BENDIX LQ-3 LQ-4 FRONT AXLE RATIO VALVE User manual

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®
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-
tionpressuretotheactuatorsduringnormalservicebraking.
Limiting application pressure reduces the braking effort at
thefoundation brakes onthe steering axle.The supply and
deliveryportsin both theLQ-3™andLQ-4™valvesare iden-
tifiedwith embossed lettering.Theports intheLQ-3™valve
are 1/4 inch N.P.T. and in the LQ-4™valve, 3/8 inch N.P.T.
Theexhaustportisnotthreadedineither valve.Twomount-
ing holes are provided for 5/16 inch mounting bolts. Note:
When mounted on the vehicle the exhaust port should be
pointeddown.
GENERAL OPERATION
ThesupplyportoftheLQ-3™orLQ-4™valveisconnectedto
thedeliveryportoftheservicebrakevalve.Thedeliveryport
of the LQ-3™valve is connected to the service port of the
frontaxlerelayvalveortheadaptivebraking modulator.The
LQ-4™valvemaybeused tooperatebrake chambers upto
Type 24 without relay or QRV.
Pressuredeliveredtothe LQ supplyportisreducedby 50%
asitpassesthrough the valveandoutthedelivery port. The
50%reductionoccursonlywhenbrakeapplicationpressure
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
supplyport arereduced by lessthan 50% andapplications
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
LQdeliveryport.
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

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BRAKE
CHAMBER RESERVOIR
TYPICAL LQ-3™FRONT AXLE RATIO VALVE INSTALLATION
BRAKE
CHAMBER
BRAKE
CHAMBER RESERVOIR
LQ-3™
VALVE
BRAKE
CHAMBER
TEE
LQ-4™
VALVE
TYPICAL LQ-4™FRONT AXLE RATIO VALVE INSTALLATION
FIGURE 3 - LQ-3™* BRAKE VALVE APPLICATION: 0-40 PSI
(*LQ-4™VALVE OPERATION SAME AS LQ-3™VALVE.)
Note: The pressures used here are examples only. Both
the LQ-3™and LQ-4™valves may have been supplied with
initialhold-off pressuresof either4 psior 10psi and equal-
ization pressures of 60 or 65 psi respectively depending
uponthe vehicleinstallation andmanufacturer’s specifica-
tion. The LQ-3™valve hold-off pressure depends on the
inlet-exhaust valve spring installed. The LQ-4™valve by
whetheror nota hold-off springis installedunder the lower
piston.
OPERATION — BRAKE APPLICATION OF 40
PSI OR LESS
Whenaservicebrakeapplicationoflessthan 40psiismade,
applicationair enters theLQ valve supplyport andexertsa
force over the surfaces of the outer and inner pistons.
Because of the spring force beneath the outer piston, only
the inner piston moves. The initial delivery of air from the
brakevalveforcestheinnerpistonallthewaydownasshown
in Figure 3. Delivery pressure builds up under the inner
piston as shown in Figure 4 and as explained under
Operation—Balanced.
OPERATION — BALANCED
Air pressure present at the delivery port of the LQ-3™or
LQ-4™valveis also presentbeneaththeinnerpiston. When
the air pressure acting on the underside of the inner piston
isapproximately half ofthebrake valve deliveredpressure,
thepistonlifts, closing theinlet.Theexhaustremainsclosed.
(SeeFigure4.)
SUPPLY
DELIVERY EXHAUST
INLET & EXHAUST
VALVE
INLET & EXHAUST
VALVE RETURN
SPRING
INNER PISTON
OUTER
PISTON
OUTER
PISTON
RETURN
SPRING
FIGURE 2 - TYPICAL INSTALLATIONS
E-6™/E-7™
BRAKE
VALVE
E-6™/E-7™
BRAKE
VALVE
MODULATOR
OR RELAY
VALVE

