Q:

How do you perform an air brake test?

A:

Quick Answer

Perform an air brake test by checking the emergency brake, cut-in and cut-out limitations, static air levels, applied air levels and low-air alarms. You should also inspect the braking system for any obvious damage and check to ensure that the push rod moves between 1.5 and 2 inches when engaged.

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Full Answer

Test the emergency brake by applying it at a speed of approximately 5 miles per hour and verifying that the vehicle stops within 20 feet. Release the emergency brake, and park the vehicle. Press down on the pedal until the air pressure drops below 70 to around 40 psi. At this level, the low pressure alarm should sound and the emergency brake should activate.

Release the pedal and watch to see how the compressor refills the tanks. The cut-in limit should ensure that the primary tank gets to about 85 psi and stops filling until the secondary tank reaches the same level. When both tanks reach 125 psi or more, the cut-out limit should stop the compressor from filling them any further. Turn off the unit and watch the pressure in the lines to make sure that it remains within 1 psi of its last reported position. Press down on the brake pedal for one minute. The air pressure should not drop by more than 4 psi.

Perform a visual check of the system and have a friend depress the brake pedal while you measure the movement of the push rod with a yard stick to ensure it falls within the proper 1.5- to 2-inch range.

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