
AIR BRAKES AND AUXILIARY RETARDERS 449
actuators when the line pressure is released. This avoids
the delay in response associated with air from all the
actuators being evacuated simultaneously through long
runs of air line, before reaching the atmosphere via the
exhaust port of the control valve. Quick release valves
can therefore perform two functions in an air brake sys-
tem, since they can allow quicker release of the service
air brakes and quicker application of the secondary
spring brakes.
This type of valve is of simple construction, and
typically comprises a valve body with two ports con-
necting to a pair of brake actuators and a thir ...