Most walking feet have a "fork" that hooks around the needle tightening screw. The only walking foot I have seen like this, with a bar that goes on top of the screw instead of around it, was for a Janome. I think all of the generic feet I have seen have the fork, as does my Bernina walking foot.
Someone mentioned there is a way to adjust the spring in a darning foot, but I don't know how to do it. If you cannot manually move the foot up and down on the spring, it seems to me the spring must be broken. I can push mine up, and it will "spring" back to its original position.