Breakaway torque for Trunnion Ball valve, different seat 2

[Xun2006]

Good morning dear all,

I am new to valve industry, our sales threw a question to me regarding if they are changing seat material from, how much torque will added to actuate the valve.
1.) NPS 16, class 600, Trunnion ball valve, seat material changing from Nylon to Peek, what might be the approximate breakaway torque increase? (I assume as 15%)
2.) What will be the approximate breakaway torque increase changing from resilient seat to metal seat for trunnion? What about floaters?
Can anyone give some lights on it? Any help will be greatly appreciate

Xun

 

[bao2ye]

The torque definitely will increase. How much the torque is depends on your valve structure design, size, service condition.
You can calculate or test the torque.

Regards

Bao

 

[gerhardl]

What size does the valve have? Actuation type?

Following link on other properties than torque could be interesting for you

http://www.curbellplastics.com/technical-resources/pdf/plastic-material-selection.pdf

The link shows the materials to be fairly close in properties, and perhaps not too far from eachother in loosening torque.

As a reminder: Necessary torque for operation (to dimension actuators) is a result of actual experience and measurements from the factorys side, and for given fluids (the most common for apllications for the valve) and with a reasonable safety factor. This factor could be anywhere from (say) 20 to 50 up to 100%.

If the valves sticks dry for a longer periode the necessary loosening torque could be much higer than this, up to 2-5-10(?) times.

The torque is also depending on how thight it is necessary to close the valve to get a dropthight sealing. Wrong closing torque or adjustment of limiting devices could also give a much higher torque than calculated.

Following remarks/personal advice: I would have selected the softclosing PEEK as most equal to existing, whereas a metal to metal seating requieres a high accuracy and undamaged seat over time to close properly. In some cases a metal sealing could be the best choice, but not knowing the application one has to assume that soft-sealing, as existing, is ok.

I would have selected an actuation with gear (either for hand operation or electrical operation). This will both make it easier to get the correct limitation for the closing position and the necessary opening force. In addition the gear could easily be changed or given a 2:1 additional stage if the torque proves to be too low.

 

[zdas04]

Torque on a trunion ball valve is a function of: (1) stem packing adjustment; (2) spring tension on the seats; (3) coefficient of sliding friction between the ball and the seating material; (4) trunion bearing friction; and (5) dP across the valve. Changing seating material only changes one of those five factors, and I would find it quite surprising for a change from Teflon to Peak to create a measurable difference in torque. It could, but I have a hard time making that arithmetic work. I certainly don't think that it could possibly be as much as 15%.

For floating ball valves there is considerable clearance between the ball and the seats so I would not expect any change in torque if you changed the seats from teflon to emery cloth.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[Xun2006]

The valve is NPS 16, class 600, gear operated. Nylon/HNBR seat/seal, change to PEEK seat, inconel x750 spring.

gerhardl,

Your information is supportive and helpful. Thanks a lot.

David,

You answer is what I want exactly, but could you illustrate why floaters does not change, what I think is dP pushes ball to seat hardly that breakaway torque highly depends on the seat material to get friction.

Sincerely,
Xun

 

[zdas04]

I was being dramatic, not accurate. Sorry about that, flamboyance does not translate well to a text-only forum. dP across the ball does energize the seat and breakaway torque from shut to open is significantly impacted by seat material. Breakaway torque from open to shut would be much less affected by material, but the effect is not zero.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"