Single shunt with 3-way valve in return pipe

A single shunt mixing loop with 3-way valve in return is used when variable flow is desired on the secondary side, but not variable temperature.

Function:

• Secondary side:
  The load will normally be an exchanger, where the temperature out of the exchanger is the setpoint.
  The flow decreases when the valve is closing.
  The valve can be placed either in the flow pipe or in the return pipe.
  The pressure lost in the bypass has to be close to the same as the pressure lost in the system.
• Primary side:
  The flow is constant, but the differential temperature will change when the valve is adjusting.

Interaction with speed-controlled pumps:

• Primary side:
  A pressure-controlled pump will not react when the valve is adjusting, but it is possible to employ speed control on the pump based on temperature, constant return temperature or constant differential temperature.

Grundfos pumps are typically a part of heating systems where a single shunt mixing loop is used when variable flow is desired on the secondary side.