Here's how a hydraulic steering rack works to turn the wheels on your car.
Hydraulic steering has been used for decades to provide assist to drivers turning the wheels of especially heavy vehicles.
Fluid is pressurized by a hydraulic pump and is sent to the rotary valve via the high pressure hose.
The rotary valve has a small torsion bar, which connects its input shaft (from the steering column) to the output shaft (the pinion gear). The torsion bar twists slightly, opening up a small passageway for fluid to escape and be lead out to the piston.
Depending on the direction, the fluid is pushed into the opposite side of the cylinder housing, pushing the piston. The piston is connected to the rack, which connects the tie rods and hence the wheels at the steering knuckle.
Once there is no more torque on the steering wheel, the torsion bar resumes its rest position, and fluid is fed back to the reservoir to be recycled again at the pump.
Mechanically, the pinion links the steering wheel to the rack, to provide a manual method of steering as a fail safe.
Hydraulic power steering setups are rather inefficent, which of recently has given way to the trend of electric power steering, where an