2-Way pump unit with 3-way mixing valve with 0-50% integ M2 MIX33

2-Way pump unit with 3-way mixing valve with 0-50% integ M2 MIX33


The unit for 1” (180 mm) circulating pumps consists of:



  • Connection.
  • 3-way mixing valve with adjustable by-pass. Through the by-pass (adjustable from the front part) it is possible to mix on the supply line a quantity of water coming back from the return line of the system, from 0 up to 50%.
  • Circulating pump with press-cable (for the models with it).
  • Flanged ball valve supplied with in-handle thermometer (coded red, range 0°C-120°C).



  • Flanged ball valve with non return valve 20 mbar (which can be excluded by rotating the handle by 45°) supplied with in-handle thermometer (coded blue; 0°C-120°C).
  • “T” Connection for mixing valve.
  • Connection.


Centre distance 125 mm. EPP insulation box (Measurements: 250x380x190 mm).

PN 10. Max Temperature 110°C.

External connections: 1” or 1”1/4 Female.



For power up to 35 kW (with Δt 20 K) and maximum flow 1500 l/h.

Kvs Value: 6,0.

Approximate data calculated with a 6 m nominal lifting power circulating pump.

For an accurate measuring or for higher flows, please refer to the curves shown in the technical section.


Available circulating pumps:


Wilo Star RS 25/6 (W6)

Grundfos UPSO 25-65 (G60)

Wilo Star RSG 25/8 (RSG8)*


Available circulating pumps for models with servomotor:


Wilo Star RS 25/6 (W6)

Grundfos UPSO 25-65 (G6)

Wilo Star RSG 25/8 (G8)*

We suggest you to install two isolating valves Art. 552 (see Correlated Articles) before the pump unit to allow an easy service or replacement of the components of the unit.


    The by-pass integrated into the 3-way mixing valve ensures a recyling inside

    the installation, even when the mixing valve is fully open. Through the by-pass,

    a fixed percent of the mixing (max. 50% of the total flow of the valve) can be set,

    in the case when the flow through the mixing valve is not sufficient.

    Therefore, in case of a bad working of the system causing an increase of the

    temperature of the installation, the recycling through the by-pass allows a decrease

in the temperature of the water in the undrefloor installation. This can be done mixing

the warm water of the return circuit with the hot water of the supply circuit, reducing

possible damages.


Approximate data for applications in low temperature heating systems


Approximate power

and flow of the installation


circulating pump


lifting power

Approximate surface of

the underfloor heating system

8K 17 kW - 1800 l/h

Wilo Star RS 25/6

3 mH2O

Up to 100 m2

8K 20 kW - 2200 l/h

Wilo Star RS G25/8

5 mH2O

Up to 200 m2

15K 31 kW - 1800 l/h

Wilo Star RS 25/6

3 mH2O

15K 38 kW - 2200 l/h

Wilo Star RSG 25/8

5 mH2O



Working principle


During the regular working process, with the mixer completely closed on the recycling for example, a part of the fluid is aspirated from the pump all along the by-pass line. This quantity of fluid (narrow blue arrow) represents 50% of the capacity of the mixer (red arrow). As a result, one has a very high delivered capacity and a reduced tempera



                                                         Adjusting the by-pas

                           Reference indicator                                     Reference indicator       


         The By-pass is fully open and it allows the               The By-pass is fully closed and there is no recycling.

         recycling of the 50% of the total flow.                        The screwdriver cut is in an orthogonal position (at 90°)

         The screwdriver cut is aligned along the reference          in comparison with the reference indicator.     





     Servomotor M21: 3 points servomotor for mixing valve. Bidirectional, reversible with fixed limit switches

      for an operating range of 90°. 

       230V, 2 min., torque: 5 Nm. IP42.

                                Several models available: see the section “Servomotors”. 



     CMP25-2 climatic controller: “touch screen” climatic controller with servomotor for mixing valve, 3 points. Bidirectional,

     reversible with fixed limit switches for an operating range of 90°. 230V, 2 min., torque: 10 Nm. IP42.



Versions available with reduced Kvs (using the special kits, see Correlated Articles). In the table below the resulting Kvs of the unit is shown, with the relevant maximum values of power and flowrate:



M2 MIX33:

Code 1”: 20355(R/L)-M33 - with circ. pump: 20355(R/L)-M33-(W6/G60/RSG8)

Code 1”1/4: 20455(R/L)-M33 - with circ. pump: 20455(R/L)-M33-(W6/G60/RSG8)


M2 MIX33 with built-in M21 servomotor:

Code 1”: 20355(R/L)-M33-M21 - with circ. pump: 20355(R/L)-M33-(W6/G6/G8)-M21

Code 1”1/4: 20455(R/L)-M33-M21 - with circ. pump: 20455(R/L)-M33-(W6/G6/G8)-M21


M2 MIX33 with built-in CMP25-2 climatic controller:

Code 1”: 20355(R/L)-M3-CMP - with circ. pump: 20355(R/L)-M33-(W6/G6/G8)-CMP

Code 1”1/4: 20455(R/L)-M3-CMP - with circ. pump: 20455(R/L)-M33-(W6/G6/G8)-CMP


“R” Codes: pump units with right supply. f.i. 20355R-M33; “L”Codes: pump units with left supply. f.i. 20355L-M33.

(*) The pump units with circulating pump Wilo RSG 25/8 (RSG8/G8) are not reversible. They are available only with right supply way.

  • Model: M2 MIX33