How to Select Filter Elements

Image Credit: Applied Industrial Technologies

Filter elements are used to remove impurities from liquids. They are used in water treatment systems and fluid processing applications. Filter elements differ by type, and use either organic or synthetic filtration media.

Particle Sizes and Levels of Filtration

When selecting filter elements, buyers need to consider the relationship between particle sizes and levels of filtration. In addition to filtration grade, key performance specifications include maximum liquid flow and maximum pressure.

Types of Filter Elements

The GlobalSpec SpecSearch database provides information about micro filers, ultra filters, and nano filters; reverse osmosis (RO), return line, and cartridge filtration products; as well as bag house elements and wire mesh filters.

• 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-color 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.

Organic Filtration Media

Some filter elements use organic filtration media.

• Activated carbons are 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.

Resources

Norchem - Get Green ROI

ChemicalProcessing.com - Liquid Filtration