Globe valve Thrust & Torque 3

[Isha90]

In Globe valve rotating stem, Gland friction thrust is considered zero, so thrust is less when compared to non rotating/rising stem,but Globe valve non rotating/rising stem, Gland friction torque is considered zero, so torque is less when compared to rotating stem,also Actuator operated[rising stem] torque will be less than hand wheel operated valve [rotating stem],please clarify

 

[gerhardl]

?

 

[Isha90]

Is the above statement correct or wrong please

 

[Danlap]

Hi,
It is not (yet) a statement or a clear question.
The only reason I am commenting this, is that since this kind of question's format kind of asked frequently.

as an engineer (anyway this is eng-tips.com), the simplified systematic general question at least should be as follow:
a. Executive summary/background
What you already know for sure and why do you need the conclusion?
In your case, what do you know the difference between rotating stem vs non-rising stem. And what is the un-debatable meaning of friction?

b. Theory (that may support or against your idea)
Gland friction?? against spindle it will never be zero since there is always axial force.

http://www.valvemagazine.com/magazine/sections/back-to-basics/4683-the-noble-globe-valve.html

c. Your hypotesis (with tangible values please ...)
Comparable friction between type A, type B and type C. And torque calculation
d. Your conclusion

And then to this forum, "is my conclusion right"??
I am not a native speaker for sure, but with that systematic, most likely that people in this forum will still understand your question.
And some courtesy of Hi, thanks... instead of "please clarify". Some people would appreciate this better

Kind regards,
MR

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[Isha90]

Hi,The statement was advised to me, so wanted to verify here whether it is right/wrong
Globe valve rotating-rising stem design has more torque when compared to non rotating-rising stem, due to Gland friction torque.
My doubt is why Gland friction torque was not considered non rotating-rising stem & torque should have been same for both design. Thank you

 

[Danlap]

Hi,

The simple answer is No, that statement is not correct.
If I may adjust it slightly, for actuator sizing both type (sliding and rotating) gland packing friction factor between gland ring vs spindle is neglectable and the approach should be as pragmatic as possible following ISA 75.25.01
Some major reason for this are:
- Packing composition/quality for each valve supplier is conservatively considered different. Therefore, friction factor is also different
- Valve design for each manufacturer is also different. For simplification, most of them apply five gland rings with only three bottom rings perform effective sealing. However, some valve may have different number of rings and or dimension
- Seating stress for packing from lower to higher is rubber(O-ring,etc.) < PTFE (modified, expanded, filled) < graphite < etc.

So how to address, this non-uniformity, from ISA 75.25.01. quote “The procedures below can be used to measure sliding friction in a control valve system with a pneumatic actuator. Before performing the test, packing should be tightened using manufacturer-recommended procedures and the valve should be cycled the specified number of cycles. This method assumes that the friction and spring forces (or torques) at any particular position are the same whether stroking open or stroking closed.”

Ideally sizing of actuator should address all of following:
a.The maximum differential pressure in closed position
b.The maximum static pressure in open condition
c.Dynamic forces on the valve plug during any flow condition
d.The normal friction of the packing and seal ring
e.The minimum pneumatic supply pressure

Compared to other points, point d is normatively smaller in terms of value,

Maybe I am wrong, but if you look at the same ISA (om-which its formula I may not snip), indeed for rotating plug (spindle) the formula is simplified shall compared to sliding spindle. So, I think someone that you’re referring to, is oversimplifying this approach.
Perhaps other within this forum have different view

Kind regards,
MR

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376