会社のニュース Nominal vs. Absolute Micron Ratings: What Filter Cartridge Buyers Should Actually Know

One of the most common mistakes in industrial filtration is selecting a filter cartridge only by its stated micron rating. Two cartridges labeled “5 μm" can perform very differently because micron rating alone does not indicate how efficiently particles are removed.

A nominally rated filter may remove a certain percentage of particles near its stated size, while an absolute-rated filter is designed to achieve much higher and more clearly defined removal efficiency. This distinction becomes critical in applications such as beverage production, pharmaceutical processing, electronics, chemicals, and high-purity water treatment.

A more useful way to evaluate filtration efficiency is the Beta Ratio, commonly expressed as βx.

The Beta Ratio compares the number of particles of a specific size upstream of the filter with the number remaining downstream. For example, a β10 value of 100 means that for every 100 particles of 10 μm entering the filter, approximately one particle passes through.

This corresponds to a filtration efficiency of 99%.

A βx of 1,000 represents approximately 99.9% efficiency at the specified particle size. Therefore, when comparing high-performance filter cartridges, buyers should ask not only “What is the micron rating?" but also “At what efficiency is that micron rating defined?"

A filter with excellent particle retention is not automatically the best choice if it creates excessive differential pressure.

Pressure drop is influenced by filter media, pleat density, cartridge diameter, viscosity, flow rate, contaminant loading, and total effective filtration area. As contaminants accumulate, differential pressure gradually increases.

If the initial pressure drop is already high, the cartridge may reach its replacement limit quickly, even though the filter media still has unused dirt-holding capacity.

For this reason, a properly designed pleated filter cartridge must balance removal efficiency, filtration area, pressure drop, and mechanical strength.

Another frequently overlooked parameter is dirt-holding capacity. A cartridge with a larger effective filtration area can usually capture more contaminants before differential pressure reaches the change-out limit.

This is why pleated cartridges are often preferred over simple depth filters in applications requiring high flow rates or longer service intervals. However, pleat quantity alone does not determine performance. Poor pleat spacing can restrict flow between pleats and reduce the usable filtration area.

Before selecting a replacement filter cartridge, users should confirm the required particle retention efficiency, flow rate, operating pressure, temperature, fluid compatibility, allowable differential pressure, cartridge dimensions, and end-cap configuration.

For critical processes, evaluating filtration efficiency curves, pressure-drop data, material compatibility, and integrity requirements provides a much more reliable basis than comparing micron ratings alone.

Pullner Filter manufactures pleated filter cartridges, membrane filter cartridges, depth filters, and stainless-steel filtration elements for industrial liquid filtration applications. For technical filter selection and customized filtration solutions, visit pullnerfilter.com.