You do not give enough information.

1. What are the liquids?
2. What are the viscosities?
3. What are the desired flow rates?
4. What type and max flow rate of the pump?
   
5. What is the temperature?
6. Are you planning on using the pump to mix these two liquids?

Mike

What I can tell is that temperature would be identical for both liquid. I was thinking using a mixing T downward the pump. I was wondering if there is a general formula that I can use to calculate the different diameter of the tubing. This way I'll be able to apply this approach for several liquid. I understand that viscosity, flow rate would be important parameter in order to calculate the needed diameter. The question is what are the other parameter i'll need to consider and which formula will connect them to the different diameter need to achieve the flow rate. Is such a formula exist? Is such approach have been use in industry? I guest solubility would also have to be take in account. regards, Alain

Use two separate positive displacement pumps driven by two separate motors speed controlled by VFDs (Variable Frequency Drives). This will allow you to control the volume/feed rate of each liquid. Be sure to use pumps suitable to the characteristics of each liquid.

IMO, trying to get a consistent mixture of the proper proportions using a T and some orifices, different sized tubing or even valves is going to be a major mess because of pressure, temperature and viscosity variations unless you have closed loop flow control for each liquid.

If the proportions are never going to change, you might get by using two positive displacement pumps driven at different fixed speeds off the same motor by varying the pulley, gear or sprocket ratio on one pump. If the mix ratio is 1:1 then just drive both pumps off the same shaft and use the same ratio. That should also work.

Along the same line but for a lower volume intermittent service, I saw an air driven reciprocating pump with two pumping chambers, one for each ingredient. This was used to mix two part expanding packing foam.

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