MEGA Corp. MSC-OPS-1 - Manual (Page 25)

MSC/MST-OPS-1
31 Dec 2013
SECTION 2
System Description
2-16
PARKING /EMERGENCY BRAKE SOLENOID
A 24 VDC electrical solenoid that
opens or closes to control the
parking or emergency brake
function. The solenoid valve
responds to electrical signals as
commanded by the parking or
emergency brake in the tractor
cab. The solenoid valve will open to
bleed off parking/emergency
brake release pressure from the
brake pods. This release of air pressure will cause the
parking/emergency brakes to be applied.
PARKING BRAKE PRESSURE SWITCH
A 24 VDC pressure switch used
to illuminate the parking brake
warning light in the tractor cab.
The sensor will turn on the
parking brake warning light
when parking brake release
pressure drops below allowable
limits.
SERVICE BRAKE RELAY VALVE
A pneumatic relay that
controls and routes air
tank activation pressure
to both brake pods. The
relay controls air
pressure applied to the
brake pods as
commanded by a
pneumatic signal
generated by activating the service brake pedal
located in the tractor cab.
BRAKE PODS
A pneumatic cylinder designed to extend or retract
and apply service, parking or emergency brakes. The
pods are mounted to the MSC/MST rear bogie and
are connected to the wheel group brake activation
lever. The pod contains a coil spring and responds to
pressure received from the brake relay valve as
commanded by service brake pedal. The pod will also
apply parking or emergency brakes when one side of
the cylinder is depressurized when commanded by
the activation of the parking or emergency brakes.
Lose of pneumatic pressure allows the brake pod coil
spring to extend the rod end.
THEORY OF OPERATION
Parking Brake
The parking brake is applied by activating the
parking brake switch in the tractor cab. Once the
switch is moved to the park position an electrical
signal is sent to the parking brake solenoid valve
mounted on the rear bogie pneumatic manifold.
The sent signal will open the solenoid valve allowing
pneumatic pressure to decrease from one side of the
brake pod. The brake pod coil spring can now
overcome air pressure and extend the brake pod rod
end attached to the wheel group brake lever and
apply the brakes. Once parking brake pneumatic
pressure drops below allowable limits, the parking
brake pressure switch mounted on the pneumatic
manifold will close and illuminate the parking brake
warning light in the cab of the tractor.
The parking brake is released by activating the
parking brake switch. Once the switch is moved an
electric signal is sent to close the parking brake
solenoid valve. The valve closing will allow