This white paper discusses filter element testing and performance. It explains that micron ratings assigned by manufacturers are arbitrary and not a reliable way to compare filters. The standardized beta ratio test actually counts particles before and after filtration to measure a filter's efficiency at removing various sizes. The multi-pass test determines a filter's solids holding capacity and removal efficiency over time by continuously monitoring pressure and particle counts as dust is added. Combining different filter elements can improve overall filtration efficiency by leveraging their complementary properties.

1. Astonishing Facts About Filter
Elements, Part 1
WHITE PAPER
© 2017 AGC Refining & Filtration LLC

2. AGC REFINING & FILTRATION
ASTONISHING FACTS ABOUT FILTER ELEMENTS, PART 1 2
Contents
Micron Ratings 3
Standard Tests 3
The Multi-Pass Test 5
References 8

3. AGC REFINING & FILTRATION
ASTONISHING FACTS ABOUT FILTER ELEMENTS, PART 1 3
Micron Ratings
If you could take a piece of paper and slice it in 75 very thin sheets, each sheet would be 1 micron
(micrometer) thick.
Figure 1: Relationship of Particle Sizes by Diameter
The filter industry is in a state of confusion about rating their filters. Customers want a simple way to
compare filter elements so the micron ratings system was invented. A micron rating is an arbitrary value
assigned to a filter by the manufacturer, not an actual measured value. It quotes a particle size without
establishing the filter’s efficiency at removing that size particle.
Since the micron rating cannot be verified, filter manufacturers feel safe in assigning any number that
they want. It is not recommended to use micron ratings to compare filter elements.
Standard Tests
To compare filters, the filter industry has established standardized tests for measuring performance. The
most frequently used method is the beta ratio test (SAE J1858). This test measures the element’s
efficiency to remove specific particle sizes. The test actually counts the particles in the fluids before and
after the element. This ratio is called the beta ratio.
For instance:
The beta ratio will generally be between 1 and 75.

4. AGC REFINING & FILTRATION
ASTONISHING FACTS ABOUT FILTER ELEMENTS, PART 1 4
Beta ratios can be converted to efficiencies by the following formula:
Beta ratios are the most accurate way to compare the performance of filters.
The figure below illustrates the beta ratio concept by showing the upstream particles to be more
numerous and diverse than the downstream particles.
Figure 2: Upstream Particles Versus Downstream Particles

5. AGC REFINING & FILTRATION
ASTONISHING FACTS ABOUT FILTER ELEMENTS, PART 1 5
The Multi-Pass Test
The multi-pass test is a standard test that is used to determine the solids-holding capacity and the solids-
removal efficiency (beta ratio) of a particular filter element.
Figure 3: Multi-Pass Test Basic Operating Principle
Test dust has a known particle size distribution (number and sizes of the particles), which is determined
with a particle counter. The test dust is mixed in a test fluid and the mixture is pumped through a filter
element.
During the test the differential pressure of the filter element, the upstream and downstream particle
counts, and the amount of added test dust are continuously monitored. The test is terminated when a
certain differential pressure across the filter element is reached or the beta ratio falls below a certain
level.
Figure 4 shows that as the differential pressure increases and more solids accumulate on the filter, the
beta ratio decreases.
Figure 4: Relationship Between Differential Pressure and Beta Ratio

6. AGC REFINING & FILTRATION
ASTONISHING FACTS ABOUT FILTER ELEMENTS, PART 1 6
This illustrates the problem with the standard beta ratio test. The filter element’s efficiency is actually
increasing as filtration proceeds (it filters better as time goes on) and the differential pressure across the
filter element is also increasing as more and more solids accumulate on the surface of the element. This
progression is shown below for 1-micron, 5-micron, and 15-micron solids particles.
Initially, all 1-micron and all 10-micron particles get through. After some time, only 1-micron particles get
through. The differential pressure increases as the element begins to plug up.
Table 1 shows the relationship between beta ratio values and increasing efficiency.
Table 1: Beta Ratio Values and Increasing Efficiency
Beta Value Efficiency # Upstream # Downstream
2 50.0000% 100,000 50,000
4 75.0000% 100,000 25,000
10 90.0000% 100,000 10,000
20 95.0000% 100,000 5,000
40 97.5000% 100,000 2,500
60 98.3333% 100,000 1,667
75 98.6667% 100,000 1,333
100 99.0000% 100,000 1,000
125 99.2000% 100,000 800
150 99.3333% 100,000 667
200 99.5000% 100,000 500
300 99.6667% 100,000 333
500 99.8000% 100,000 200
1,000 99.9000% 100,000 100

7. AGC REFINING & FILTRATION
ASTONISHING FACTS ABOUT FILTER ELEMENTS, PART 1 7
2,000 99.9500% 100,000 50
4,000 99.9750% 100,000 25
5,000 99.9800% 100,000 20
10,000 99.9900% 100,000 10
20,000 99.9950% 100,000 5
50,000 99.9980% 100,000 2
The type, shape, and size of solids in the fluid to be filtered has an important effect on efficiency. No
single filter element can have an optimum removal for all these material forms. Experience has shown
that overall filtration efficiency can be improved by combining different types of filter elements. The
different properties of the elements complement each other; the upstream element removes specific
solids that would otherwise end up on the downstream element. For instance, a stainless steel, back
washable strainer can be used to remove solids 10 microns and larger, thereby extending the life of the
second filter element.
The stainless steel strainer shown here is available in standard sizes from 10 to 100 microns. It can be
backwashed and used indefinitely unless physically destroyed.

8. AGC REFINING & FILTRATION
ASTONISHING FACTS ABOUT FILTER ELEMENTS, PART 1 8
References
1. AFI Archives. 1957–1999.
2. Allen, Albert. “Depth Filtration.” 1975.
3. Allen, Albert. “Standard Filter Element Tests.” 1957.
4. D’Andrea, Thomas. “Filter Performance.” 2003.
5. Johnston, Peter. “Particle Size Distribution in Arizona Test Dust.”’ 1999.
6. Johnston, Peter. “Validation of a Filter Cartridge.” 2003.
7. Viljee, Abbas. “Standardized Test Dust.” 2003.

9. www.AGCInternational.com
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