"The brass-colored device in the upper right hand corner of the photograph is called a 'ball drip' valve. A ball drip is one type of automatic drain valve that may be attached to the supply pipe for the fire department connection on a waterbased fire suppression system where a fire department connection is required. This might include sprinklers, standpipes, high-pressure mist systems, water-spray systems, or any other system where it is considered desirable that the fire department has the opportunity to supplement the system's pressure and volume."
Coffee Break Training - Fire Protection Series No. FP-2009-17
United States Fire Administration: http://www.usfa.fema.gov/