Chevrolet 70 1969 Series, Shop Manual

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BRAKES 5B-30
Figure 8 -Relay Valve and Air Tank Installed (Typical)
Standard air tank on conventional models is a
divided tank ■which incorporates a wet tank and a
dry tank in the same assembly, divided by a check
valve which is built into the tank.
The purpose of the air tanks is to provide a
place to store compressed air so there will al­
ways be an ample supply available for immediate
operation of the brakes. Tanks provide storage for
sufficient compressed air for several brake ap­
plications with engine stopped.
Another purpose of the air tanks is to provide
a place where the air, heated during compression,
can cool and the water vapor can condense. Most
of this condensation takes place in the "wet" tank;
this is the tank into which the compressed air is
first discharged from the compressor. Condens­
ation should be drained from all air tanks daily.
To drain tanks properly, leave drain cocks open
until all air escapes and draining stops. Daily
draining is not necessary on those models which
have the optional moisture ejector valve.
All pressure for operation of the brakes and
air compressor governor is taken from the dry
tank. A one-way check valve at inlet to second tank
prevents loss of air pressure from the second tank
in the event of leakage in the first tank or air com ­
pressor discharge line. On tandem axle models, a
third air tank or a larger tank is used to provide
sufficient volume of air for the additional brake
chambers. All air lines are interconnected in a
manner similar to the single axle models.
Air tank U-bolts and support bracket to frame
bolts should be checked for looseness at regular
intervals and tightened if necessary. Air tank may
be cleaned inside using steam or hot water. If cor­
rosion or other damage has weakened the tank, it
must be replaced.
AIR TANK CHECK VALVE
One-way check valve is installed at inlet to
second air tank on tilt cab models. Check valve
prevents loss of air pressure from second air
tank in the event of leakage in the first tank or in
the air compressor discharge line. Arrow on
valve body indicates direction of air flow through
valve.
Check valve should be removed, disassembled,
and cleaned at regular intervals. The rubber valve
seat should be replaced if there is any evidence of
deterioration or hardening. Valve spring should be
replaced if weakened by rust or corrosion. Valve
disc should be perfectly smooth and free of rust or
corrosion. When installing check valve, make sure
it is installed to permit air flow from first tank
into second tank as indicated by the arrow on valve
body.
On conventional models the check valve is built
into the air tank at the point where the tank is di­
vided. This type check valve is a spring-loaded
valve and functions the same as the other one-way
check valve. The valve is accessible by removing
the valve cap from the air tank. Use caution when
CHEVROLET SERIES 70 -8 0 H EAVY DUTY TRUCK SH O P M A N U A L