SPRING BRAKE CONTROL VALVE
The spring brake control valve is a manually
operated valve of push-pull type. When the valve is
pushed "in" the valve is open to supply air. The "out"
position closes off supply air and allows delivered air to
exhaust to atmosphere, applying the spring brakes.
arrangement which provides automatic return to "out"
position when brake system air pressure approaches low
Fig. 1 Spring Brake Control Valve
The spring brake control valve serves to apply and
release the spring actuated parking brakes. The valve is
in the "in" position under normal operation on either a
straight truck or tractortrailer. Air supply passes through
the valve delivering system pressure to retract and hold
parking brakes in released position. Manual pull "out"
closes off air supply and vents delivered air to
atmosphere, applying the parking brakes.
When valve is pushed "in," it will remain in as long as
supply line is 48-241 kPa (7-35 psi) or more. During
normal operation the air control valve will automatically
apply, moving "out," if air pressure should drop to 48-241
kPa (7-35 psi). The automatic application will result when
both primary and secondary systems have depleted air
supply to 48-241 kPa (7-35 psi).
Refer to Fig. 2 for following operational description.
Fig. 2 illustrates valve in applied (out) position.
Pushing piston in moves valve assembly off body
seat until contacting end cap seat. Air pressure at inlet
has free passage to outlet and is blocked from
exhausting to atmosphere.
Pulling piston out moves valve assembly away from
end cap seat and contacts body seat. Air pressure at
inlet is blocked from entering either outlet or exhaust
passages. Air pressure in outlet has free passage to
exhaust to atmosphere.
The spring in the valve assists to move piston out
automatically if inlet pressure drops and effective
opposing force across the valve seat is overcome.
Fig. 2 Cross Section of Spring Brake Control Valve
11 "O" Ring
12 Snap Ring
to 12 to 17
Once each year or every 160,000 km (100,000
miles) the valve should be removed, disassembled and a
repair kit installed.
Use air pressure source equipped with in-line
manual shut-off valve, air gauge known to be accurate
and connection. Connect air source to
CTS-4079 - CHAPTER VII - Page 3