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Pressure Indicator is set for 60 psi. When air pressure at
the 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 force exerted by the spring above the
diaphragm.
When air pressure below the diaphragm drops below 60
psi, the spring exerts a force which is greater than the
force exerted by the air pressure below the diaphragm.
This causes the diaphragm (and the piston in the LP-3) to
move and allow the electrical contacts to close. This
completes or closes the electrical circuit to the warning
device, warning the driver of low air pressure in the system.
PREVENTIVE MAINTENANCE
Every six months, 1800 operating hours or 50,000 miles,
check electrical connections. Low Pressure Indicator should
be checked for proper operation by performing Operating
Test as described elsewhere in this sheet.
TESTING FOR SERVICEABILITY
OPERATING TEST
1. If possible, determine the setting of the Low Pressure
Indicator by referring to the label on the valve or the
vehicle manual.
2. Operation of the Low Pressure Indicator may be
checked with ignition switch on by reducing the
system pressure 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 the warning device operates. If the setting
of the 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
indicator with soap solution. No leakage permitted.
REMOVING
1. Block the wheels. Otherwise, secure the vehicle with
other than service brakes.
2. The ignition switch should be in the off position.
3. Drain the air from the system.
4. Disconnect the electrical connections at the Low
Pressure Indicator.
5. Disconnect the air line and mounting bolts or unscrew
the Indicator from the fitting and remove.
INSTALLING
1. Install in a convenient location for servicing.
2. Connect to a reservoir pressure line at a high point in
the system for adequate drainage.
3. If installing an LP-2G Indicator, use a supply line of 1/4
O.D. minimum.
4. Connect the Indicator terminals in series with the ignition
switch and the warning device.
DISASSEMBLY
NOTE: It is generally recommended that the Low Pressure
Indicator, if faulty, be replaced with a new unit;
however, service parts are available; and if repairs
are necessary, the following will apply:
LP-2 Unscrew the cover retainer from the body. Remove
cover and remove spring and diaphragm assembly.
LP-3. Remove cover screws, lockwashers. Remove cover,
contact disc, spring, and shim(s). (Note: Shims may or
may not be present.) Remove contact plate, gasket, piston,
and O-Ring diaphragm.
CLEANING AND INSPECTION
Clean all metal parts in mineral spirits.
Inspect all parts for wear, cracks, or deterioration and
replace all parts not considered serviceable with genuine
Bendix parts.
If contact points are not pitted severely, they can be dressed
with a fine file.
ASSEMBLY
LP-2
1. Place and position the diaphragm assembly in the body.
Position the spring so that it rests on the upper
diaphragm follower.
2. Place cover over the diaphragm and screw cover retainer
to the body and tighten securely. (Torque to 110-130
inch pounds.)
LP-3
1. Lubricate bore of body and both sides of the O-Ring
diaphragm with silicone lubricant BW-650-M (Bendix
piece no. 291126).
2. Install O-Ring diaphragm in body. (Note: O-Ring portion
of diaphragm should face supply port.)
3. Install piston in body. Flat side of piston should face
O-Ring diaphragm.
4. Install gasket. (Always use a phenolic gasket in a two
terminal switch and a metallic gasket in the single
terminal.)
5. Position contact plate over fingers of piston. Contact
plate should rest on face of gasket.
6. If shim(s) are used, place shim(s) in cover.
7. Place spring in cover.
8. Place contact point so that it rests on spring.
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