Thanks to you for your help ;) it's friendly
It's more difficult to think with the internal face without water because gaskets will be great with important surface. Or maybe I don't understand your explanations. Tell me ?
For my experience (no water at down and up surfaces but water at internal and external surfaces), the air gap could be like 1Ám so the surface of the gasket is very small and this can't cancel the torque I see on internal/external surfaces. The weight can't be changed because internal/external surfaces are verticals.