Valve - a device designed to open, close or regulate the flow when certain conditions occur (increase pressure in the vessel, change the direction of the current in the pipeline). The current can be a flow of liquid (water, blood, liquid metals, etc.), gas (air, nitrogen, carbon dioxide, etc.), electrons or other particles in a pipe, conductor, semiconductor, vacuum or other medium. The valve is one of the types of pipe fittings, which in English is collectively referred to as valves, but also includes valves, valves and butterfly valves. In contrast, the locking or regulating element of the valve moves parallel to the axis of the flow of the working medium.