Butterfly valve linkage calculatulation
Butterfly valve linkage calculatulation
(OP)
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.





RE: Butterfly valve linkage calculatulation
RE: Butterfly valve linkage calculatulation
Thanks for the response....
RE: Butterfly valve linkage calculatulation
RE: Butterfly valve linkage calculatulation
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.
Gr.
Terje
RE: Butterfly valve linkage calculatulation
RE: Butterfly valve linkage calculatulation
Root around on this site and see if you can find any help. Beck DOES NOT make Scotch Yoke actuators, but they have to do some actuation tricks with their actuators to make them more effective, so they might have something for you.
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Rotork makes Scotch Yoke electric actuators in their SM5000 series actuators. You might root around on their site and find something as well.
rmw
RE: Butterfly valve linkage calculatulation
RE: Butterfly valve linkage calculatulation
"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"
You've got to have a mechanism which will match (or approximate closely enough) the exponential (or quadratic or partial sine wave or whatever it is) flow curve. Then, like terje61 said, if densities and pressures change, it will shift the curve. Maybe that is splitting hairs too much and you aren't interested in that tight of control, just in following the general shape of the curve and being "in the neighborhood".
The first step is a good ol' exercise in Analytical Geometry, evaluating the flow curve to get a mathematical approximation. That is not too daunting a task for someone, unlike me, who remembers that stuff. Or some "CFD" program (Computational Fluid Dynamics) should be able to handle it. Then the next step is an exercise in Kinematics, designing a linkage arrangement to approximate your mathematic relationship. I don't remember if you can get there using a combination of circular arcs (lever arms). It is likely going to be a slotted plate/follower type arrangement, but the slot will need to be custom machined to generate the proper motion.
(Now just having said that, and having had another swig of Diet Pepsi this morning, it strikes me that surely someone already makes such a device. It would have to be adjusted/tuned to each installation, but we're not talking space travel here, just getting closer to the curve than the linear actuator.)
RE: Butterfly valve linkage calculatulation
Otherwise you can split the flow curve into segments (at least 3) for linear approximation and configure a stepped sequential linkage system for the linear actuator so that it acts at different points on the lever arm at different portions of its stroke, giving you different rates of disc opening for the fixed stroke speed.
(Light bulb!) You said you have a motorized actuator, do you mean an electric linear actuator ("electric cylinder") like a Duff-Norton or Allied? If so, and it's PLC-controlled, you can program the PLC to move it different incremental amounts in relation to the input signal and thereby accomplish the linear approximation.
Alternatively, although I've forgotten most of what I once knew about motor speed control and thus don't know how or if this could be economically accomplished, you could vary the speed of the motor in order to get the varying rate of disc opening.
The jist of it is that you're going to have to open the valve fairly slowly over the first 0 to 20-25-30%, then at a faster rate over the middle portion of the range, then slow again the last 20-25-30%. (This is for a 3 segment linear approximation, with a PLC you can fairly easily use more segments and get a closer approximation. Or if you can generate the mathematical equation approximating the flow curve and if your PLC has the processor for it, you can program the equation directly and avoid all the complications.)
RE: Butterfly valve linkage calculatulation
you can just put a Scotch yoke linkage on your existing actuator, if there if enough space