Bendix Commercial Vehicle Systems LQ-4 FRONT AXLE RATIO VALVE User Manual
Bendix, Lq-3, Lq-4
1
®
SD-03-951
FUNCTION AND DESCRIPTION
The LQ-3
™
and LQ-4
™
front axle ratio valve is used on the
front or steering axle of a vehicle to limit the brake applica-
tion pressure to the actuators during normal service braking.
Limiting application pressure reduces the braking effort at
the foundation brakes on the steering axle. The supply and
delivery ports in both the LQ-3
™
and LQ-4
™
valves are iden-
tified with embossed lettering. The ports in the LQ-3
™
valve
are 1/4 inch N.P.T. and in the LQ-4
™
valve, 3/8 inch N.P.T.
The exhaust port is not threaded in either valve. Two mount-
ing holes are provided for 5/16 inch mounting bolts. Note:
When mounted on the vehicle the exhaust port should be
pointed down.
GENERAL OPERATION
The supply port of the LQ-3
™
or LQ-4
™
valve is connected to
the delivery port of the service brake valve. The delivery port
of the LQ-3
™
valve is connected to the service port of the
front axle relay valve or the adaptive braking modulator. The
LQ-4
™
valve may be used to operate brake chambers up to
Type 24 without relay or QRV.
Pressure delivered to the LQ supply port is reduced by 50%
as it passes through the valve and out the delivery port. The
50% reduction occurs only when brake application pressure
to the supply port of the LQ is between 0 psi and 40 psi.
Brake applications between 40 psi and 60 psi to the LQ
supply port are reduced by less than 50% and applications
above 60 psi are not reduced at all. An example would be:
65 psi delivered to the supply port results in 65 psi out the
LQ delivery port.
Bendix
®
LQ-3
™
& LQ-4
™
* Front Axle Ratio Valve
1/4" NPT
PISTON SPRING
HOLD OFF
SPRING
(WHEN REQUIRED)
LOWER PISTON
ASSEMBLY
INLET EXHAUST
VALVE SPRING
1/4" NPT
3/8" NPT
3/8" NPT
LQ-4
™
FRONT AXLE RATIO VALVE*
LQ-3
™
FRONT AXLE RATIO VALVE
FIGURE 1 - LQ-3
™
AND LQ-4
™
FRONT AXLE RATIO VALVE
(*THE LQ-4
™
VALVE'S OPERATION IS IDENTICAL TO THE LQ-3
™
VALVE.
INTERNAL CONFIGURATION IS SLIGHTLY DIFFERENT.)
LQ-3
™
FRONT AXLE RATIO VALVE
EXTERIOR