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Participant

Join Date: Mar 2013
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How to Tune a =% Valve with Linear Plug

03/12/2013 9:00 AM

Helo,

I got a question, How to tune a equal percentage control valve. I use my fluke to give 4-20mA signal. It is an Air-To-Close valve. The valve uses a camflex positioner were we use a equal percentage cam. The plug of the valve is linear.

I'm wondering how we can tune this correctly.

I know the Characteristic of Flow % and the Travel, How that works but is there a tabel of The travel with mA signal ?

Thanks

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#1

Re: How to tune a =% valve with linear plug

03/12/2013 9:19 AM

If it is a closed loop system, then there is not; because the flow is being measured (feedback) to generate a compensation which will be added to or subtracted from your mA control signal.

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#2

Re: How to Tune a =% Valve with Linear Plug

03/12/2013 10:04 AM

One cannot tune a loop without knowing what it is supposed to be doing. The valve is only the motive element in the loop. There must be other things, like a measuring device or two, and some idea of what is in the process. Without those? No hope.

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#3

Re: How to Tune a =% Valve with Linear Plug

03/12/2013 8:21 PM

exactly which positioner - model number?

Can you provide a link to the positioner's manual?

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Power-User

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#4

Re: How to Tune a =% Valve with Linear Plug

03/12/2013 11:59 PM

As far as I know, during calibration, the valves are calibrated 8in linear fashionand the positioner cam decides the flow characteristics.

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#5

Re: How to Tune a =% Valve with Linear Plug

03/13/2013 5:39 AM

You could always go to fuzzy logic.

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#6

Re: How to Tune a =% Valve with Linear Plug

03/13/2013 12:53 PM

How much resolution does the application require? How finite?

You must determine/know the ratio of valve travel to process flow in order to develop the table.

Flow rates at given temperatures and type of fluid being controlled is normally stated in the OEM valve specification sheet.

Obtain the spec sheet from the valve manufacturer, determine the required resolution for your application, measure the actual valve travel 0 -100%, cycle the valve manually 0-100% position, and measure the actual flow through the valve ( Example: Flow = 0 - 100 GPM) ,divided bythe desired mA signal resolution (Example: If 1mA => 6.25% of valve travel (100GPM/16mA) = 6.25 GPM per mA) apply the ratio and verify the flow to be linear throughout the entire valve travel. Example: 5 mA = 6.25GPM , 6mA = 12.5GPM, ETC.

Hope this helps.

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Participant

Join Date: Mar 2013
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#7

Re: How to Tune a =% Valve with Linear Plug

03/14/2013 2:56 AM

Thanks for t he reactions!

It is a control valve wich uses a DP flow measurement.

The positioner is a masoneilan type 4700 P.

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#8

Re: How to Tune a =% Valve with Linear Plug

03/14/2013 8:34 AM

May be you could use the graph and calibrate the positioner.

"X" axis is the % mA signal and "Y" axis is % travel.

Looks like 50% signal the valve should move around 13%,at 75% signal valve should be at around 37%

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