Hello guys i have problem. I delete half cylinder and use mirror. When i try get this effect: 
, i gets it:
, my vertices are connecting to center. This guy have selected only vertices. What im doing wrong?
Position the 3d curser to where you want the vertices to scale to (Shift+S) and set the pivot point to the 3d cursor
https://www.blender.org/manual/editors/3dview/transform/transform_control/pivot_point/index.html
More specifically, set the 3D cursor to the origin of the cylinder (Shit-S > Cursor to Selection) and then switch the pivot point to 3D cursor. You can change the pivot point from the 3D viewer menu bar, to the right of where you change between solid and wireframe, etc.