Valve Functions and Basic Parts Summary
There are four basic types of flow control elements employed in valve design.
1. Move a disc, or plug into or against an orifice (for example, globe or needle type valve).
2. Slide a flat, cylindrical, or spherical surface across an orifice (for example, gate and plug valves).
3. Rotate a disc or ellipse about a shaft extending across the diameter of an orifice (for example, a butterfly or ball valve).
4. Move a flexible material into the flow passage (for example, diaphragm and pinch valves).
Valve stem leakage is usually controlled by properly compressing the packing around the valve stem.
