900 SE Convertible L4-1985cc 2.0L DOHC Turbo EFI (1998)
REGULATION AT LOW RPM
The pressure raised by the pump (shaded portion in illustration) is reduced slightly by the restriction in the pump outlet.
The reduced pressure is also communicated to the spring loaded side of the control valve, giving rise to a slight pressure difference between the two
sides of the valve. Owing to the low speed of the pump, however, the difference in pressure is insufficient to overcome the force of the spring and
actuate the valve.
REGULATION AT HIGH RPM (PUMP IN FLOW CONTROL MODE)
The flow of hydraulic fluid inside the pump increases with increasing rpm and owing to the restriction in the pump outlet the flow velocity also
increases. This reduces the pressure in the connecting passage, with the result that the pressure on the spring loaded side of the control valve will be
lower than that acting on the outlet side of the valve. The valve therefore overcomes the force of the spring, opening a port to the suction side of the
pump and allowing a certain amount of internal recirculation of the fluid to take place so that the flow from the pump is maintained at a constant rate,
regardless of engine/pump rpm.
