Metal seated ball valve with tungsten carbide coating - lapping procedure

[Wonlek Chua]

Hi,

we have a 12" tungsten carbide coated ball valve here for servicing. ball condition is fine as it has only minimal use on site.
So we start lapping to the ball on machine.

I would like to ask:
- what is the lapping sequence for achieve good sealing? I am thinking: machine lapping to bring the spherical roundness within 2 tau (0.050mm) difference, then, lap using PTFE block + very fine diamond powder on machine to achieve mirror-surface on the ball.

Then, hand match-lapping to seat. Blue Test to check sealing area.
And finally, hand match lapping using PTFE block + very fine diamond powder locally on sealing surface.

What do you think?

 

[jameslander]

Hi, we would recommend:

1. Lap on machine to generate roundness – Could use Diamond or Boron Carbide for this stage
2. Use the ball seat and face the seat with ASFL polishing pad material and use a combination of 3µ diamond compound and a 3µ diamond slurry to polish the ball.
3. Blue check seat against ball