BC Transit – Air Brake Course

Primary Air Loss and Park Brake Function
In a primary air loss situation, the subsequent events are similar to a secondary air loss.
The two-way check valve moves toward the low pressure side (primary reservoir.) The
one-way check valve at the inlet to the secondary reservoir closes. The park brakes
remain released, held so by secondary air only. Now, however, we’ve lost the primary
brakes so stopping the vehicle becomes much more difficult. The operator would need to
manually apply the park brake, which could result in rear wheel lock-up. This is one of
the events we were trying to prevent by adding dual air.
Left click for animation
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