Understanding industrial control valve design and operation is very important if you work as a process engineer, a plant maintenance person, or if you design process control loops. Control valves are used extensively in power plants, pulp and paper mills, chemical manufacturing, petro-chemical processing, mining facilities, HVAC and steam distribution systems.
There are many types, manufacturers, body styles, and specialized features, but the they all share some basics operating principles. The video below explains components, operation, and fundamentals of how control valves operate.