It is an essential component of a fire protection system, used to control the flow of water from a water main to a fire hose.
It is also known as a hydrant valve or a fireplug valve.
The valve shown is a flanged oblique angle type, commonly used in fire hose systems.
It is available from various suppliers of fire safety equipment.
The markings "DN50" and "PN16" indicate its size and pressure rating.