The primary motivation to develop pleated membrane cartridges was the need of an increased in the filter area sufficient to secure the engineering advantages of lower applied differential pressure and larger volume flows. Achieving this goal in the pleated filter cartridge form means, moreover that less planned space needed to be allocated for filter installations.
It is not easy to complete a filter membrane, as it can break or be damage, such instances were experienced during the development of these filter units. To avoid the potential brick of pleating, the pleat density, respectively membrane area was restricted. The filtration area is achieved within the cylindrical pleat pack which was resin bonded to the endcap.
Polyester material was commonly used as pre- and support fleece. Both, the polyester and the resin used to bond a membrane to the end cap were reason for the low chemical and thermal resistance of such filters, not to mention extractable levels, which would be unacceptable in today’s standard. The first membrane materials were cellulose acetate, cellulose nitrate, polyamide, and polyvinylidene fluoride (PVDF). Often, these membrane materials were surfaced treated to achieve pleatability, wettability, and stability of the membranes, which required large water flush volume to remove leachable from the filter matrix before the filter could be used.
Pleating polymeric membranes has been a major achievement due to the possibility of pleat breaks, which happens once so often if the right pleat parameters, methodologies, and chemical composition have not been found. Unique treatment during the pleating process are required to be used to make sure the pleating is performed without potential damage. Furthermore, the pleat edge are required to be robust; otherwise, the membrane could be damaged during the filtration process, for example, due to pressure pulse or water hammer.
Nowadays, Teflons (PTFE), PVDF, polysulfone, polyethersulfon, nylon, etc are also available for pleated filters. Depleting arrangement, the back and forth folding of the flat membrane filter upon his self, permits the presentations of a large filters surface area within a small volume.
Typical construction components of the pleated filter cartridge are as follows:
Endcaps are the terminals for the cartridge and the pleat pack and are responsible for holding the cartridge contents together. The endcaps are also responsible for providing the seal for the membrane pleat pack between upstream and downstream side of the filter. Also, the adaptors which are used to fit the filter element into a filter housing are welded onto the endcaps. Polypropylene endcaps are frequently adhered to the membrane pleat pack, by ultrasonic welding, which is the current status quo and most robust weld form.