A valve is a component used to regulate or shut off the flow of liquids or gases. In this sense, it is a type of fitting and, therefore, a shut-off device. It is important to note, that not all types of fittings are classified as valves.
For example, butterfly valves or ball valves do not belong to this category. The actual valves consist of closure parts that move along the medium's flow direction. The flow interruption occurs when this closing part is pressed into the valve seat. In other cases, sealing is achieved in various shut-off devices using a closure coated with rubber or a diaphragm.