TM 5-3805-260-24
When the brake pedal is released, the air pressure
against the brake master cylinder is relieved (let out).
The master cylinder piston is retracted and hydraulic oil
pressure is let off of the caliper pistons. The residual
pressure valves (check valves) keep a 3 to 6 psi (20 to
40 kPa) back pressure on the pads to keep them against
the discs. The pistons and pads are not returned by
springs. They just release their grip on the disc. The
pads do not move away from the discs so no adjustment
is needed when the pads begin to wear because the
pads keep a little contact with the discs, the pads keep
the discs clean.
The air flow comes from three air tanks (3), (6) and
(7) filled by air compressor (1) through the air dryer (34)
(Models 613BSNS1 and 613BSS1). From the air tanks
the air flow is divided into four separate circuits: service
brake, emergency brake, parking brake and accessory
air circuits.
SERVICE BRAKE CIRCUIT
When the brake pedal is pushed, pressure air is sent
from brake control valve (28) to the tractor and scraper
air chamber and brake cylinders. The tractor and
scraper brakes are now engaged.
NOTE: Air from the control valve goes through double
check valve (27) before it goes to the air chamber and
brake cylinders.
EMERGENCY BRAKE CIRCUIT
When there is air pressure in all the air tanks, the
service (wheel) brakes can be used for emergency
brakes. Emergency brake control valve (30) is acti-vated
either manually or automatically. The valve is controlled
manually by a knob and automatically when air pressure
in the system is too low.
Air flows from wet tank (7) to emergency brake
control valve (30). The air holds the emergency brake
control valve in, which keeps the exhaust port closed. Air
then flows from the emergency brake control valve to
emergency pilot valve (23).
When there is pressure in the line from emergency
brake control valve (30) to emergency pilot valve (23) air
from reserve air tank (3) can not go through the
emergency pilot valve. When air pressure to the
emergency pilot valve is released through the emergency
brake control valve, the emergency pilot valve opens. Air
pressure from reserve air tank (3) now goes through
emergency pilot valve (23), double check valve (27) and
to the tractor and scraper brakes. The tractor and
scraper brakes are now engaged.
PARKING BRAKE CIRCUIT
Parking brake control valve (3 1) is activated either
manually or automatically. The valve is controlled
manually by a knob and automatically when air pressure
in the system is too low.
When there is no pressure in the air system, the knob
in parking brake control valve (31) is pulled out (parking
brake ON position). There is no air pressure in parking
brake chamber (8). The spring force in the parking
brake chamber keeps the brake activated.
After the engine is started and air pressure is at the
correct pressure for operation, the knob on the control
valve must be pushed in and held for a moment (parking
brake OFF position). Air pressure now goes from
parking brake control valve (31) to parking brake
chamber (8). The air pressure puts the springs of the
parking brake chamber in compression. The parking
brake is released.
ACCESSORY CIRCUITS
Part of the air pressure from wet air tank (7) goes to
window washer valve (18) and air pressure gauge (16).
The remainder of the accessory air circuits get air
pressure from dry air tank (6) and brake control valve
(28).
From the dry air tank, the flow of air is to seat
suspension valve (21).
From the brake control valve the flow of air is to horn
valve (25) and differential lock valve (26).
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