2
OPERATION
To describe the operation, we shall assume that the low
pressureindicator isset for 60psi. Whenair pressure atthe
supply port and under the diaphragm is above 60 psi, the
electrical contacts remain open because the force exerted
by air pressure underneath the diaphragm overcomes the
forceexerted by thespring above thediaphragm.
Whenairpressure belowthediaphragmdropsbelow 60psi,
the spring exerts a force which is greater than the force
exertedbytheairpressurebelowthediaphragm.Thiscauses
the diaphragm (and the piston in the LP-3™indicator) to
move and allow the electrical contacts to close. This
completes or closes the electrical circuit to the warning
device,warning thedriverof lowairpressure inthesystem.
PREVENTIVE MAINTENANCE
Important: Review the Bendix Warranty Policy before
performinganyintrusivemaintenanceprocedures.Awarranty
maybe voidedifintrusive maintenanceis performed during
thewarranty period.
No two vehicles operate under identical conditions; as a
result, maintenance intervals may vary. Experience is a
valuableguideindeterminingthebestmaintenanceinterval
for air brake system components. At a minimum, the low
pressure indicator should be inspected every 6 months or
1500 operating hours, whichever comes first, for proper
operation. Should the low pressure indicator not meet the
elements of the operational tests noted in this document,
furtherinvestigationandserviceofthevalvemayberequired.
TESTING FOR SERVICEABILITY
OPERATING TEST
1. If possible, determine the setting of the low pressure
indicatorbyreferringtothelabelonthevalveorthevehicle
manual.
2. Operationof thelow pressureindicator maybe checked
withignitionswitch“on”byreducingthesystempressure
and observing that low pressure warning occurs when
system pressure drops below the setting of the low
pressure indicator. The contacts will be closed when
thewarningdeviceoperates.Ifthesettingofthe indicator
is unknown, the contacts should close between
approximately 70 psi and 50 psi.
LEAKAGE TEST
1. With air pressure present at the supply port, coat the
indicatorwith soap solution. No leakage permitted.
REMOVING
1. Block the wheels. Otherwise, secure the vehicle with
otherthan service brakes.
2. Theignition switch should be in the “off” position.
3. Drain the air from the system.
4. Disconnecttheelectricalconnectionsatthelowpressure
indicator.
5. Disconnect the air line and mounting bolts or unscrew
the Indicator from the fitting and remove.
INSTALLING
1. Installin a convenientlocationfor servicing.
2. Connectto areservoirpressurelineatahigh pointin the
systemfor adequatedrainage.
3. If installing an LP-2™indicator, use a supply line of 1/4
O.D.minimum.
4. Connectthe Indicatorterminalsinserieswith theignition
switch and the warning device.
DISASSEMBLY
NOTE: It is generally recommendedthatthe low pressure
indicator, if faulty, be replaced with a new unit;
however,service partsare available;andif repairs
arenecessary,the following will apply:
LP-2™indicator.Unscrew the cover retainerfromthe body.
Removecoverandremovespringanddiaphragmassembly.
LP-3™indicator. Remove cover screws, lockwashers.
Remove cover, contact disc, spring, and shim(s). (Note:
Shimsmayormaynotbepresent.)Removecontactplate,
gasket,piston, and o-ring diaphragm.
CLEANING AND INSPECTION
1. Clean all metal parts in mineral spirits and dry them
completely.
2. Inspect all parts for excessive wear or deterioration.
Checkthe valve spring forcracksor corrosion.
3. Inspectcontact points.If contact pointsare notseverely
pitted, they can be dressed with a fine file.
Replace all parts that were discarded and any parts not
foundtobeserviceableduringinspection,usingonlygenuine
Bendixreplacement parts.
ASSEMBLY
NOTE: When using pipe thread sealant during assembly
andinstallation, take particular care to prevent the
sealant from entering the valve itself. Apply the
sealantbeginningwith thesecondthread backfrom
theend.
LP-2™INDICATOR
1. Placeand positionthe diaphragmassembly inthe body.
Position the spring so that it rests on the upper
diaphragmfollower.
2. Placecoveroverthediaphragmandscrewcoverretainer
to the body and tighten securely. (Torque to 110-130
inchpounds.)
