ExperTune software for valves

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Thread Starter

parisa

hi
do you know any software for valve stiction?

i find ExperTune (plant triage) but i want other software

with best regards

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curt wuollet

Stiction is the tendency for a valve left in one position to want to stay in that position. Occasional dithering will combat this and the problems it causes. I'm not sure what software one would need for this.

Regards
cww

G

George Buckbee

Both PlantTriage and PID Loop Optimizer software have tools to identify and, more importantly, to quantify stiction.

Almost every valve will exhibit some small amount of stiction. It is important to be able to measure the amount of stiction to determine whether it is worthwhile to take corrective action.

The root cause of stiction can be one of many potential causes:

* Over-tightened packing
* Under-sized valve spring
* Low Air Supply
* Extremely viscous or sticky process fluids
* Damaged valve seats
* ...

When stiction is identified, we always recommend a physical inspection of the valve to determine the actual cause.

The dithering approach mentioned in another post may work to combat some of the root causes (sticky fluids), but will not work so well against others (tight packing). To see a recorded webinar, showing how to identify stiction and other valve issues, click on the link below:

http://www.expertune.com/r2p.asp?f=AList&t=Valve&l=ShowmePastWebinar.asp?name=Valve2010Mar16

-George Buckbee, P.E.

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parisa

> The dithering approach mentioned in another post may work to combat some of the root causes (sticky fluids), but will not work so well against others (tight packing). To see a recorded webinar, showing how to identify stiction and other valve issues, click on the link below:

http://www.expertune.com/r2p.asp?f=AList&t=Valve&l=ShowmePa stWebinar.asp?name=Valve2010Mar16 <

thanks dear George,

i researched about valve stiction and read some paper, but i want to know which methods are use in software. so i need the software detail.

i check this link, and fill my email address, but i cant find any data

G

George Buckbee

I would be happy to discuss with you. Please contact me via email :

george (dot) buckbee [at] expertune (dot) com

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Russ Kinner

I had a valve problem that looked like stiction but was a bit different. The valve was controlled by a bi-directional motor with electronics internal that converted a 4-20mA signal to raise and lower commands when needed. I found that the 4-20mA signal had to move about 2% before the valve moved - the ultimate reason had to do with the internal (and not adjustable) hystersis built in so that the valve didn't continuously hunt.

The result for the control was a "sawtooth" wave for the PV. Error would build up until the valve corrected (too far) and then the PV would start moving the other direction until the error in that direction was too much. This was on an oven which produced a material that was alternatively too dry and then to moist.

The solution in that case that I came up with was to intentionally cause the output to momentarily drop by 10% for 1 second - that caused the valve to start correcting and would continue to correct until the position error was at 0%. I did this roughly once every 90 seconds and the "sawtooth" waveform became much smaller.

This isn't "stiction" but it sure looked like it. Our customer was very happy and saved a boatload of  since they could reduce the over pack of the final product as it's package weight was more stable. I probably could still walk into the plant and get a few smiles from the old timers (and I'm on my 3rd employer after that project, probably 15 years ago).

Just because it looks like stiction it doesn't mean it is always the root cause.

Russ Kinner

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parisa

george,

it's your kind that help me,i sent you email.

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Ben Janvier

Russ, your technique to combat stiction is very good and will work where process dynamics are slow and are not affected by rapid changes in valve actuator movement. For instance, you can control precisely the temperature of an furnace by +/- 10% control action but you can't control flow through +/- 10%.

If you need to know and quantify small valve friction, this will be extremely difficult. Unfortunately, if your process is critical, a friction of 0.3% might be too much for your financial bottom line but if your signal is noisy the software will have a very hard time informing you about the sticky valve. In fact, you will need to wait a few month for the valve to degrade to 0.6%-1% friction for the software to flag anything. The reason is simple - these packages are allowed to miss things (no one knows) but will be turned off if they start giving false alarms.

What is the solution to valve stiction alarming: simplicity. Just buy a digital positioner and use an online performance software that will alarm you when the valve output differs from the valve position (there is not guessing game). True it is not sexy but it works (Maisoneilan and Fisher both carry this kind of package)

Ben Janvier, Senior Control Consultant

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