Estimate Seating / Unseating load of a 1" Full Port Ball Valve

[fcce]

Hello everyone,

I wonder if anyone could help me on this issue: I am currently performing design basis revision of air operated valves, and I need to obtain the values of Total Seating / Unseating torque and Total Closing / Opening torque (from 0º to 90º stroke) of a 1" Full Port Ball Valve with a design basis differential pressure of 50 psi.It may be obtained from a test under dynamic conditions, but unfortunately there is not any test made. I have found some information in XOMOX catalogues, but it is not exactly what I am searching. Maybe anyone could provide me with some estimated values you have dealt with.

Any comment on this issue would be much appreciated.

Thanks in advance.

 

[JLSeagull]

I don't have a table for Xomox.

A table for Apollo lacks all of the detail suggested. The Apollo tables reflect the valve size and working pressure, with an adder for option 24, perhaps the stem or seat selection. Request the required data from a Xomox peddler.

Looking at the Apollo tables, the values are the same for NPS 1.5 using the 87A100, 87A140, 87B100, 88B100 compared to the 1 NPS for 87A200 and 88A240. Looking at the data for other sizes there is a consistent size shift between the tables with the same data on different sizes. The 87A100, 87A140, 87B100, 88B100 at 6 NPS matches the 87A200 and 88A240 at 4 NPS. Perhaps the models reflect reduced port valves against full port valves. I could look into this but have not. The adder for option 24 has the same shift in values. The highest torque for each size is in the LSST column at about twice the zero psig data.

(BTW, I request the seating, unseating and running torque to be furnished with quotations on automated valves in a table compared against the actuator torque using the minimum air supply and a safety factor.)

 

[JimCasey]

You will find wild variability dependent on a large number of parameters.

Seat design: material, preload, cross-sectional profile
Ball diameter, surface finish, surface plating
Differential pressure, lading material

It is customary to size the actuator to supply an adequate torque margin to handle the seating/unseating torque throughout the travel of the valve. In reality, the seating/unseating torque is pretty high due to (1) maximum DP occurs at this point (2) the surface of the ball engages the full periphery of the seat(s) (3) Stiction will likely occur from the valve being left in the closed position for prolonged times. Running torque drops to as little as 60% because stiction, contact area, and differential pressure effects are all diminished. There is another torque spike near full open as the edge of the port passes over the edge of the seat(s). Breakout torque from full open is almost as high as opening torque because the stiction force and the full distorted seat friction are there. Only the differential pressure effect is missing and that is partially offset by the fact that the ball is NOT loaded and in contact with both the upstream AND downstream seats.

If the lading in the valve is a lubricating liquid the torque can be very low. Torque is higher for a "dry" liquid, higher yet for a gas, and even higher for a slurry.

After the valve is in service the torque can continue to rise because of plating of corrosion products on the ball, particles embedding in the seat, degradation of the surface finish of the ball.

So you asked a simple question but there is not a simple answer.

 

[fcce]

I really appreciate your comments, JLSeagull. I will try to get the information required from the vendor, in this case.

Thanks again.

 

[bcd]

fcce,

One fact to consider is the friction torque of the stem packing. If this small ball valve uses a stem nut to compress the seal, the packing torque can be as much as 50 - 70% of the torque required to operate the valve. The friction torque from the packing does not vary as much as the seta torque does when the valve unseats. Probably the best option for this case is to the analysis with constant torque. Don't attempt to predict the difference between seating and run torque on such a small ball valve. A technican with a wrench tightening a stem seal will quickly obliterate your analysis.

bcd

 

[fcce]

Thanks for your comments, JimCasey, I assume it is not easy to find a particular answer for my question, so I would like to ask you about any valve manufacturer who can provide me with some of the data I need.

Your explanation is perfect from a theoretical point of view, which I really appreciate, but in this moment I am interested in getting specific data on this issue, i.e., approximate values of torques that might be obtained from an in situ test carried out in the Plant.

In order to clarify a little bit more my request, here are the operating conditions of the valve:

DN = 1" Full Port Ball Valve 3 pieces
Maximum DP = 50 psi
Type of fluid = Gas (Air & Steam)
Max. Fluid Temperature = 347 ºF
Fluid density = 0.168 lb/ft3
Max. Upstream pressure = 50.01 psig

I have attached two XOMOX pdf documents with a valve very similar to the one I am talking about. I hope this helps.

Thank you in advance.

 

[valvehowker]

FCCE,
Are these ball valves from a defunct valve maker. Are they all the same? What are the seat materials?

Do you need the torques at different temperatures eg under normal and fault conditions?

Cordially
Bill H

 

[belowzero]

FCCE,
If You need 'Actual' working torques on the plant, get yourself a torque transducer, this is placed between valve and operator(may have to make a new mounting kit or adaptor) but it is far the best way.
We have used one for years to obtain this information at various temperatures and pressures and works well, in fact there are a number in the field which monitor the increase in torque on the valves to indicate when service is required.
B

 

[fcce]

Valvehowker, the manufacturer of these valves and their actuators is CONTROMATICS, which dissapeared many years ago. I have tried to get in contact with Flowserve staff since I know they currently own the data related to these equipments. To date, I have not been able to find what I really need, so I will really appreciate your comments on this issue.

Actually, I am dealing with two types of ball valves, but they only differ in the nominal diameter: 3/4" and 1", the operating conditions are the same in both valves, and as I said yesterday, they are very similar to those XOMOX models I uploaded on my previous message.

The seat material is Viton® fluoroelastomer.

I do not need the Seating / Unseating / Running torques at different temperatures, because the operating temperature remain more or less constant. Actually, I am considering the maximum DP of design basis conditions (50 psi), which is what determines the performance of these valves.

Regards

 

[gerhardl]

fcce : As usual Jim Casey has provided, in my opinion, the best answer. Even with the exact figures you are giving, this will be no mathematical excercise. The only way to get reasonable figures is to test as close to operational conditions as practical.

As an actuator supplier/fitter even we have experienced, with equal valves at 'equal' conditions, that the practical resulting torque may vary as much as 1:2 or 1:3 or even more, given some differences in valve inner tolerance or actual, real process conditiones, if starting from actual process or after a dry standing periode etc.

A valve manufacturor will give you a torqe based on 'normal' operating conditions, stating clean fluid, no sticking or drying residues and often with temperature limitation.

This figure, when/if given out, will at least have an included 20% safety margin, often 50-100%.

As fitters we often see necessary to select, even then, an actuator one size larger to be sure of operation under all conditions, landing at 4-5 times the 'theoretical' torque.

For different type of fluids for the same valve the torque may at least vary by factor 1:10 in practical life.

Any chance you can convert from a theoretical to a practical approach by testing out one smaller and one larger actuator, or recommending an 'oversized' actuator if this is a critical application?

 

[JimCasey]

Contromatics is not part of Flowserve.
According to the Circor website: Contromatics is part of Circor. Under the KF division.

http://www.circor.com/index2.html

 

[belowzero]

Be careful not to go over the stem yield torque when over sizing the actuator, it won't take much to shear a 1" valve stem.
However as this appears to be an installed valve that already operates I doubt over sizing or re-sizing actuators is a requirement.
B