Service Manual
HR15/17N HYBRID DC
English 07/16
48
5.8
Valve Block Assembly
The valve block assembly is made up of two components, the Drive Control Valve (DCV) and the Flow
Control valve blocks. Together these form the distribution hub of the hydraulic system. The table below
describes the main functions. Refer to Hydraulic schematics D81900 (Hybrid) and D81500 (DC Electric).
5.9
Diff Lock
The diff-lock divides/combines the flow to both rear wheels equally when in operation. Bypass restrictors
are fitted to help with cornering manoeuvres. Pressure is supplied from the Drive Control Valve to the
wheel motors.
When Tortoise or Off-road speed is selected, the diff-lock is engaged and both rear wheels are driven. As
with all diff-lock systems, power consumption is increased with the diff-lock engaged, steering whilst diff-
lock is engaged further increases power consumption.
Diff-lock is not engaged when Hare speed is selected. In this mode ports A/B of the rear wheels are no
longer supplied via the divider/combiner valve and flow is free to go to either of the two rear wheels.
5.10 Brake Release
The rear brakes are released using the Brake Release Valve (BRV) in the DCV which is energised when
driving. The rear brakes are released only when driving.
5.11 Steering
Steer Valve
When steer is activated, steer flow is supplied from the DCV via the steer enable valve. This controls the
flow to the steer valve and connects the load sense signal to the pump to allow simultaneous operation
of drive and steer. Steer valve controls the direction of steer. Pressure Reduction Valves fitted to the main
DCV limit the maximum pressure on the steer line to 160 Bar (2321 psi). This will disable steer when the
cylinder reaches the end of stroke.
Function
Description
Drive
Controls drive forward and backward. Provides proportional speed control for
both directions.
Brake Release
Supplies 30 bar (435 psi) of pressure to the rear brake release valves.
Steer
Enables 2 L/min flow to the steer valve and enables pressure compensation.
Elevated Drive
Maximum flow is limited for elevated drive. Full flow is enabled for high speed
drive.
Boom enable
Enables 25 L/min maximum flow to booms valve.
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