There are 4 basic types of menses command elements employed inwards valve design.
1. Move a disc, or plug into or against an orifice (for example, basis or needle type valve).
2. Slide a flat, cylindrical, or spherical surface across an orifice (for example, gate as well as plug valves).
3. Rotate a disc or ellipse virtually a shaft extending across the diameter of an orifice (for example, a butterfly or ball valve).
4. Move a flexible fabric into the menses passage (for example, diaphragm as well as pinch valves).
Sumber http://mechanicalgalaxy.blogspot.com/