Steering and parking at low engine speed: The pressure produced by the pump is slightly reduced over the restrictor at the pump outlet. The reduced pressure is led to the spring loaded side of the control valve, at which time there is a minor pressure difference between the two sides of the valve. Due to the low pump speed, however, this pressure difference is not enough to actuate the valve.
Steering at high engine speed (pump in flow control mode): The flow of power steering fluid inside the pump increases with increasing engine rpm and owing to the restrictor 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 constant rate, regardless of engine /pump rpm.
Steering wheel turned to full lock: Pump speed in this case is often low. When the steering wheel is turned to full lock, the control valve of the steering gear closes. The flow of fluid from the pump will then be zero. The resulting high pressure is directed via the connection passage to the spring loaded side of the control valve. The pressure opens the overflow valve and allows the fluid to pass to the inlet side of the pump. The pressure difference across the control valve forces it to move against the spring and thus open the port for recirculation of the full delivery flow from the pump. The predetermined maximum pressure is maintained as long as the control valve remains closed
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