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INLET SOLENOID
RESERVOIR
FIGURE 4 - BALANCED POSITION
which passes through the open inlet solenoid and into the
control cavity of the relay valve. The valve then applies air to
the service brake chambers in proportion to the control signal.
If wheel lock is impending, the EC-11
commands the solenoids to modulate brake chamber
pressure on the axles in which the system is installed.
OPERATION
APPLYING: Normal Service Application
When a normal service brake application is made, control
air pressure from the brake valve enters the modulator
control port. The air passes through the supply solenoid
and acts on the modulator's piston. The piston closes the
modulator exhaust and opens the inlet, delivering supply air
out the delivery ports.
BALANCED POSITION: Normal Service Application
The modulator reaches a balanced position when control
pressure acting upon the topside of the piston approaches
that of the air acting upon the underside of the piston. The
piston moves upward and closes the inlet valve, while the
exhaust remains closed. This prevents the modulator from
delivering or exhausting air.
EXHAUSTING: Normal Service Application
When the brake valve is released, control pressure exhausts
through the supply solenoid and the check valve in the
4
EXHAUST
SOLENOID
SUPPLY
electronic controller
™
BRAKE
VALVE
CONTROL
PISTON
DELIVERY
EXHAUST
solenoid housing and out the exhaust port of the brake valve.
As the piston moves upward, the modulator's exhaust opens,
allowing air from the piston's underside to exhaust through
the modulator exhaust port.
ANTILOCK MODE: Solenoids Activated
If a service brake application is made and the EC-11
controller senses impending wheel lockup, it will command
the antilock system to alter the service brake application
automatically.
When activated, shuttles within the solenoids alter the
application and exhaust of control air pressure. The supply
solenoid closes, preventing control line pressure from
entering the modulator. Then the exhaust solenoid opens,
allowing control pressure to exhaust from the top side of
the piston through the exhaust port of the solenoid assembly.
This activity occurs in a pulsating manner, simulating
"pumping of the brakes."
PREVENTIVE MAINTENANCE
GENERAL
Perform the inspections and tests at the prescribed intervals.
If the MC-11
described, repair or replace the unit.
EVERY 3 MONTHS; 25,000 MILES; 900 OPERATING
HOURS; OR DURING THE VEHICLE CHASSIS
LUBRICATION INTERVAL
DOUBLE
CHECK VALVE
TRAILER
CONTROL
BRAKE
CHAMBER
tractor antilock assembly fails to function as
™
VALVE
™
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