Research And Insight

Single shunt with 3-way valve in flow pipe

A single shunt mixing loop is used when variable flow or variable temperature or both are desired on the secondary side.


  • Secondary side: 
    The load will normally be a heat surface or a radiator system, where there is a demand for a variable temperature. Due to a reduction in the flow temperature, the flow in the secondary side will normally be higher. The flow can be constant or variable, depending on the system. The valve can be placed either in the flow pipe or in the return pipe.
  • Primary side:
    The flow decreases when the valve is closing. If an uncontrolled pump is installed on the primary side, the differential pressure in the connection point will increase when the flow is decreasing.

Interaction with speed-controlled pumps:

  • Secondary side:
    Due to the higher flow in the secondary side, a speed-controlled pump will have the authority in the secondary system.
  • Primary side:
    The pump will reduce the speed when the valve is closing. Normally proportional pressure control is recommended in systems where the pressure loss is split between the pipe system and the control valves.

Grundfos pumps are typically a part of heating systems where a single shunt mixing loop is used to control flow and temperature.

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