DEMO - 1965 Ford Truck Shop Manual - ForelPublishing.com

PART 2-7-AIR BRAKES 2-75
PLUNGER
RUBBER SPRING
PISTON
RETURN SPRING
TO BRAKE
CHAMBERS
INLET SEAT
RESERVOIR PRESSURE
EXHAUST PORT
FIG. 2—Foot Control Valve Operation
the exhaust port. Further downward
movement of the piston forces the
inlet-exhaust valve from the inlet
seat (Fig. 2) to open the passage between
the reservoir pressure ports
and the brake chamber ports.
BALANCED POSITION. When
the air pressure in the cavity beneath
the piston and the air pressure being
delivered to the brake chambers
equals the mechanical force on top
of the piston, the piston lifts and the
inlet valve closes, cutting off any
further flow of air from the reservoir
pressure ports through the valve
body. The exhaust Valve remains
closed, however, because the mechanical
pressure at the treadle holds
the piston (seat) down against the
valve. With both valves closed, no
more air can enter and air already
admitted can not escape. The valve
is thus in a balanced position.
If the treadle is depressed further,
mechanical pressure overcomes air
pressure in the cavity beneath the
piston opening the inlet valve again.
This permits more reservoir air to
enter until the pressure below the
piston equals the mechanical pressure
above and the inlet valve closes
again. Complete depression of the
treadle releases full reservoir pressure
to the brake chambers.
TO BRAKE
CHAMBERS
EXHAUST SEAT
INLET EXHAUST
VALVE
RESERVOIR
PRESSURE
EXHAUST
DIAPHRAGM
HI 344-A
RELEASED POSITION. If the
treadle is partially released, air pressure
beneath the piston overcomes
the mechanical pressure above, raising
the piston and the inlet-exhaust
valve assembly. This action closes
the intake valve and opens the exhaust
valve allowing air pressure
from the brake chambers and lines
to be released through the exhaust
port. The air continues to exhaust
until air pressure below the piston
equals the mechanical pressure
above. The foot control valve is
again in balanced position. If the
treadle is allowed to return to the
fully released position, the exhaust
valve remains open to exhaust all
air from the chambers and fully release
the brakes.
Brake Chamber and Slack Adjuster.
Compressed air, admitted to
the brake chamber by the foot control
valve, enters the chamber behind
a diaphragm which forces the
push rod outward (Fig. 12). The outward
movement of the push rod rotates
the slack adjuster which in turn
rotates the brake camshaft and cam
forcing the shoes against the drum.
When the air pressure is released
from the brake chamber, the brake
shoe release springs and the brake
chamber release springs return the
FIG. 3-Hand Control Valve
HIQOQ-A
brake shoes, brake cam, slack adjuster,
and the pushrod and diaphragm
assembly to released position.
Quick Release Valves and Relay
Valve. The quick release valve (Fig.
1) reduces the time required to release
the brakes by hastening the
exhaust of air from the brake chambers.
The valve body contains a
spring-loaded diaphragm so arranged
as to permit supply pressure from
the control valve to flow through
the release valve to the brake chambers
in one direction. When supply
pressure is reduced, the air, which
has passed through, is permitted to
escape rapidly through the exhaust
port.
The quick release valve is used
with both front and rear brake chambers,
or with front chambers only as
in the case of a T-Series truck.
On a T-Series truck, the relay
valve is used in place of the rear
quick release valve (Fig. 20). The
relay valve functions somewhat the
same as the quick release valve, except
that it services four rear brake
chambers on a T-Series truck instead
of two. The relay valve is also more
sensitive to the action of the control
valve in that it can assume a balanced
position as well as apply and
release.
TRACTOR-TRAILER AIR BRAKE
SYSTEM
Tractor-trailer air brake equipment
is available as a regular production
option. The following items
are included in the package.
HAND CONTROL VALVE
The hand operated brake application
valve (Fig. 3) is mounted on the
steering column. It controls the application
of the trailer brakes independent
of the tractor brakes.