Here's how a hydraulic power steering rack works:


Here is the steering rack removed from the car. It forms part of a hydraulic circuit that aids the movement of the steering rack when the wheel is turned.

Inside the pinion gear housing is the rotary valve:


This is the spool which collects the fluid into different channels and redirects it according to which side you are turning:

Inside the rotary valve housing are the holes for the hydraulic lines that correspond to different channels on the spool.

The rotary valve consists of a small torsion bar that twists a few degrees. This twisting action is what redirects fluids through the spool to either the right or left side of the rack piston:



Enjoy!

 

Wow. Glad I just paid for a reman when mine started leaking . Nice piece!