The so called "W bank" is a particular kind of vane pack used when the reduction of the lenght of the tank is a priority.
Thanks to its paritcular "V" shape it's possible, with half lenght of the pack, to obtain the requested crossing area to guarantie the performances requested and, at the same time, to reduce the dimension of the vessel.
The W bank mantains all the characteristics and qualities of normal vane pack and so it's possible to assembly packs with different style of vanes or stick on a wire mesh agglomerator to increse the performances of separation.