Ransomes G - PLEX WD series Service Course Manual Download

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HYDRAULICS

SECTION 8B. STEERING AND LIFT CIRCUIT

8B-5

SPECIFICATIONS

Pump:

Charge pump of the Sundstrand Series 15 Transmission pump. 5.4 cc/rev 18.3 litres/
min at 3400rpm engine speed.

Steering valve:

Eaton five port valve.

Steering Relief Valve: Implement valve fitted to the Sundstrand Series 15 Transmission pump.

69 bar (1000psi)

Speed restrictors:

1.27mm (0.050”) in both lines to centre unit ram, one being located in the Sequence
valve.

CIRCUIT DESCRIPTION

NOTE:

All hydraulic pump outputs and pressures are given with the engine at maximum rpm and with the oil at

working temperature.

Oil is drawn into the charge pump from the hydraulic reservoir (

Shell Tellus 46

grade or equivalent) via the 25

micron suction filter. The oil is displaced by the (5.4cc) gerotor pump at a rate of

18.3

litres/min

, at an engine

speed of

3400 rpm.

From the pump the oil flows to the “

P”

port of the Eaton steering valve. When turning the steering wheel oil is

fed from the valve to the double acting ram at the rear of the machine. Oil displaced from the other side of the ram
returns to the hydraulic reservoir via port

“T”

of the steering valve. The maximum pressure available for steering

1000psi.

An implement valve located in the Transmission pump controls this pressure.

If the steering wheel is not being turned then the oil flows out of steering valve from the

“PB”

port to the

“P”

port of the lift valve. If the lift levers are not being used oil flows past the spools out of the

“T”

port of the lift

valve to the oil cooler and then on to the hydraulic reservoir.

When raising units the rear of the foot pedal is pressed which energises the lift valve solenoid thus moving the
spools to feed oil out of the

“A”

port opening the check valve as it does so. The oil then goes to the front rams,

which extend and raise the units. The flow combiner/divider ensures that the front rams lift at equal speed by
controlling the rate that oil is displaced from the rams. The oil also goes to the centre ram but as the sequence
valve is closed it prevents oil within the ram from being displaced so the unit cannot lift.
After a short delay the sequence valve opens allowing the centre unit to raise. The oil flow to the centre unit ram
and from the sequence valve is restricted to slow the raise speed. Oil displaced by the rams goes though valve
port “B”

before returning to the oil cooler and reservoir.

If the Operator continues to press the foot pedal the pressure would build until the

1000psi

implement relief

blows. When the pedal is released the oil is trapped between the rams and the check valve preventing the units
from dropping.

Pressing the front of the foot pedal energises the lower solenoid on the lift valve moving the spool and allowing
oil to flow out of port

“B”.

At the same time the check valve in port “A” is lifted off its seat via a pilot line. Oil

flows to the front rams via the flow combiner/divider ensuring the units lower at the same rate. Oil also flows to
the sequence valve but this is closed initially.
After a short delay the sequence valve opens and the centre unit lowers, it’s speed controlled by the restriction
created by the orifice in the line to the valve and another fitted in the line from the ram. Oil displaced from the
rams has to pass through the open check valve in port “A” before returning to the oil cooler and reservoir.

Flotation of the units whilst cutting is not restricted in any way by the rams as they locate in slots in the unit arms
allowing full articulation.

IMPORTANT NOTE: When turning the steering wheel on a continuous full lock the implement valve will blow
and this will prevent the lift circuit from working. This is a characteristic of the circuit that should not present a
problem when the machine is used as intended.