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FIGURE 6 - LQ-3™FRONT AXLE RATIO VALVE* BRAKE
VALVE APPLICATION AT 60 PSI OR GREATER.
(*LQ-4™VALVE OPERATION SAME AS LQ-3™VALVE.)
FIGURE 4 - LQ-3™FRONT AXLE RATIO VALVE*
BALANCED BRAKE VALVE APPLICATION AT 40 PSI OR
LESS. (*LQ-4™VALVE OPERATION SAME AS LQ-3™VALVE.)
Note:Thetopsurfaceof the inner pistonhasapproximately
onehalf ofthe area ofthe lowersurfaceof the innerpiston.
Air pressure acting on the top surface of the inner piston
exerts a force one half as great as the same air pressure
acting on the lower surface. Therefore, to balance the pis-
ton, (both inlet and exhaust closed) the pressure beneath
theinnerpistonmay be 1/2thataboveit.Anexamplewould
be:30 psi deliveredto the supplyport and actingon the top
surfaceof the innerpiston would resultinapproximately 15
psi at the delivery port and acting on the lower surface.
OPERATION — EXHAUST
Whentheservicebrakeapplicationisreleased,theairabove
the inner piston of the LQ valve returns to the brake valve
andisexhausted.Theairpressureat the delivery portof the
LQvalveactsontheundersideofthe inner piston and liftsit,
whichunseatsthe exhaust valve.(SeeFigure5.) The deliv-
ery volume air exhausts both through the brake valve and
out the exhaust port.
OPERATION — SERVICE BRAKE APPLICATION
40 PSI OR GREATER
When a service brake application of greater than 40 psi is
made, air entering the supply port forces the outer piston
into contact with the inner piston against the resistance of
theouter pistonreturn spring. Boththe outerand inner pis-
tonsnow move asone.Because oftheadded surface area
ofthe outerpiston,delivery pressurefrom the LQvalve will
FIGURE 5 - LQ-3™FRONT AXLE RATIO VALVE* EXHAUST.
(*LQ-4™VALVE OPERATION SAME AS LQ-3™VALVE.)
EXHAUST INLET & EXHAUST
VALVE
INLET & EXHAUST
VALVE RETURN
SPRING
INNER PISTON
SUPPLY
DELIVERY
OUTER
PISTON
OUTER
PISTON
RETURN
SPRING
EXHAUST INLET & EXHAUST
VALVE
INLET & EXHAUST
VALVE RETURN
SPRING
INNER PISTON
SUPPLY
DELIVERY
OUTER
PISTON
OUTER
PISTON
RETURN
SPRING
EXHAUST INLET & EXHAUST
VALVE
INLET & EXHAUST
VALVE RETURN
SPRING
INNER PISTON
SUPPLY
DELIVERY
OUTER
PISTON
OUTER
PISTON
RETURN
SPRING
“catch up” at the rate of 2:1 as supply pressure increases
from40-60psi.Anexamplewouldbe:a brake application of
50psiwouldresultindeliverypressureof40psi.Forservice
applications of 60 psi or greater the LQ valve does not re-
ducedeliverypressure. (SeeFigure6.)

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PREVENTIVE MAINTENANCE
Important: Reviewthe Bendix WarrantyPolicybefore per-
formingany intrusivemaintenanceprocedures.Awarranty
maybevoided if intrusivemaintenanceisperformed during
thewarrantyperiod.
No two vehicles operate under identical conditions, as a
result,maintenanceintervalsmayvary.Experience isavalu-
ableguide in determiningthe best maintenanceinterval for
air brake system components. At a minimum, the valve
shouldbeinspectedevery6monthsor1500operatinghours,
whichevercomes first,forproperoperation.Shouldthevalve
notmeet theelements of theoperational testsnoted in this
document,furtherinvestigationandserviceofthevalvemay
berequired.
SERVICE CHECKS
OPERATIONAL CHECKS
1. Install a test gauge or gauge of known accuracy in the
supplyand delivery linesofthe LQ valve.
2. Build system air pressure to governor cut-out, turn off
engineand apply parkingbrakes.
3. Whilemakingaslowlyincreasing service brake applica-
tion, note that the pressure registered on the gauge
installedinthedeliverylinefromthe LQ valve is approxi-
matelyhalf thepressure registeredon the gauge in the
FIGURE 7 - LQ-4™FRONT AXLE RATIO VALVE
HOLD OFF
SPRING
(11)
BODY (2)
INNER PISTON (3)
O-RING (8)
OUTER
PISTON
SPRING (5)
O-RING (7)
OUTER
PISTON (4)
O-RING (6)
COVER
(1)
INNER
PISTON
SPRING
(9)
INLET
EXHAUST
VALVES
(10)
supply line. The 50% reduction will occur while supply
line pressure is between 0 and 40 psi.
4. When the supply line pressure exceeds 40 psi, but is
below 60 psi, observe that the delivery line pressure is
nolonger onehalf and that the delivery line pressure is
“catching up” to supply pressure.
5. When supply pressure exceeds 60 psi note that the
deliveryline pressure isapproximately equal.
Note: The pressures stated here are examples only.
Various piece numbers of the LQ valves may have
differentpressuresettings.For information onaspecific
installation,consult the vehiclehandbook.
LEAKAGE CHECKS
Make and hold a service brake application. Apply a soap
solution to the exhaust port and around the seam between
thecoverandthebody.Leakageequivalenttoa1"bubblein
5 seconds is permissible.
IftheLQvalvedoes not function as described aboveorleak-
age is excessive, it is recommended that it be returned to
the nearest Bendix authorized outlet for a factory remanu-
facturedvalveundertheExchangePlan.Ifthisisnotpossible,
thevalvecanberepairedwithgenuineBendixparts,inwhich
casethefollowing should provehelpful.
Note: Maintenancekits for theLQ-3™and LQ-4™frontaxle
ratiovalvesareavailablefromanyauthorized Bendix outlet.
REMOVAL
Apply the vehicle parking brakes. Identify and disconnect
the supply and delivery lines of the LQ valve. Remove the
twomounting bolts securingthe LQvalve to thevehicle.
DISASSEMBLY
1. Priortoremovingthe four Phillipsheadscrewsandtheir
lockwashers which secure the cover to the body, mark
therelationship between thecover and thebody.
2. Carefullyseparatethecover(1)(Figure7)fromthebody
(2)and remove theinner (3) andouter pistons (4).(The
cover is under approximately 30 pound load from the
outerpiston spring.)
3. Removetheouter pistonspring(5).
4. Separatethe innerandouter pistons.
5. Removethe o-ring (6)fromthe outer piston.
6. Removethelarge(8) and small(7)diametero-ringfrom
theinner piston.
7. (LQ-4™valve)Removetheinletexhaustvalvespring (9)
and inlet exhaust valve (10) from the inner piston.
Removethehold-offspring (11)ifpresent
8. (LQ-3™valve—Figure8)Removethe retaining ring (1),
washer (2), inlet exhaust valve spring (3), and inlet
exhaustvalve(4).

