Nominal or Absolute Filtration: What Do You Apply to Your Fluid?

When selecting the right filter for your application, it’s essential to understand which type of filtration is right for you: nominal filtration, absolute filtration, or both.

• Definition: Absolute filtration retains all particles larger than the specified micron rating.
• Example: A 10-micron absolute filter does not allow any particles larger than 10 microns to pass through.
• Efficiency: ≥ 99.98% (Beta 5000)

• Definition: Nominal filtration retains a certain percentage of particles at or above the specified micron rating.
• Example: A 10-micron nominal filter may capture only 60% to 99% of particles larger than 10 microns.
• Efficiency: Lower than absolute filtration—typically between 10% and 99%, depending on various factors such as flow rate, differential pressure, particle type, size distribution, and concentration.

Nominal filters have a Beta ratio between 2 and 100, depending on design and application.

In comparison, absolute filtration starts at Beta = 1000 (99.9%) and goes up to Beta = 5000 or higher.

The Beta ratio indicates how effectively a filter captures particles.

Examples:

• Beta 2: 1 out of 2 particles passes → 50% efficient
• Beta 1000: 1 out of 1000 particles passes → 99.9% efficient
• Beta 5000: 1 out of 5000 particles passes → 99.98% efficient

Although the percentage difference may seem small (e.g., 99% vs. 99.98%), Beta 5000 is 50 times more effective than Beta 100.

• Typical Efficiency: A nominal 0.5 micron filter typically removes 10% to 60% of particles 0.5 microns and larger.
• No Guarantee: The filter does not capture all 5-micron particles.
• Efficiency Loss Under Pressure: As differential pressure increases, more particles may pass through, depending on the type of contaminant and structure

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