Operation and maintenance manual

Section 250-0050
Braking System - Brake Manifold Valve
2
SM 2158 7-02
T
P
A
3
2
B
P1
PY
ACC1
ACC2
PS1
PS2
PS3
P2
P
Return oil from the parking brake circuit enters the
brake manifold valve at port 'B'. The oil flows through
solenoid cartridge (2) and exits the brake manifold
valve at port 'T' to the hydraulic tank. With no pressure
in the parking brake circuit to hold the parking brake
off, the parking brake is applied.
Solenoid Cartridge - Energized
When the emergency brake switch is deactivated
(pulled out), the electrical signal between the switch
and solenoid coil (3) is closed, energizing solenoid
cartridge (2). Oil flows through solenoid cartridge (2)
and exits the brake manifold valve at port 'B' to the
parking brake circuit to release the parking brakes.
Return oil from the 'Px' port on the treadle valve flows
through the directional control valve and into the brake
manifold valve at port 'A'. The oil travels through
solenoid cartridge (2) and exits the brake manifold
valve at port 'T' to the hydraulic tank.
Pressure Switches
Accumulator pressure switches fitted to bottom of
brake accumulators send a signal to illuminate warning
lights in the dash panel when the pressure drops below
115 bar (1 668 lbf/in²).
Parking brake pressure switch (20) sends a signal to
illuminate the parking brake light in the dash panel
SM - 2750
when the pressure in the parking brake circuit drops
below 4.9 bar (71 lbf/in²).
REMOVAL
Numbers in parentheses refer to Fig. 1.
WARNINGS
Hydraulic fluid pressure will remain within the
system after engine shut down. Operate the
treadle valve continuously until the pressure
has dissipated before carrying out any work on
the braking system or serious injury could
result.
To prevent personal injury and property
damage, be sure wheel blocks are properly
secured and of adequate capacity to do the job
safely.
1. Position the vehicle in a level work area, apply the
parking brake, switch off the engine and turn steering
wheel in both directions several times to relieve any
pressure in the steering circuit.
2. Operate the treadle valve continuously to relieve
pressure in the braking system. Block all road wheels,
place the steering lock bar in the 'Locked' position and the
Fig. 2 - Emergency Brake Switch Activated - Solenoid Cartridge De-energized
2 - Brake Manifold Valve
TO DIRECTIONAL
CONTROL VALVE
FROM PARKING BRAKE
TO PORT 'P1' TREADLE VALVE
TO BRAKE ACCUMULATOR
TO BRAKE ACCUMULATOR
TO DIAGNOSTIC
PRESSURE CHECK POINT
FROM PRIORITY UNLOADER
VALVE/TO PILOT SUPPLY VALVE
(BODY HOIST SYSTEM)
TO PORT 'P2'
TREADLE VALVE
3 - Parking Brake Pressure Switch