What Are the Types of Precision Air Filters?

1. Classification by Filtration Efficiency

Coarse filter: Captures particles 5 μm and larger with an efficiency of approximately 35%. It is often used as a prefilter in HVAC systems and large air compressors to remove larger dust particles, hair, fibers, and similar contaminants.

Medium-efficiency filter: Captures particles 1 μm and larger with an efficiency of 60%-95%. It is often used upstream of a high-efficiency filter or for primary HVAC filtration and effectively removes pollen, smoke, bacteria, and other contaminants.

Sub-high-efficiency filter: Captures particles below 1 μm, with efficiency rated using 0.5 μm particles. It can be used as a terminal filter in a cleanroom and removes finer dust, viruses, and other contaminants.

High-efficiency filter: Designed for particles smaller than 1 μm and used as a principal terminal filter in cleanrooms. Its efficiency is rated at 0.3 μm. It removes most fine airborne particles, including bacteria, viruses, and pollen, and provides highly clean air.

Ultra-high-efficiency filter: A further refinement intended to achieve air-cleanliness targets for particles from 0.1 to 0.3 μm, with efficiency rated at 0.12 μm. It is mainly used where exceptionally clean air is required, including cleanrooms for semiconductor manufacturing, biopharmaceutical production, and precision-instrument manufacturing.

2. Classification by Structure

Panel filter: A simple design made from flat filter media such as nonwoven fabric or mesh. It offers low resistance and low cost, but relatively low efficiency and dust-holding capacity. It is commonly used for coarse filtration.

Air filter - panel filter

Pleated filter: The media is folded into corrugations to increase filtration area, efficiency, and dust-holding capacity. It can be used for coarse, medium, and some high-efficiency filtration.

Air filter - pleated filter

Bag filter: Consists of filter bags and a frame. The bags are generally made from nonwoven fabric, glass fiber, or similar materials. A large filtration area, high dust-holding capacity, and low resistance make this design suitable mainly for medium-efficiency filtration and as a prefilter for high-efficiency filters.

Air filter - bag filter

Separator-type high-efficiency filter: Uses ultrafine glass-fiber paper as the filter medium, with aluminum foil or paper separators dividing the pleated media into multiple airflow channels. It offers high efficiency and low resistance but has a relatively large volume. It is commonly used in cleanrooms and other areas with strict cleanliness requirements.

Air filter - separator-type high-efficiency filter

Separatorless high-efficiency filter: Uses hot-melt adhesive or another bonding material to hold ultrafine glass-fiber paper in pleats without separators. It is compact, lightweight, and easy to install, and is widely used in cleanrooms, clean benches, air showers, and other purification equipment.

Air filter - separatorless high-efficiency filter

3. Classification by Application

Outdoor-air treatment filter: Used to treat incoming air in a clean HVAC system. Different grades are selected according to requirements, while chemical filters are added when chemical pollutants must be removed. It primarily removes outdoor dust, pollen, harmful gases, and other contaminants to supply clean fresh air indoors.

Indoor supply-air filter: Usually a sub-high-efficiency, high-efficiency, or ultra-high-efficiency filter, sometimes combined with chemical filtration. It serves as terminal filtration in a clean HVAC system, ensuring that supply air meets the required cleanliness level for health and comfort.

Exhaust-air filter: Installed in an exhaust duct to prevent cleanroom pollutants from entering the atmosphere. It generally uses a sub-high-efficiency or high-efficiency filter, or a combination of high-efficiency and chemical filtration, to protect the environment.

Filter for equipment inside a cleanroom: Supports internal circulation to maintain the required cleanroom grade. It generally uses high-efficiency or ultra-high-efficiency filtration, sometimes combined with chemical filtration, to preserve cleanliness and protect equipment from contamination.

Filter integrated into manufacturing equipment: Built into production equipment. Because manufacturing requirements vary widely, these are generally custom filters designed to remove specific airborne contaminants and protect product quality.

Air filter for high-pressure piping: Used for gas transmission at a pressure of 0.1 MPa. Its media and structure differ from those of other filters. It removes contaminants from high-pressure gas and protects piping and equipment.

4. Classification by Special Function

Activated-carbon filter: Uses the adsorption properties of activated carbon to remove odors, volatile substances, bacteria, viruses, paint spray, smoke, and many other airborne pollutants. It is often combined with other filters.

Air filter - activated-carbon filter

Antibacterial filter: Incorporates an antibacterial agent into the media or uses material with inherent antibacterial properties. It suppresses the growth and reproduction of bacteria, viruses, and other microorganisms, removes harmful airborne microbes, and creates a healthier air environment.

Air filter - antibacterial filter

Oil-removal filter: Specifically designed to remove oil mist and oil contamination from compressed air. It is generally made from multiple layers of glass fiber, activated carbon, or similar materials and can reduce oil content to an extremely low level. It is suitable for food processing, pharmaceuticals, electronics, and other applications with strict compressed-air oil limits.