1
PRIMARY
CONTROL
PORT (41)
CAST PORT
IDENTIFICATION
SECONDARY
CONTROL
PORT (42)
RESERVOIR
SUPPLY
PORT (11)
MOUNTING
BRACKET STUDS
EXHAUST
PORT (1)
DELIVERY
PORT (22)
RESERVOIR
SUPPLY
PORT (11)
Bendix
®
Dual Relay Valve
SD-03-1000
DESCRIPTION
The Dual Relay Valve is a special purpose, multifunction
relay valve. It is typically used on articulated vehicles with
three or more axles. Normally mounted at the rear of the
vehicle, in proximity to the valves and chambers served, its
function is similar to a pilot relay and speeds the application
and release of control air pressure to the service relay
valve(s) on the rear most axle or axles of the vehicle. The
Dual Relay Valve is a pilot relay valve that responds to the
control air delivered to it from both circuits of the foot brake
valve. The Dual Relay Valve is controlled independently
by the front (secondary) and mid (primary) delivery circuits
of the dual circuit foot brake valve.
The Dual Relay Valve is supplied air from the rear axle(s)
service reservoir that is isolated from the other service
reservoirs forming a third service brake circuit on the
vehicle. With the addition of a third brake circuit the vehicle
will maintain braking on at least two axles in the event of a
single service system malfunction. In systems where this
valve is used, the brake circuits are designated as Front
(steering) Axle, Mid-Axle and Rear Axle.
Although typically nipple mounted to the rear service
reservoir the valve can be bracket mounted. Only four (4)
ports are utilized in the die cast body of the Dual Relay
Valve. All air connections are identifi ed with raised numerals
with the following designations:
Port ID
Size
Designation
41
3/8 NPTF
Primary Control Port
42
3/8 NPTF
Secondary Control Port
12, 43
Plugged
Not used
22
3/8
NPTF
Delivery
11
3/8 NPTF
Rear Service Reservoir
OPERATION
Refer to fi gures 1 and 2. Each service reservoir is isolated
and is protected from loss of air in other service reservoirs.
The front and mid-axle service reservoirs supply air directly
to the secondary and primary circuits of the foot brake
valve, as well as antilock and traction components for their
respective circuits. The rear axle service reservoir supplies
air to the Dual Relay Valve, as well as the rear axle service
antilock relay and traction components.
FIGURE 1 - DUAL RELAY VALVE
