Air Brake Simulator
Truck and Trailer Air Brake System
Follow compressed air from the compressor to every reservoir, valve, brake chamber and suspension air spring—then operate and diagnose the complete system.
How the complete system works
A tractor-trailer uses stored compressed air for service braking, spring-brake release and suspension. Protective valves divide the system so one failure is less likely to empty every reservoir.
Produce and dry
The engine-driven compressor sends air through the discharge line to the air dryer. The governor controls compressor loading and the dryer purges accumulated moisture at cut-out.
Store and protect
The supply or wet tank receives air first. Check and protection valves feed independent primary and secondary service reservoirs.
Control braking
The dual foot valve meters primary and secondary pressure. Relay and ABS modulator valves deliver reservoir air quickly to the brake chambers.
Release spring brakes
Spring brakes apply mechanically. Air pressure compresses their powerful springs to release the parking brakes.
Supply and parking circuit
The red trailer-supply line fills the trailer reservoir and keeps trailer spring brakes released. Loss of supply pressure causes the emergency portion of the trailer system to apply the spring brakes.
Service control circuit
The blue service line carries a control signal from the tractor. The trailer relay valve uses stored trailer air to apply the trailer service chambers.
Suspension circuit
A pressure-protection valve feeds the suspension only after brake-system pressure is sufficient. Height-control valves add or exhaust air to maintain ride height as load changes.
Spring-brake circuit
Parking control air releases the tractor spring brakes. Removing that pressure allows the chamber springs to apply the brakes. Anti-compounding arrangements prevent unnecessary addition of service and spring forces.
Operate the entire air system
Start the engine, build pressure, release the brakes, connect or disconnect glad hands and change trailer load. Select any labelled component to inspect it.
What happens when pressure or a line is lost?
Blue service line disconnected
The tractor service brakes still operate. The trailer receives no normal service control signal, although its supply reservoir may remain charged through the red line.
Red supply line disconnected
Trailer supply air is removed. The relay-emergency system responds, trailer reservoir pressure falls and trailer spring brakes apply.
Tractor reservoir failure
Separate reservoirs and check valves help preserve the remaining circuit. Low-air warnings alert the driver as pressure falls.
Suspension air bag ruptures
The pressure-protection valve limits loss from the brake system. Suspension height falls while protected brake reservoirs retain usable pressure.
Air-system diagnostic challenge
Generate a hidden failure, operate the vehicle and use the gauges and component inspector before submitting your diagnosis.
Waiting for a diagnostic case
Select “Generate hidden fault” to begin.
Tests and hints reduce the available score.Training references and limitations
The simulator uses generic North American dual-circuit principles described by Ontario’s Official Air Brake Handbook and component-level information published by commercial-vehicle brake manufacturers. It deliberately avoids representing one manufacturer’s exact plumbing. Always consult vehicle-specific service literature.
Ontario Official Air Brake Handbook · Bendix Quick Reference Guide