A constructed cartridge somewhat different from those just described is the lenticular disc filter – the prime difference being that the components of a complete element are capable of undertaking filtration on their own, and are in fact used in that
way. The lenticular disc is a circular element made from two discs of filter mediu joined around their outer edges and separated at the centre by a filtrate offtake tube, to give the disc the shape of a lens for which it is named. The disc can be used independently, in an appropriately shaped housing, but more often several discs are mounted one above the other (as in Figure 3.58) on a common filtrate pipe, and then placed in a cylindrical housing as a cartridge. This format has been successfully used by Cuno for its ZetaPlus charged media filters.