Why is the link curved? What determines the curvature?

Link is curved so that when the position of the radius rod is changed (engine is hooked up or down or whatever), the centerline of the valve's motion is not changed. Were the link straight, you'd be dealing with angularity effects, and the valve events wouldn't occur at the proper time. The length of the radius rod is the radius of the link. -Chris

The link is curved because a straight one will make the valve move when you change direction and the valve gear stands whith the exentric rod in mid position. When curved it doesnt move at all - thats one of the first checks you take when checking the exentric rods length and the angles of the exeentric krank at the time you are setting the valves. The radius of the curve is set by the distanse between the links rocking axle and the valves crosshead. Dont forget the linkrod to the pistons crosshead that gives led and lap. Ragnar, who doesnt use anything but Walshaerts valve gear.

Please correct me if I am wrong, but my recollection is that the curvature of the link is a function of the length of the radius rod from its point of attachment to the combination lever to the pin where it engages the link. The curvature is necessary to maintain the same effective center point in valve travel as the radius rod position gets moved up or down by the reverse gear and lifting link. It is sure a lot easier to visualize the operation of steam locomotive valve gear with one of those old classroom "steam instructor" models, where you can move the linkages and see the result.

Oops, I grabbed a snack and left the page up and I see a couple of you nailed this already. Nice work guys!