10 - 3
Section E Hydraulics
9803/8550
Section E
Descriptions
10 - 3
Issue 4
2 Loader Valve
2X Pressure Test Point
2Y Pressure Test Point
3 Check Valve (5 bar)
4 Excavator Valve
8 Drive Control Joystick
8a Joystick Control Spool
8b Joystick Control Spool
8c Joystick Control Spool
8d Joystick Control Spool
8e Shuttle Valves
9 Pressure Reducing Solenoid Valve
11 Filter By-pass Valve
Key
C Cooler
F1 Filter
P1 Main Pump
P2 Main Pump
P3 Auxiliary Gear Pump
Pa Charge Valve
Pb Pressure Relief Valve
Pc Pressure Relief Valve
Pd Pressure Relief Valve
Pe Pressure Relief Valve
M1 Left Hand Drive Motor
M2 Right Hand Drive Motor
S1 Suction Strainer
T Tank
Transmission Operation - Neutral
With the engine running but no drive selected, oil
from pump P3 is fed through the loader valve 2,
excavator valve 4 and filter F1 to main pumps P1
and P2. A small amount of oil flows through the
charge valve Pa, enters the pump casing and is
returned via line z to tank T.
Oil is also fed from pump P3 to the transmission
servo joystick 8 but, because the joystick is not
operated, the oil is blocked by the spools 8a, 8b,
8c and 8d and therefore no servo pressure is
applied to operate the swash plates of pumps P1
and P2.
As the pump swash plates are spring loaded to the
neutral position there is no delivery from either
pump and the machine remains stationary.
The motor brakes x and y are released whenever
the engine is running by oil fed through the
pressure reducing valve 9. However the machine is
prevented from moving by oil locked up in the
pump/motor circuit.
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