The Filter Element is the central component in a filter, where the actual filtration takes place. The key filter parameters such as retention capacity, dirt holding capacity and pressure loss are determined by the Filter Element and the filter media used. May be paper, wire mesh, special cellulose, inorganic plastic, or a combination
Filter elements may be divided into two classes: surface and depth.
Surface filters are made of closely woven fabric or treated paper with a uniform pore size. Fluid flows through the pores of the filter material and contaminants are stopped on the filter’s surface. This type of filter element is designed to prevent the passage of a high percentage of solids of a specific size.
Depth filters, on the other hand, are composed of layers of fabric or fibers, which provide many tortuous paths for the fluid to flow through. The pores or passages must be larger than the rated size of the filter if particles are to be retained in the depth of the medium rather than on the surface.
Filter elements may be also classified as:
Media to be filtered:
- Liquids
- Gases
Particle size:
- Micro filtration elements have membranes with pore sizes ranging from 0.1 to 10 µm.
- Ultra filtration elements are designed to remove particulates between 0.001 and 0.1 µm.
- Nano filtration elements separate molecules by size and are often used to purify, soften, and de-colour drinking water.
- Reverse osmosis filter elements use synthetic membranes that are permeable to water molecules and impermeable to contaminants.
- Cartridge filters feature a pleated or mesh-like construction and may be disposable or recyclable.
- Bag filter or bag house elements are used in a variety of processing applications. They provide a low-cost alternative to liquid filter elements such as filter cartridges.
Material of construction of media:
- Organic Filtration Media
Some filter elements use organic filtration media.
- Activated carbonsare usually made from bituminous coal or lignite and used in wastewater treatment applications. The material source and mode of activation provide specific end-use properties.
- Activated clay is often used to remove dissolved contaminants such as acids, oxidation by-products, and surfactants.
- Diatomaceous Earth (DE) is a naturally-occurring mineral with high absorption, low bulk-density, and high brightness.
- Cellulose is a natural, plant-based filter material with rough fibers that vary in both size and shape. Types of cellulose include cellulose acetate, nitrocellulose or cellulose nitrate, and regenerated cellulose.
- Cotton, like cellulose, is a highly-efficient filtration media. Cotton’s irregularly-shaped fibers and strong absorption properties provide strength even under wet conditions.
- Other types of filter elements use sand and paper.
- Synthetic Filtration Media
Synthetic filtration media for filter elements include plastics such as polyethersulfone (PES), polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), and polysulfone (PSU).
- PES is a high-performance polymer that provides excellent resistance water and steam.
- PP is a thermoplastic filter material that can be used in outdoor applications because of its resistance to ultraviolet (UV) light, weathering, and ozone.
- PTFE exhibits a high degree of chemical resistance and is often marketed in proprietary classes of materials such as Teflon® (DuPont Dow Elastomers).
- PVDF filters also provide good chemical resistance, but do not perform well at elevated temperatures.
- PVDC offers low permeability to water vapor and gases while PSU afford good dimensional stability.
Choices also include non-plastic materials such as glass fiber, glass wool, ceramics, metal, and porous metal.