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LOW PRESSURE INDICATORS
SD-06-1600*
DESCRIPTION
The Low Pressure Indicator is a safety device designed to
give an automatic warning to the driver whenever air
pressure in the air brake system is below the safe minimum
for normal vehicle operation. It is usually used to operate
an electrical buzzer or warning light, or both, which are
audible or visible to the driver.
Two styles of Low Pressure Indicators are currently
manufactured.
The LP-2 Low Pressure Indicator, which is the older style
and consists of a die cast body with a spring loaded
diaphragm clamped between the body and the Bakelite
cover.
The LP-3 Low Pressure Indicator is the newer style,
consisting of a die cast body, nylon cover and employs a
spring loaded O-Ring diaphragm and piston. The LP-3 is
available with either one terminal or two. The single terminal
unit utilizes a metallic gasket between body and case to
ground the lower contract strip. The two terminal unit utilizes
a phenolic insulating gasket to isolate both terminals from
the vehicle frame.
The electrical contacts provided in both the LP-2 and LP-3
indicators remain closed by spring force until the air brake
system pressure below the diaphragm is above the setting
(force) of the Low Pressure Indicator spring. The setting of
the indicator and piece number is marked on a label on the
valve body. If a label is not present, then the vehicle manual
should be consulted for the proper setting. The nominal
setting of the indicator is 60 psi; however, pressure settings
may vary depending upon the vehicle.
OPERATION
To describe the operation, we shall assume that the Low
FIGURE 1 - LP-2 FIGURE 2 - LP-3
COVER
DIAPHRAGM
BODY
SPRING
CONTACT
POINTS
COVER
SPRING
CONTACT
POINTS
PISTON
BODY
O-RING
DIAPHRAGM
*Formerly SD-06-2
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