Seems simple but I am looking for some software to help calculate the linkage geometry needed to linearize different size butterfly valves driven by a motorized actuator.  Actuator has slidewire feedback and would like to be close to linear as possible on the butterfly valve.  Valve is controlling air flow to burners on a furnace.  I basically only need a starting point.

On my furnace, a motorized actuator drives a butterfly air valve with a "connecting rod" or linkage.  The air flow through the butterfly valve is not directly proportional to how far open it is.  For example, when the valve is 10% open I may be getting 30% flow. when the valve is 20% open I may be getting 50% flow.  By connecting the linkage in the correct location on the arms of the valve and the actuator, I should be able to get a linear flow output through the valve that corresponds with the actuator position.  I was hoping to find software to assist in calculating this linkage "geometry".  Searched the internet with no luck so just looking for something that could give me a starting point.

I think that you would be really fortunate if you could get a linear relationship between your actuator and the valve flow.

1)
A butterfly valve has an inherent quick open characteristic. This explains the aggressive flow curve you describe in your second post. You need to contact your supplier and ask for this characteristic. But it will only be valid for standardised pressures and densities.

2)
Then you should calculate the installed characteristic by calculating the real flows at the operating pressures and medium density. Note that for each pressure situation you get a different curve. Since the differences are not that big you can probably group the curves and make a 'best fit' characteristic.

3)
The linkage has its own curve which you can easily establish by measuring the angles and length of the lever. Changing the length and angle will change this curve and you are looking for the opposite of the flow curve. This will require some trial and error work.

4)
Finally you will have something that approximately works. But when the pressures or densities change you will still get an ofset.

Now my question: is this worth it?
Probably not and that is why nobody is doing this exercise. Especially not if you have >100 valves on a plant.

My advise would be to just accept that the relation is not linear. It looks like you already did a flow test and as long as you know that 10% movement changes the flow with 30% you know how to control your process.

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