Every time that steam is expanded in a pressure reducing valve, it gets superheated because of the experienced evolution (isoentalpic expansion).
When low pressure steam is used as a heating media, saturated or slightly superheated steam should be prefered.   The easiest way to saturate steam is to inject cold water, which lowers the steam temperature by evaporating and brings it close to saturation.  There are several equipment which can do this task, differing mainly in the way in which they atomize the water.

Venturi desuperheater is a self atomizing type device.  Cooling water is introduced into the central nozzle by flow of steam at high velocity.  When leaving the nozzle, the fog enters the main flow at the venturi throat without contacting the side walls, getting effective desuperheating with minimum erosion, close approach to saturation temperature and moderate turn down ration.

Venturi assisted desuperheater: Uses high pressure steam to atomize the cooling water. It has turndown ratios of 50 to 1 and very good approach to saturation temperature.

Mechanical desuperheater is the  simplest desuperheater.  It uses high pressure water in a special nozzle to obtain the atomization.  It is used for low approach and turn down ratios.

Standard size: from DN 50 (2") to DN 600 (24")

Materials: 
CS body and difuser