Not really familiar with the model, size and pressure class you are talking about, but I would recommend to consult with the manufacturer. Otherwise it would be trial and error attempt with likelihood that you might alter its integrity.

Reason as follow, in simplified manner:
Tightness (better leakage rate) for all sealing components e.g. gasket vs groove, disc vs seat are depending on three main factors: seating stress, elasticity modulus and geometry (for example: if one applies force towards let say O-ring/round edge, is it going to be effectively sealed against let say chamfered chamber? Or is it better with wedge shape). Hope you get the idea for Plug versus seat.
I assume that this valve is actuated, and you already perform some method of lapping? Or in other words the angle of contact between Plug and seat is not OEM standard any longer.
Main mechanical constraint: stem/spindle strength, and brittleness of Plug/seat's hard facing (Tungsten carbide/stellite/some sort)
Actuated: stem thrust is already pre-calculated by manufacturer considering seating stress and constraints above.

Therefore, by making it more flat, valve requires more thrust to generate higher seating stress in order to achieve current leakage rate (Class III). And even bigger force is required to achieve better leakage rate. Sometimes the direct consequence is that the Hard facing will start to crack.
Changing flatness or geometry might also have impact on its Cv.

Mirror finishing is good target for refurbishment attempt, but not necessarily will make the leakage rate better,

Wish you good luck,
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&f...

I agree with Danlap the best solution to would be to contact the manufacturer. The disks should be lapped together. Seating stress in the MC-10/20 setup is provided via the rotator and is dependent upon upstream pressure. The lower the upstream pressure the lower the seating force. One way to ensure consistent seating force would be to load the disks via wave spring. It doesn't look like Cameron offers this option. The M1A line of angle chokes looks like the disks are loaded by the carrier and the outlet flange at bolt up.

Hi Danlap and SPDL310, thank you for your comments. In the fact, we are manufacturer for wellhead and now try to develop this style inline choke valve. I would like to clarify if the discs should be lapped each other by face to face. Even we made the surface to achive 0.00004" flatness (2 light band). Looking forward to hearing again.

Hi booob630,
I am still guessing in the dark over the design, and can only re-collect bits and pieces from you and SPDL310.
So you are the manufacturer of the wellhead, but are you the manufacturer of the valves or even better do you have the 3D drawing and technical design calculation of the valves?
If I were you, Yes I would lap the disc and seat. Measure the final angle of seating contact. Assemble valve and seat test it with proper torque value and upstream pressure. Measure the leakage rate (assuming this is still Class III). All of this parameter would be you first reference.

Go to the finite element analysis software e.g. Abacus. Incorporate all of your data above e.g. spindle thrust force, upstream force, modulus young of your seating material (ceramic/TC/Stellite/??) at design temperature, etc. You or the programmer will see the elasticity of the seat and its theoretical seating force. This seating force is corresponding to above leakage rate (Class III).

And then, still using the same software, increase the stem thrust (provided by the rotator??) gradually which would increase the seating stress. See until which force the seat material will break. Any force below that breaking point (which acknowledge by your engineer consider as safe), to be applied on the actual valve.
See whether the leakage rate is improving.

How to apply higher thrust? This is depending on the actuation force, e.g: as SPDL310 suggest, add springs, etc. More handwheel turns??
IMO it is better (faster and cheaper) to assess the theoretical stress first. Rather than lapping, shatter the seating contact, re-coat, re-lapping, with small chances of success.
If you cannot achieve better leakage rate even with above method, then most likely the geometry of the seating contact is not suitable for such tightness.
Retrofiting the trim is the last option. IMI or CCI have good experience to perform this.

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&f...

If its an MC Valve from Taylor, i don't think they are rated for direct application to a wellhead as they are not API 6A rated.