Variable Spray Desuperheaters (VSD)

Variable Spray Desuperheaters (VSD) are recommended under low load conditions where the load is reduced and the spray nozzle area is also reduced.

The VSD provides more economical control of steam temperature by introducing cooling water into the steam flow through a nozzle of advanced design.

The design of the Desuperheater eliminates the need for a separate water Control Valve, which allows maximum water pressure at the nozzle.


  • Custom design
  • Precise control
  • High rangeability
  • Easy installation
  • Low maintenance


The VSD consists of a piston ring, stem, nozzle tube, nozzle head, seat ring, and plug. The nozzle tube assembly fits into the bore of the mounting flange and is locked in place by a retaining ring. As a result, the coolant inlet connection can be located in any direction in relation to the nozzle spray discharge.

Working Principle

  • The VSD utilises constant water pressure to create a fine conical spray into the steam main
  • Water at a pressure 4 to 5 bar above superheated steam enters the Desuperheater and flows down the angle style body to the nozzle area
  • Nozzle design allows the water spray jet to disperse into fine particles and distribute evenly across the flow path of the steam
  • Contoured equal percentage plug design creates a variable area around the nozzle


  • VSD’s are small enough to mount through a DN 100 flange in the steam main, having a minimum of 6 meters of straight pipe work downstream of the nozzle
  • Its unique 45° mounting arrangement minimises the water fall out rate and provides very low steam pressure drop across the Desuperheater, which are common problems with radial flow and co-axial Desuperheaters respectively

Desuperheater Installation Example

VSD Variable Spray Desuperheater Standard Installation


  • Steam Turbine Bypass to Condenser
  • Steam Turbine Exhaust to Process Heating
  • Auxiliary Steam
  • Boiler Superheater Attemperation
  • Boiler Re-heater Attemperation