Air Filters

Air Filters are systems or components that remove particulates from air as it passes through filtering elements and can be complete systems or replacement elements alone. Key specifications include the intended application, physical size, filter type, filter media, and air flow rate. Air filters are used in systems that require particulate-free air. They are used also to clean the air before exhausting it. An air filter system usually consists of a filter element and the housing that contains the element. They come in shapes for specific applications such as automobile engines, clean rooms, range hoods, or furnaces. An air filter can remove a variety of filtrands including dusts, fumes, oils, and bacteria.

Electronic Filters

Electronic Filters are used primarily to process electronic signals by removing unwanted frequency components or enhancing others. They usually operate at frequencies below RF (radio frequency). Typical operating frequencies ranges are AF (audio frequency) or IF (intermediate frequency), both of which are power frequencies. There are many types of, and functions for, electronic filters including passive or active, analog or digital, and low pass and high pass. Electronic filters are also used to minimize or eliminate electrical noise.

EMI/RFI Filters

EMI/RFI Filters are electrical devices that eliminate or minimize EMI (electromagnetic interference) or RFI (radio frequency interference) within a system. Key specifications include the intended application, filter type, electrical characteristics including voltage, current, and frequency ratings, as well as bandwidth. EMI/RFI filters are used primarily in electronic and telecommunication applications to minimize or eliminate EMI or RFI signals that interfere with the performance of an electrical product or system. The filter is normally placed between an AC power line and the equipment requiring protection. Versions can also be placed on PCBs, incorporated in connectors, or used as stand-alone components for mounting in utility cabinets. The filters may also work to eliminate EMI/RFI emissions from the equipment.

Fluid Filters

Fluid Filters are devices or systems that remove unwanted substances from fluids as they pass through the filtering elements. They may include complete systems or the replacement elements alone. Key specifications include the intended application, filter type, filter media, filtrate and filtrand, particulate size, and flow rate. Fluid filters are used primarily in any system that requires the fluid to be free of particulates or debris, either to protect the equipment or to clean the fluid before it is discharged into the environment. A fluid filter system usually consists of a filter element and housing. They come shaped for specific applications, such as engine oil filters, cooling system filters, and metalworking fluid filters. The filter media can be made of a variety of materials including cloth, foam, carbon, sintered metals i.e. stainless steel, etc.

Fuel Filters

Fuel Filters are devices that remove unwanted materials from a fuel system as the fuel passes through it and may include a complete system or the replacement element. Key specifications include the intended application, filtrate, particulate size, and flow rate, as well as the physical dimensions. Fuel filters are used primarily to filter debris or unwanted substances from fuel to protect the equipment as well as allowing the fuel to burn more efficiently. The filters are usually designed for a specific application, such as a diesel or aircraft engine, or for the filling of tanks, etc., and are available in a variety of shapes and sizes depending on the required application.

Hydraulic Filters

Hydraulic Filters are devices or systems that remove contaminants from hydraulic fluids and may include complete systems or the replacement elements alone. Key specifications include the filter type, filter material, and the physical dimensions. Hydraulic filters are used primarily for filtering unwanted debris or contaminants from fluids for use in hydraulic cylinders or with other systems that use hydraulic fluids. Depending on the application, the filters may require different materials or types. Components often remove particulates.

Optical Filters

Optical Filters are devices placed in the paths of light sources to allow only specific wavelengths to pass or be transmitted. Key specifications include the intended application, material, wavelength characteristics, and physical dimensions. Optical filters are used primarily in photographic applications but can be used in other scientific or technical work as well. Many types of optical filters can be found including UV, infrared, or band pass, among several others each having a specific function, allowing a specific wavelength or range of wavelengths to be transmitted. Some are specific to photography and may not be applicable in technical work.

RF and Microwave Filters

RF and Microwave Filters are electrical devices that either block or pass specific frequencies. Key specifications include the intended application, filter type, and frequency characteristics. RF and microwave filters are used primarily to process electronic signals by removing unwanted frequency components or enhancing others. They usually operate at radio frequency ranges (megahertz and gigahertz) and at microwave frequencies. Various types of filters area available including low pass, high pass, band pass, as well as reject pass, each having a specific wavelength, or range of wavelengths, that is either blocked or transmitted.

Water Filters

Water Filters are devices or systems that remove contaminants from water and may include complete systems or the replacement elements alone. Key specifications include the intended application, flow rate, particulate size, and the physical dimensions. Water filters are used primarily in any system that requires the water to be filtered or cleaned to remove debris and particulates. Many applications use water filters including water parks, refrigerators, aquariums, wastewater facilities, etc. The filters are available in various sizes and types depending on the application.

Applications and Industries

Filters that process fluids such as air, fuel, water, hydraulic oil, etc. generally rely on paper, foam, or other similar materials whose pore sizes can be controlled to pass only materials below certain sizes. Designs are many and varied, including baffled, pleated, spiral wound, finned, etc. Filters are often replaceable and are sold as complete assemblies of housings and filtering elements, or are available as elements only. Filters tend to be application specific. Household water filters are a common representation of the housing/cartridge design. Other filtering systems are designed to be cleaned, such as sand filters used for water filtering which are often backflushed to restore capacity.

Types

The Engineering360 Spec Search database provides information about micro filters, 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 filtrationelements have membranes with pore sizes ranging from 0.1 to 10 µm.
• Ultra filtrationelements are designed to remove particulates between 0.001 and 0.1 µm.
• Nano filtrationelements separate molecules by size and are often used to purify, soften, and de-color drinking water.
• Reverse osmosisfilter elements use synthetic membranes that are permeable to water molecules and impermeable to contaminants.
• Cartridge filtersfeature a pleated or mesh-like construction and may be disposable or recyclable.
• Bag filteror 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 clayis 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.
• Celluloseis 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).

• PESis a high-performance polymer that provides excellent resistance water and steam.
• PPis a thermoplastic filter material that can be used in outdoor applications because of its resistance to ultraviolet (UV) light, weathering, and ozone.
• PTFEexhibits a high degree of chemical resistance and is often marketed in proprietary classes of materials such as Teflon^® (DuPont Dow Elastomers).
• PVDFfilters also provide good chemical resistance, but do not perform well at elevated temperatures.
• PVDCoffers low permeability to water vapor and gases while PSU afford good dimensional stability.