running-torque_ball valves

[ANTONITO]

Hi guys,

do you know how much does the fluid flow and the turbulences influence in the running torque in ball valves?

Thanks.

 

[Danlap]

Is it Trunnion or Seat supported (Floating)?

(Spindle/stem) torque value on ball valve influenced primarily by:
a. Friction of bearing (which depending on material roughness of Spindle and bearing with or without lubricant/grease) and also diameter tolerance between both
b. Friction of stem with Gland packing (depending on Fugitive Emission tightness class etc. which further influence the Gland retainer torque value)
c. Of course range of designated class (150#,300#, etc.)
d. For trunnion, the spring adjusted (force)Seat should also taken into consideration. And for floating (especially when its located vertically) the weight of the ball.

Back to your question:
Fluid flow? Not sure what you mean with this, if Full Differential pressure applied for sure the Break Open and Break Close torque will have huge impact. As for Running torque, not so much. But it really depending on your design.
Turbulence flow? What application (slurry or super clean)? What is the Reynolds number range? For sure to exactly capture this torque figure you have to simulate this on shop or simply use software.
Then again what is much? it is vary between different design (or even similar design valve) and also process condition

If the purpose of your question is sizing actuator, just add some considerable Safety Factor. Ask your seniors
Rarely see actuator broke first (not before it twist the spindle, force scratch the ball, and so on). So it is almost always over design actuator.

Please be more specific for next question,
Regards,
MR

Greenfield and Brownfield have one thing in common; Valve(s) is deemed to "run to fail" earlier shall compared to other equipments

 

[ANTONITO]

Thank you very much Muktiadi,

This is a trunnion ball valve.

I know how to calculate the break to open torque, as it is an static situation, where of course the points who are important to calculate it are the packing friction, seat-ball friction, and also the pressure force in the ball which is transmitted to the bushing guides.

At the moment for the running, break to close torques,...I am applying a coefficient to the break to open calculation to calculate them; I have obtained this coefficients in some documents that I found surfing internet. My objetcive is to calculate them analytically, but I don´t know the effects of the turbulences, the flow,...

In my case the fluid is crude oil.

I would be very pleased in any help that you can give in the field.

Thank you.

 

[Danlap]

I never done analytical approach for this measurement, and also its not quite practical (and safe) to mount torque-meter when the valves are in operation.
So normally you can obtain this whenever the right actuator are used (which can measured torque / friction). For instance Rotork IQ series

Only did it twice for two different Ball valves (both are 6" and 8" Class 300#) at laminar condition and turbulence (didn't know the parameter, it was just vibrating heavily).
Operate between 5% to 10% Opening. and to be honest the Running torque for both flow are the same.

Then again, with mounted actuator and see the result on the control room it involves more or less 20 variables.
And the stroke are not quite representative for whole cycle.
I would say at any flow characteristic (assuming the service is clean), it will not cause considerable affect on the running torque.

However it may be different if:
- Your crude oil bring some dirts and got trapped between the seat and Ball, small yet can be seen particle will have impact on the torque
- Small sizes valve (below 4 in.) at high Pressure (above 900# Class)
Maybe someone else have better experience and more conclusive summary.

It would be interesting to see your summary from analytical point of view.
regards,
MR

Greenfield and Brownfield have one thing in common; Valve(s) is deemed to "run to fail" earlier shall compared to other equipments

 

[gerhardl]

ANTONITO, Muktiadi:

I agree with Muktiadis last posting. With the large number of variables influencing any theoretical formula for torque, it will be difficult to find a correct mathematical setup including all variables. The variation and differences for each singel factor from valve to valve (at each physical location) will easily vary very much.

Please also be reminded that it is not unusual to observe a very wide range of breaking torque (as indicated by yourself) from valve to valve and application, and the same, in a much lesser degree, also in closing torque.

Reminder: it is normal to stop closing travel for ball-valves with limit switches, torque switches for closing travel to be set higher than normal closing torque to give extra protection.

Depending of fluid and application, break away torque can vary as much as 1:5 (some says 1:10), for crude oil perhaps more normal 1:2. Even if travelling torque will vary less, a valve used first time after a longer periode in open or closed position will normally have a somewhat higer travelling torque than one regularily opened and closed.

One way solve your problem could be to simplify the calculation to some fewer variables. You could for instance limit fluid characteristic to what is used in your plant, and limit other variables to a suitable number, trying to pick out the main influencing ones.

If you include an extra correcting constant and/or describe an expected accuracy and check it out statistically with practical measurements, you would probably hit target with a valid formula usable for similar applications.

Dont forget variation in torque cuased by stem sealings and bearings, and mechanical influence of gears and components in the actuator, and influences from the orientation of the valve.

Good luck!