The foot-operated valve is the means of applying air to operate the brakes. The amount of distance the treadle of the foot valve is depressed by the driver determines the amount of air pressure that will be applied, but the MAXIMUM APPLICATION WILL NOT EXCEED THE PRESSURE IN THE RESERVOIR. Releasing the foot valve treadle releases the brakes.

When the driver applies the brakes, depressing the treadle part way, the foot valve will automatically maintain the application air pressure, without the driver having to adjust the pressure of his foot on the treadle.

Releasing the treadle allows the application air to be exhausted through the exhaust ports to the atmosphere. Air treadles are spring loaded, producing a different ‘feel’ from hydraulic brake application.