We have a semolina silo with an output vent pipe (about 120mm dia) but no filter. It has a coarse mesh to keep out vermin (not that we have any vermin) but nothing to stop dust blowing everywhere when it fills up. Can anyone help with advice on the type of filter (and even a supplier) that we could have fitted? Apparently we had one years ago that we think was made by an employee's mum (knit one, purl one??) but this has long since vanished. Ideally we would like to fit it then periodically maintain it. Your contributions welcomed.

I suspect semolina dust may be flammable (like flour), and thus explosive when well mixed with air? For such dusts, you need to ensure there's no possibility of a static spark and transmission of the flame back into the main silo, where an explosion would result. Even if there isn't an explosion hazard, you need to ensure the filter can't become clogged with the dust, or the silo may become over- or underpressured as it is filled and emptied. So maybe a bag filter, where the bags can be shaken mechanically? They are commercially available.