2
BVA-85
™
MID
REAR
TO ACCESSORIES
BA-922
®
TWIN CYLINDER
COMPRESSO R
AD-IS EP
EXTENDED PURGE
AIR DRYER
PP-D C
™
PUSH-PULL VALVE WITH
INTEGRAL DOUBLE CHEC K
RA M
REAR AXLE MODULE
FAM
FRONT AXLE
MODUL E
ABS-6
WITH
TRACTION CONTROL
DOOR
INTERLOCK
VALVE WITH
CONTROL
MODUL E
DUAL
RELAY VALVE
FRONT
Secondary
Control
Primary
Control
System Normal
With the system normal and air pressure available in all
service reservoirs, brake application pressure is transmitted
from the primary and secondary circuits of the foot brake
valve.
Application pressure is transmitted simultaneously to the
front and mid-axle brakes and to the primary and secondary
control ports of the Dual Relay Valve. The Dual Relay Valve
applies or releases the rear axle brakes in direct proportion
to the control signals received from the foot brake valve.
The brake on each axle are applied using pressure from
their dedicated respective reservoirs.
Loss of Front Axle Service Reservoir
A service application made with a loss of air in the
secondary circuit results in a no or low application of the
front axle brakes. Air pressure from the primary circuit of
the foot brake valve applies the mid-axle brakes and enters
the primary control port of the Dual Relay Valve. The Dual
Relay Valve responds to primary control and applies the
rear axle brakes. Brake release occurs when foot brake
valve pressure is removed.
Loss of Mid-Axle Service Reservoir
A service application made with a loss of air in the primary
circuit results in a no or low application of the mid-axle
brakes. Air pressure from the secondary circuit of the foot
brake valve applies the front axle brakes and enters the
secondary control port of the Dual Relay Valve. The Dual
Relay Valve responds to secondary control and applies the
rear axle brakes. Brake release occurs when foot brake
valve pressure is removed.
Loss of Rear Axle Service Reservoir
With a loss of rear axle service pressure, the front and
mid-axle brakes will be applied by the foot brake valve.
Primary and secondary control pressure is received by the
Dual Relay Valve however, a no or low application of the
rear brakes will occur due to a loss of pressure in the rear
service reservoir. Front and mid-axle brakes will release
when foot brake valve pressure is removed.
PREVENTIVE MAINTENANCE
GENERAL
Important: Preventive maintenance for the Dual Relay
Valve consists entirely of inspections and tests. The Dual
Relay Valve is not serviceable and must be replaced when
testing or inspection warrants it. Kits and replacement parts
are not available.
Because no two vehicles operate under identical
conditions, maintenance and maintenance intervals will
vary. Experience is a valuable guide in determining the best
maintenance interval for any one particular operation.
Perform the tests and inspections presented at the
prescribed intervals. If the Dual Relay Valve fails to function
as described or leakage is excessive, it must be replaced
with a genuine Bendix unit, available at any authorized
parts outlet.
Every 3 months, or 25,000 miles or 900 operating
hours:
1. Remove any accumulated contaminants and visually
inspect the exterior for excessive corrosion and
physical damage.
FIGURE 2 - TYPICAL ARTICULATED COACH SCHEMATIC