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7. Placethe cover overthe bodyinthe properposition, as
marked in Step 1 of the Disassembly procedure.
8. Using the four Phillips head screws and lockwashers,
secure the cover to the body. Torque the screws to
50-80inchpounds.
TESTING THE REBUILT LQ-3™AND LQ-4™
FRONT AXLE RATIO VALVE
Test the rebuilt LQ-3™or LQ-4™front axle ratio valve by
performingtheoperationaland leakage testsoutlinedinthe
Service Checks section of this manual.
WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURYOR 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
enginebeinoperation,EXTREMECAUTIONshould
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. Useonly 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 theairpressurefrom
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
recommendedprocedures,deactivatetheelectrical
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.
8. Use only genuine Bendix®replacement parts,
components and kits. Replacement hardware,
tubing, hose, fittings, etc. must be of equivalent
size, type and strength as original equipment and
be designed specifically for such applications and
systems.
INLET-EXHAUST
VALVE (4)
WASHER
(2)
RETAINING
RING
(1)
INLET
EXHAUST
SPRING (3)
FIGURE 8 - LQ-3™FRONT AXLE RATIO VALVE INNER
PISTON ASSEMBLY
CLEANING AND INSPECTION
1. Wash all metal parts in mineral spirits and dry them.
2. Inspectall parts forexcessive wear ordeterioration.
3. Inspectthe valve seatfor nicksor burrs.
4. Check the spring for cracks or corrosion.
5. Replace all rubber parts and any part not found to be
serviceableduring inspection,usingonlygenuineBendix
replacementparts.
ASSEMBLY
Priortoreassembling the LQfrontaxleratio valve, lubricate
all o-rings, o-ring grooves, piston bores and metal moving
surfaceswithBendix siliconelubricantpiecenumber291126
(DowCorning650-M).
1. (LQ-3™valve — Figure 8) Place the inlet and exhaust
valve (4), valve spring (3), and washer (2) in the inner
piston.Install the retainingring(1) inthepiston, making
certain it is completely seated in its groove.
(LQ-4™valve — Figure 7) Place the inlet and exhaust
valve(10)andspring(9)intheinnerpiston(3).Thespring
must be carefully located under the shoulder in the
innerpiston.
2. Install the large (8) and small (7) diameter o-rings in
theirgrooves on theinner piston.
3. Install the o-ring (6) on the outer piston.
4. Insert the inner piston into the bore of the outer piston.
Note: See Figure 7 for proper inner and outer piston
configurationafterassembly.
5. Place the outer piston spring (5) in the valve body and
thehold-offspring(11) ifused.
6. Install the inner and outer piston assembly in the body
throughthe spring (seeFigure 7).

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9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
not attempt repairs requiring machining or welding
unless specifically stated and approved by the
vehicle and component manufacturer.
10. Prior to returning the vehicle to service, make
certainallcomponentsandsystemsarerestoredto
their proper operating condition.

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8BW1573 © 2004 Bendix Commercial Vehicle Systems LLC All rights reserved. 4/2004 Printed in U.S.A.