Demand For Assistance (Valve Misaligned)
When the steering wheel and input shaft is turned, steering resistance transmitted to the worm causes the torsion bar to be twisted and the valve ports to be misaligned for a right or left turn. The misalignment of the valve ports directs all fluid pressure to one side of the piston only and allows displaced fluid on the other side. See Fig 1 . When demanding maximum assistance, any excessive fluid output from the pump due to high pump speed, will circulate through the regulator valve located in the pump unit. This causes the temperature of the fluid and the pump to rise rapidly. To avoid excessive fluid temperatures which could damage the oil seals, the steering must not be held on full lock for more that 30 seconds in one minute. Only when the steering wheel and the demand for assistance is released, will the torsion bar return the valve to neutral, allowing the fluid to circulate through the reservoir where it is cooled. In the event of mechanical failure of the torsion bar, a coarse splined connection between the input shaft and worm ensures steering control is maintained sufficiently to allow the vehicle to be recovered.