Operation and maintenance manual

Section 250-0070
SM 2165 Rev 1 11-03
3
metering notches become exposed to the inlet
pressure ports. This movement opens inlet ports 'P1'
and 'P2' to outlet ports 'B1' and 'B2' respectively.
As hydraulic pressure builds in the brake, oil flows
through the small orifice in the side of regulator spools
(16 & 14) and into the cavities below the spools. As
pressure rises in the brake it also rises in the cavities
below the spools forcing regulator spools (16 & 14)
upwards closing outlet ports 'B1' and 'B2'. Regulator
spools (16 & 14) are now balanced between the brake
pressure and the pressure of regulator spring (18)
generated by the operators force on pedal (1)
assembly. Regulator spools (16 & 14) have closed off
the inlet ports, outlet ports and the tank port and will
remain in this position as long as pedal (1) assembly is
not moved. If the operator further depresses pedal (1)
assembly, regulator spools (16 & 14) will move down
and build more pressure in the brake until it balances
the pedal force.
Normal Service Brake Release
Refer to Fig. 3. When the operator releases pedal (1)
assembly, regulator spools (16 & 14) will become
unbalanced and move upwards, opening outlet ports
'B1' and 'B2' to tank. At this point, oil in the 'B1' and
'B2' lines is released to tank through tank port 'T',
releasing the brakes.
Emergency Stop Brake Application/
Release
Refer to Fig. 4. Pressing/pushing of the emergency
control knob results in the de-energization of the brake
manifold valve solenoid. This allows full pressure to
enter the 'Px' port in the treadle valve simulating a full
and immediate depression of pedal (1) assembly, i.e.
pushing regulator spools (16 & 14) downwards and
thereby applying maximum braking action.
Refer to Fig. 5. Releasing the emergency control knob
will energize the brake manifold valve solenoid,
allowing the pressure in the 'Px' line to fall via the
return to tank port opened within the directional control
valve. Outlet ports 'B1' and 'B2' are opened to tank port
'T' allowing oil in the 'B1' and 'B2' lines to return to tank,
releasing the brakes.
REBUILD CRITERIA
Inspect the valve regularly for any signs of leakage or
damage. Check the actuator for excessive cam rock
and replace components if necessary.
The controller should be rebuilt if one or more of the
following conditions exist:
1. Any sign of external leakage.
Note: Check all hydraulic lines and fittings to ensure
Braking System - Treadle Valve
SM - 2770SM - 2769
Fig. 4 - Park/Emergency Brake Application Fig. 5 - Park/Emergency Brake Release
PX
P1
T1
P2
B1
B2
T2
6
7
TO FRONT
BRAKES
TO REAR
BRAKES
SUPPLY
FROM
BRAKE
MANIFOLD
SUPPLY
FROM
DIRECTIONAL
CONTROL
VALVE
SUPPLY
FROM
BRAKE
MANIFOL
D
PX
P1
T1
P2
B1
B2
T2
6
7
FROM FRONT
BRAKES
FROM
REAR
BRAKES
SUPPLY
FROM
BRAKE
MANIFOLD
SUPPLY
FROM
BRAKE
MANIFOLD
TO TANK VIA
DIRECTIONAL
CONTROL
VALVE