power steering problems

Ok I took the 2 bolts out and removed the slide valve on top. I see a exposed screw with a spring around it. Is this what I am adjusting to center the steering. Just by sliding it from side to side? It looks like you could adjust the screw for something. The slide on the top fitting had rubber pieces in the holes. I cleaned it. If I can find it I have another top piece somewhere. I may put it on just for grins to see what it does.