This is my Node Setup. I have a Subsurf Modifier that's set to adaptive with a dicing scale of 1 pixel and the displacement settings on "True". Despite all of that there's no displacement in both the rendered viewport and rendered image.
No need for a bump node there, I would rather substitute it with a "math -> multiply" node, with which you can change the displacement height. In fact, what you are doing is taking a greyscale image, making a normal map out of it and plugging it into the displacement slot, which needs a greyscale image. But now you have wrong shades of grey because of that.
You also need correct render settings: In the render tab, in the render pane, you need to change the feature set to "experimental" and in the material tab, in the settings pane, the displacement to "both". (And obviously you need your mesh to be unwrapped properly.)