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GROUP 2-BRAKES
the counter force reacts through the
valve plunger, valve operating rod,
and pedal linkage against the driv-
er's foot. This reaction force is in
direct proportion to the hydraulic
pressure developed within the brake
system.
HOLDING POSITION
'
During brake application, the "re-
action" force which opposes the
force applied by the driver, tends to
close the atmospheric port. When
both atmospheric and vacuum ports
are CLOSED, the booster is said to
be in the holding position. With both
valves closed, any degree of brake
application attained will be held un-
til either the atmospheric port is
reopened by an increase
,
in pedal
C PORT OPEN
pressure to further increase the brake
application or by a decrease in pedal
pressure to reopen the vacuum port
PRESSURE
to decrease the brake application.
Whenever the pressure applied to
"1326-A
the brake pedal is held constant for a
moment, the valve returns to its
holding position. However, upon
plunger move to the left in the power
and the valve plunger in proportion
the
position
diaphragm assembly to compress the
to their respective contact areas. The
the
the brake pedal
valve return spring and bring the
pressure acting against the valve
overmles the reaction force- In this
poppet valve into contact with the
plunger and valve operating rod
position the valve plunger and at-
vacuum valve seat in the valve hous-
tends to move the valve plunger
mospheric
seat are held
ing to " C L O S E the vacuum port.
slightly
to
the right in relation to
from the valve Poppet to admit maxi-
Any additional movement of the
the diaphragm and valve housing
mum atmosphere Pressure to the rear
valve operating iod in the applied di-
assembly to close off the atmospheric
(right) chamber. With the
rection moves thevalve plunger away
port. The driver is thus assured a
(left) chamber open to manifold
from the poppet valve to "OPEN"
"feel" of the brake, since part of
vacuum, full power application, is
the atmospheric port and admit
atmosphere through the air cleaner
and
passages
in
the
diaphragm
plate to the right side of the power
chamber. With vacuum present on
the left side of the diaphragm and
VACUUM PORT
-
valve housing and atmospheric pres-
sure present on the right side of the
ATMOSPHERIC SOURCE
diaphragm, a force is developed to
move the vacuum power diaphragm
,
assembly, hydraulic push rod and
hydraulic piston to the left to close
the compensating port and force hy-
draulic fluid under pressure through
-
the residual check valve and brake
tubes into the brake wheel cylinders.
As hydraulic pressure is developed in
the hydraulic cylinder, a counter
force (to the right) acting through
the hydraulic push rod, sets up a re-
action force against the vacuum
power diaphragm and valve plunger
through the rubber reaction disc (lo-
cated at the end of the hydraulic
push rod). The rubber reaction disc
acts similar to a column of fluid to
distribute the pressure between the
H
1 3 2 7 - ~
vacuum power diaphragm assembly
FIG.
5-Booster in Holding Position
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