BC Transit – Air Brake Course

The Foot Valve
Two typical foot valves are pictured here. The uppermost one is used
primarily in buses. The lower example is suspended from the firewall and is
used mostly in trucking applications. They operate in precisely the same
way, being spring loaded and self-balancing.
We need to know...
•The foot valve is considered to be the most important valve in the system,
because without it, we could not control brake application pressure.
•It is a self-balancing device, meaning that even if a small leak occurred in the
system during a brake application, the foot valve would regulate the application
air such that the brakes would remain applied.
•The foot valve is spring loaded, so the operator feels only the spring pressure,
not the pressure of the brake application, as in a hydraulic brake system.
•Maximum brake application pressure available at any time is only that which
is present in the system’s reservoirs. Application pressure cannot exceed
reservoir pressure.
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