I have a basic valve which I want it to turn when player is using "e" (use key) and stop rotating when player releases use key. Momentary_rot_button supposed to do just that what I am looking for but I have encountered a problem, the hold "e" (use key) is not really working, it acts as a press.
So did I miss something or this entity is broken in portal 2 (as it works in hl2, css and so on).

I'd love to help but I haven't tried it myself. It gets me thinking, I can't come up with any official Portal 2 map that let's the player hold in the E button. In that case I would recommend to decompile their map and check it out, but I can't. Sorry.

What I come to think of is to manually add a line to the entity. Take the move_rope entity as an example. No Portal 2 map, that I know of, has rope that sways with the wind. They are all static. So I got the recommendation to add my own line to the entity. The command exists in other Source games but it doesn't in Portal 2. My point is that the entity isn't exactly the same in Half-Life 2 or Counter-Strike Source as it is in Portal 2. I'd try to compare them carefully and see if there's a command line missing in the Portal 2 entity.