Chevrolet 70 1969 Series, Shop Manual

Page: 239 / 913

BRAKES 5B-46
The inversion valve employs a 1-1/ 4 " diam­
eter hole mounting. The valve serves as a mani­
fold having a total of six (6) 1/ 4 " pipe ports: three
(3) control ports, two (2) delivery ports and one
(1) supply port. These ports are identified. The
control ports are marked " C ," supply " S " and the
delivery ports are marked " D ." The exhaust port
is protected by a diaphragm.
INVERSION VALVE OPERATION
With no air pressure in the system, the in­
version valve inlet valve is open and its exhaust
is closed. On initial build-up, as air enters the
parking reservoir to which the inversion valve
supply port is connected, it will pass by the open
inlet and out the delivery ports. When system air
pressure reaches between 50 and 60 psi and the
push-pull control valve is pushed in, air will pass
into the inversion valve from the push-pull control
valve. This air flows in one control port and exerts
a force on the inversion valve piston. At a pres­
sure between 60 and 70 psi, the piston moves
against the resistance of the two (2) piston springs.
The piston exhaust seat moves away from the inlet
and exhaust valve, opening the exhaust passage.
The inlet valve spring and supply air in the inlet
valve will cause it to seat. Air at the inversion
valve delivery will now exhaust from the valve
exhaust port.
PAR KIN G O R E M E R G E N C Y
The air at the inversion valve control ports
is exhausted through the push-pull control valve
exhaust when it is operated. The piston springs
will then cause the piston to move and seat on the
inlet and exhaust valve closing the exhaust pas­
sage. The inlet valve is moved off its seat by the
piston, so that supply air from the parking reser­
voir will pass by the open inlet and out the deliv­
ery ports.
When the application is released by pushing
in on the push-pull control valve, air passes into
the inversion valve control port. The piston moves
away from the inlet and exhaust valve, opening the
exhaust passage through the piston. The inlet valve
closes and air in the delivery ports will exhaust
through the center of piston stem and out the in­
version valve exhaust port.
P R E V E N T IV E M A IN T E N A N C E
The manufacturer recommends that every
year or after 50,000 miles the inversion valve be
disassembled, cleaned and lubricated. Lubricate
with a barium base grease (or equivalent).
Rubber parts should be replaced and any other
parts which show signs of wear or damage should
also be replaced.
INVERSION VALVE
OPERATING AN D LEAKAGE CHECKS
O P E R A T IN G
With the air brake system built up to governor
cut out pressure and the brakes released, operate
by pulling out the push-pull control valve button
to apply the brakes. Note that the brakes apply.
Operate by pushing in the push-pull control
valve to release the brake application and note
that the delivered air from the inversion valve is
exhausted out its exhaust port. The operation of
the push-pull control valve will not necessarily
complete the release of the brakes. A full 100 psi
service brake application after the push-pull con­
trol valve is pushed in should complete the release.
L E A K A G E
Start leakage checks with system pressure up
to governor cut out and brakes released. Check
the inversion valve exhaust port for possible leak­
age at (1) the large piston grommet; (2) piston
stem grommet or; (3) the inlet valve or its seat.
Slight leakage is permissible. While the inversion
valve is still in this position, the cap nut should be
checked for leakage by the seal ring.
Actuate push-pull control valve by pulling out
on the button to apply the brakes, then check the
inversion valve exhaust port for exhaust valve or
seat leakage.
If the inversion valve does not function as
described or leakage is excessive, it is recom­
mended that it be repaired or replaced.
INVERSION VALVE REPLACEMENT
(Refer to Figure 17)
R E M O V A L
1. Block and hold vehicle by means other than
air brakes.
2. Drain service and parking reservoir air
supply.
3. Disconnect air lines and air brake hoses
from inversion valve.
4. Loosen mounting nut and remove valve.
IN S T A L L A T IO N
1. Check and clean air lines to valve.
2. Mount valve securely with mounting nut
and lock washer.
3. Connect air lines and air brake hoses.
4. Check for proper operation and leaks.
PUSH-PULL CONTROL VALVE
DESCRIPTION
The push-pull control valve is located in the
dash panel. It is to the right of the steering col-
CHEVRQLET SERIES 70-80 H EAVY DUTY TRUCK SH O P M AN U AL