agc wp-astonishing facts about filter elements part 1

Astonishing Facts About Filter

Elements, Part 1

WHITE PAPER © 2017 AGC Refining & Filtration LLC

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



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.



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



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



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



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.



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.

www.AGCInternational.com

3045 East Elm Street

Springfield, Missouri 65802, USA

Toll Free: +1 800 865 3208

Phone: +1 417 865 2844

agc wp-astonishing facts about filter elements part 1

Sales