Must be used whenever two sources of air are used to operate a single device or system. For CDL air brake test, the driver must know there are 2 in the system.
OBSOLETE Independently applies and releases the trailer service brakes. Knowledge Test Question: This air brake control is not to be used for parking. Although most tractors are still equipped with hand valves, beyond a trailer service tug test, these air…
Applies the parking brakes of the air brake equipped vehicle indefinitely – if needed of course. The parking brakes are held in the “ON” position by the mechanical force of the springs; these spring parking brakes are held in the “OFF” position by system air…
OBSOLETE Used on some vehicles with dual air systems. This device provides a means of using the force of the spring brakes to assist in stopping a vehicle in an event of a failure in the rear (primary) air system.
Slack adjusters have three purposes: 1) To convert the forward linear motion of the push rod into rotary motion of the camshaft. The slack adjuster works on exactly the same principle as a box end wrench on a nut. 2) To act as a lever, thus generating greater…
Stores compressed air for braking and for other air operated accessories. The air tanks are the first fail-safe in the air brake system. In the unlikely event that the air compressor fell of the side of the engine, the air tanks (reservoirs) store enough air…
OBSOLETE Fills the trailer air tanks (reservoir) and applies and releases the trailer service brakes. The relay emergency valve also applies the trailer emergency brakes in the event of a trailer breakaway or normal disconnect. Knowledge Test Question: In the…
OBSOLETE To reduce application pressure to the steering axle by 50 % compared to the drive axle brakes, when required by reduced road conditions (rain, snow or ice). The system consists of a dash switch with 2 positions: Dry Road: 100% front wheel braking; in…
MUST KNOW The brake pedal applies the service brakes - truck, or truck and trailer brakes. In other words, the brake pedal brings the vehicle to a stop when it it depressed. SHOULD KNOW The foot valve operates the secondary and primary sub systems…
To stop the vehicle, brake linings rub against the brake drum. This action creates friction, converting the vehicle's forward energy of motion into heat energy, which stops the vehicle’s tires. If the tires have traction, the vehicle will come to a stop. The…
To reduce application pressure to the steering axle brakes during most braking situations. Reduced pressure to the steer axle brakes occurs for most braking applications. Only during hard braking is there equivalent pressure delivered to both the front and…
The gauges are in either pounds per square inch (psi) or Kilopascals (kPa). These measure the amount of air pressure in the primary and secondary air tanks.
A cattle chute with one-way gates allows the cows to only move in one direction – forward. A one-way check valve in an air brake system works exactly the same – it allows air to only move in one direction – forward through the system. The one-way check valves…
Using the pry bar method, confirm that the brake is in fact out of adjustment. After confirming that the brake is out-of-adjustment and it is equipped with a manual slack adjuster, complete the following steps to bring the brake back into adjustment. If one…
Depending on which province you're in, the air buildup time or compressor test has somewhat different paramenters. Still, all require that the diesel motor be at a fast idle. A fast idle on a diesel engine is between 900 &1200 rpm.
The National Safety Code madates that every driver of a commercial vehicle equipped with air brakes must check push rod travel every day. In many jurisdications, drivers are allowed to use the pry bar method; in others , they must use the applied stroke…
The National Safety Code madates that every driver of a commercial vehicle equipped with air brakes must check push rod travel every day as part of his/her pre-trip inspection. In some jurisdications, drivers must use the applied stroke method; in others, they…