Bendix Commercial Vehicle Systems MC-12 MODULATOR CONTROLLER ASSY - Manual (Page 4)

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BALANCED POSITION: Normal Service Application
The modulator reaches a balanced position when control
pressure acting upon the top side 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
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-12 ™
controller senses wheel lockup, it will command the antilock
system to alter the service brake application.
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
1. Every 3 months; 25,000 miles; or 900 operating hours
perform SERVICE CHECKS.
2. Every twelve months; 100,000 miles; or 3600 operating
hours, disassemble the relay valve portion of the M-12
Modulator and clean parts with mineral spirits. DO NOT
DISASSEMBLE THE SOLENOID ASSEMBLY. Replace
all rubber parts and any parts worn or damaged. Check
for proper operation before placing vehicle in service.
FIGURE 5 - BALANCED POSITION: NORMAL SERVICE APPLICATION
TRAILER
CONTROL
DOUBLE
CHECK
BRAKE
VALVE
CONTROL
PISTON
DELIVERY
EXHAUST
SUPPLY
EXHAUST
SOLENOID
SUPPLY
SOLENOID
SERVICE BRAKE
CHAMBER