[Doc Watson]

John,
I will look into that but will the material still degrade if there is a few coughs and spits of flame?

Danimal,
Yes my thinking on the subject exactly..... although a new method of attaching them to the stacks would be required if they were hemispherical....unless they were formed with a flat lip.

Jim,
Given twice the area wouldnt it increase the unrestricted flow to 75%? still much better than 50%.

I've talked to the supplier and they can plasma cut the mesh which 'welds' the edges of the wire together to prevent them falling apart.

Forming the mesh into a 'dome' shape wouldnt be a problem would just make a 'mould' (male and female parts) and the wire should form into shape easily.

Im still not to happy about the rubber seals which hold the screen filter, but will get some mesh and have a play with it to see what works and what dosent. Im also thinking about producing a split collar which could hold the mesh in place but will initially use flat wire mesh (the first one I quoted).

Then try using the rubber holders with a domed mesh, and if all else fails devise a split collar to hold a domed mesh.

Andy