BC Transit – Air Brake Course

The Two-Way Check Valve
The two-way check valve will deliver application air either from the hand valve or
the foot valve to the trailer brakes. Which source delivered, depends on which source
has the higher pressure. If 20 psi were delivered from the hand valve, but only 10 psi
were delivered from the foot valve, the 20 psi from the hand valve would ultimately
be delivered to the trailer brakes. However, if 20 psi were sent from the foot valve,
and only 10 psi from the hand valve, the tractor and trailer would receive the same 20
psi brake application.
20 psi.
10 psi.
Left click for animation
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