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Testing air-pressure build-up time
 

The air compressor must be capable of meeting the demand of the air brake system and restoring pressure to the normal range quickly. This is confirmed by testing whether air pressure rises to a specified level within a specified time.

To test the air-pressure build-up time, reduce the system pressure to below 552 kPa (80 psi). If the vehicle has a trailer attached, ensure the trailer supply valve is closed (pulled out). With the engine idling between 600 and 900 rpm, observe the time required for the air pressure to rise from 587 kPa (85 psi) to 690 kPa (100 psi).

If the time required to build up air pressure exceeds two minutes, the air brake system is defective.

Step-by-step procedure

  1. Lower air brake system pressure to below 552 kPa (80 psi).
  2. Run the engine at 600 to 900 rpm.
  3. Observe the primary and secondary air-tank pressure gauges.
  4. Note the time when pressure reaches the start value of 587 kPa (85 psi).
  5. Note the time when pressure reaches the end value of 690 kPa (100 psi).

Pass

Vehicle passes the test if pressure build-up time is equal to or less than two minutes.

Fail

Vehicle fails the test if pressure build-up time is greater than two minutes.

Important: The Ontario Highway Traffic Act and regulations prohibit operation of a vehicle that fails to build air pressure within the prescribed time.