Crankcase ventilation

[JohnFol]

Morning all, inlet manifold off car so taking opportunity to clean some stuff up, buy new pipes and so on.

One thread here suggested cleaning out the ventilation valve. There's a 13mm nut that releases a cover where the pipe from crank case enters and pipe to airbox exits. I was expecting something inside the cover, something like wire mesh or a filter.
There is a bit of wire mesh wedged in pipe near air filter, but I can't see the point of this "cover" otherwise
Any ideas?

[HFStuart]

The design inside acts as an oil separator  - the larger blobs catch and drip back down while the vapour passes through. The tricky bit is the little elbow hose which fails and the 'new' ones I've tried perish quickly. There is also more than one size for no very good reason that I can work out.

[WestonE]

The Mesh in the pipe is a flame catcher so clean it and re-fit.

Eric

[JohnFol]

Thanks chaps. I've ordered replacement pipes but why they have different diameters at each end I'll never understand