Gas tight surface 1

[ketrab88]

HI,

I've been having a problem with gas tight valve. Two rotary parts. The surface on the cooperating parts Is Ra 0.03 Rz 0.7 - I thinkt hat it's too rough. Everything seems ok with water, but when we start testing it at 1000 bar Nitrogen, starts bubbling. I fiugred out now two solutions:
1) Grind both parts to Ra 0.02-0.04 Rz 0.1-0.2 with strcuture direction after grinindig concentric (c) so gas will be trapped inside those circles.

2) Have worse surface roughness like on Ra 0.8 like on the flanges ( serrated ) and try to lap them together, but I think it will not work. We tried to lap it with better surface and it was not gas tight.

BR,
Bartosz Wereszczysnki

 

[ketrab88]

It's my first post so sorry for all missing information. Couldn't find the option to edit my previous post so I will just add some info below.
Test temperature is - Room tempreature, around 21C.
Test pressure for seats is 1034 barg, but it's start leaking at 100 barg.
Valve type: Rotary Gate Valve.

Does/Has anyone have/had similar problems ? Any suggestion that might be a surface ?

I'm sorry for mess in this post, but hopefully everything will be more clear now.

BR.
Bartosz Wereszczynski

 

[Compositepro]

Metal-to-metal valve seats can never be considered to be bubble tight. If they are once, they will not be for long.

 

[gerhardl]

Metal- to metal seated valves might be 'gas thight' depending on definition/test type, and also, ref.compositpro, for certain periode and operating circumstancs.

Anyway: you describe this as a rotary valve without describing the sealing geometry. Thightness is not only a function af test pressure and roughness, but also how or what pressure keeps the rotating sealing surface agianst the seat sealing. If this is an eccentric rotating valve,is it as much a function of a very precise three-dimensional sealing geometry.

It might even be that a rougher sealing surface, correctly formed in area and geometry might give a better sealing than a finer surface. Please note that this advice is given without any experience for this valvetype and pressure.