service braking to the front
axle and the trailer.
5. Should the secondary circuit of the Dual Brake Valve fail, the primary circuit will
provide normal service brakes to the rear axle and trailer. The Spring Brake
Actuators and Front Axle Brake Chambers will not be actuated.
6. Regardless of which circuit of the Dual Brake Valve might fail or malfunction for any
reason, a signal will be sent back to the trailer because both circuits of the Dual
Brake Valve supply the trailer service line through the Double Check Valves which
are housed in the VM-1 Manifold.
7. The Parking Control Valve, and the PP-3 Tractor Protection Control Valve serves as
a secondary emergency brake control, and can be actuated in the event of treadle
failure.