Subaru 2002 Impreza Service Manual page 358

POWER STEERING SYSTEM
Power Assisted System (Power Steering)
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VANEPUMP
The vane pump consists of a rotor, a cam ring, and ten vanes.
When the rotor rotates, the vane movably fitted in each slot of the rotor is radially moved out by
centrifugal force and pressed against the inside wall of the cam ring. Since the inside of the cam
ring is oval-shaped, the fluid from the suction port is confined and pressurized in the chamber
formed between two adjacent vanes as the rotor rotates and is delivered through the discharge
port. The pressurized fluid circulates through the hydraulic circuit.
(1).
(1 ) Discharge
(2) Rotor
(3) Suction
NF0381
(4) Vane
(5) Cam ring
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FLOW CONTROL VALVE
The flow control valve regulates flow rate of fluid which otherwise would increase as pump speed
increases and deliver dangerously high pressure to the gearbox. It consists of orifices 1 and 2,
valve spool, return port and flow control spring. When a pressure difference occurs between the
front and rear of orifice 2 as a result of an increase in discharge rate, the valve spool moves against
the tension of the flow control spring in such a way that the oil flow rate is controlled by opening
and closing of the return port and orifice 2.
(1)
Pump speed
(2) Oil flow
(3) Idling
NF0382
(4)
When oil flow is not controlled
(5) Low and mid-range speeds
(6) High speeds
PS-14