Drivers must be alert for air brake system leaks and pressure loss in the air tanks when brakes are not being used. These conditions indicate air loss in the air brake system. For safety, drivers should test the air loss rate of the vehicle’s brake system.
To test the air loss rate of the brake system, release the spring brakes, establish normal air pressure and shut off the engine. Hold the brake pedal in the fully applied position and observe the air pressure readings for one minute.
The pressure will drop noticeably when the brakes are first applied but must not continue to drop at a rate greater than specified in the chart below. The amount of pressure drop that takes place when brakes are first applied is not considered when performing the air loss rate test. The air brake system is defective when air loss exceeds the specified values.
Step-by-step procedure
- Properly secure the vehicle and release the spring brakes.
- Ensure that the air brake system is within its normal operating pressure range. Shut off the engine.
- Press and hold the brake pedal in the fully applied position.
- Note the pressure indicated on the primary and secondary air tank gauges. 5. Note the change in pressure over one minute.
Pass
The vehicle passes the test when the drop in pressure is equal to or less than the value specified for the vehicle.
Fail
The vehicle fails the test when the drop in pressure exceeds the value specified for the vehicle.
Important: The Ontario Highway Traffic Act and regulations prohibit operation of a vehicle with an excessive air loss rate.
| Air Loss Rates | |
| Type of vehicle |
Maximum allowable air loss |
| Straight truck, tractor or bus |
21 kPa (3 psi) per minute |
| Tractor and trailer |
28 kPa (4 psi) per minute |
| Tractor and two or more trailers |
41 kPa (6 psi) per minute |
