A funnel is a long hollow tube or pipe, generally wide in the middle and narrower at the other end, usually used for guiding the liquid or powdered powder from one fluid to another. Funnel filters are made of brass, aluminum, glass, or even plastic. They are often used in food processing plants, pharmaceuticals, or military applications. Funnel filters may also be called paper mills, screw pumps, or vacuum pumps. There are basically two types of these filters: spiral and spin tubular.