Terex TR60 Maintenance Manual page 446

Braking System - Directional Control Valve
Section 250-0090
B A
9
b
T
P
BRAKE
MANIFOLD
VALVE
Fig. 2 - Directional Control Valve - Energized
OPERATION
Numbers in parentheses refer to Fig. 1.
Refer to Fig. 2. When the engine is running,
transmission control pressure enters the directional
control valve at port 'a'. Oil pressure forces spool (3)
against spring (7) pressure, at port 'b' side of valve
body (1), internally linking port 'P' to port 'B' in sub
plate (13). This results in an open circuit between the
brake manifold valve and port 'Px' in the treadle
valve.
Depending on the condition of the park/emergency
brake switch, oil flows through the directional control
valve to energise or exhaust the 'Px' port on the
treadle valve as follows:
Park/emergency brake switch activated (pushed in) -
Oil flows through the directional control valve to the
'Px' port in the treadle valve.
Park/emergency brake switch deactivated (pulled
out) - Return oil from the 'Px' port in the treadle valve
flows through the directional control valve, through
manifold brake valve solenoid to the steering and
brake control tank.
Refer to Fig. 3. When the engine is shutdown, the
park/emergency brake switch is automatically applied
and transmission control pressure is relieved from
port 'a'. Spring (7) pressure, at port 'b' side of valve
body (1), forces spool (3) back, internally linking port
'B' to port 'T'. This results in an open circuit between
the brake manifold valve and port 'Px' in the treadle
valve.
2
TO 'PX' PORT
TREADLE VALVE
a
SM - 1510
9
B
b
Fig. 3 - Directional Control Valve - De-energized
A controlled bleed down of the applied service brakes
to the steering and brake control tank occurs through
the directional control valve. This controlled bleed
down permits a synchronised service brake release/
mechanical park brake application. Refer to Section
250-0000, BRAKING SYSTEM SCHEMATIC.
Note: On engine shutdown, brake accumulator
pressure is dead headed at ports 'P' and 'A' in the
directional control valve.
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 and switch off the engine.
2. Operate the treadle valve continuously to
discharge the brake accumulators. Block all road
wheels.
FROM 'PX' PORT
TREADLE VALVE
B A
a
T
P
BRAKE
MANIFOLD
VALVE
SM - 1511
B
SM 1226 2-98