Hydraulic Filter Beta Ratios Explained: What B10 >= 1000 Actually Means

A hydraulic filter rated B10 >= 1000 lets through no more than 1 particle of 10 µm or larger for every 1,000 that reach it, which is 99.9% capture at that size. The number comes from one laboratory test, ISO 16889, and it only means something when you know the particle size, the beta value and the test standard together. A micron figure on its own tells you very little.

Below: how beta is measured, how to convert it to efficiency, and how to read the ratings on the 805 hydraulic elements in our catalogue that carry one.

How the beta ratio is calculated

The beta ratio is a simple division. Count the particles at or above a chosen size upstream of the element, count them again downstream, and divide the first number by the second.

• Formula: Bx = particles >= x µm upstream / particles >= x µm downstream
• Worked example: 600 particles of 7 µm and larger upstream, 4 downstream. 600 / 4 = 150, written B7(c) = 150.
• Efficiency: (1 minus 1/B) x 100. B7(c) = 150 gives 99.3% capture of particles 7 µm and larger.

The subscript is the particle size, and the size is part of the rating. "Beta 1000" without a size is meaningless, because every element reaches beta 1000 at some particle size. A coarse element might hit it at 40 µm, a fine one at 5 µm.

The test standard reports results at fixed beta values: 2, 10, 75, 100, 200 and 1,000. Manufacturers quote the particle size at which their media reaches each of those values. When a data sheet says "7 µm(c) at B >= 1000", it is telling you the smallest particle size the media stops at 99.9%.

Converting beta to efficiency

The relationship between beta and efficiency is not linear. Going from beta 2 to beta 10 takes you from 50% to 90%. Going from beta 200 to beta 1000 only moves efficiency from 99.5% to 99.9%. That looks like a small gain until you count what passes through.

• B = 2: 50% efficient. 50,000 of every 100,000 particles pass.
• B = 10: 90% efficient. 10,000 pass.
• B = 75: 98.7% efficient. 1,333 pass.
• B = 200: 99.5% efficient. 500 pass.
• B = 1000: 99.9% efficient. 100 pass.

Moving from beta 200 to beta 1000 at the same particle size cuts the number of particles getting through by a factor of five. Hydraulic oil passes through the filter over and over, so that difference compounds with every pass.

This is the problem with ratings like "10 micron nominal". They carry no beta value, so you cannot tell whether the element stops half of the 10 µm particles (beta 2) or 999 in 1,000 of them (beta 1000). Without a beta value attached, the micron number is a description, not a rating.

What the ISO 16889 multi-pass test does

ISO 16889 is the multi-pass test used to produce beta ratings for hydraulic elements. The rig circulates test fluid through the element in a closed loop. A controlled stream of test dust (ISO Medium Test Dust) is injected upstream at a fixed rate, and automatic particle counters sample the fluid upstream and downstream throughout the run.

The run continues while the element loads and its differential pressure climbs to a set terminal value. The reported beta is an average across the run. The same test also produces the element's dirt holding capacity: the mass of dust it retained before reaching terminal differential pressure.

The "(c)" in µm(c) tells you the particle counters were calibrated to ISO 11171. That calibration replaced an older method used with the earlier test, ISO 4572. The two calibrations size particles differently, so a "10 µm" result under ISO 4572 and a "10 µm(c)" result under ISO 16889 are not the same particle size. When you compare two elements, check that both ratings carry the (c). An undated beta figure with no (c) came from the old test and cannot be compared like for like.

What the beta ratio does not tell you

The multi-pass test is run under steady flow at a constant temperature. Real hydraulic systems have flow surges, pressure spikes, cold starts and vibration. A beta rating is a controlled comparison between elements, not a promise of what the element does on your machine.

Beta changes over the life of the element. The reported figure is an average. Machinery Lubrication gives the example of two elements that both average beta 300. One starts at 700 and falls to 200 as it loads. The other starts at 50 and climbs to 700 as the dirt cake builds. Averaged, they look identical. In service, the second one lets far more contamination through in its first hours, which is exactly when a freshly serviced system needs protecting.

Beta stability is a separate rating. Some data sheets state the differential pressure up to which the element holds its beta. "Beta 200 stability = 210 psid" means the element stays at or above beta 200 at the rated size until it reaches 210 psid (about 14.5 bar) across it. If a data sheet gives this figure, use it.

Beta says nothing about dirt holding capacity, collapse pressure or flow. Two elements can share a 10 µm(c) B >= 1000 rating and differ widely in how long they last before the bypass valve opens. Check the collapse rating against your housing. Pall's Ultipor III data sheet, for example, gives 20 bar collapse for its pressure line elements, 10 bar for return line and 207 bar for its high-collapse non-bypass elements.

How manufacturers encode the rating in part numbers

Many element part numbers carry the micron grade in a letter or number code. Reading it saves a lot of guesswork when the label is worn.

• Pall Ultipor III: the media grade letters KZ, KP, KN, KS and KT. Pall's data sheet rates them at B = 1000 at 2.5, 5, 7, 12 and 22 µm(c) respectively. In HC9100FKN13H, "KN" is the 7 µm(c) grade, "13" is the nominal length in inches and "H" is nitrile seals ("Z" would be fluorocarbon).
• Hydac BN4 (Betamicron): the two digits before "BN4" are the filtration grade code, so 1.12.13 D 03, D 06, D 12 and D 25 BN4 are the same element in four grades.

Both codes can describe the same element. Our aftermarket replacement for the Pall HC9100FKN13H is rated 7 µm(c) in pleated glass fibre, 70 mm outside diameter, 34 mm bore and 330 mm long, and it also replaces the Hydac 1.12.13 D 06 BN4. If your old element shows a code from another brand, our compatibility and cross-reference page explains how to match it.

Reading the ratings in our hydraulic range

Of the hydraulic elements in our catalogue, 805 list a filtration rating. They fall into three media groups, and the media tells you a lot about how the rating should be read.

• Inorganic microfibre (glass fibre), 541 elements: almost all at four grades. 5 µm (100 elements), 7 µm (92), 12 µm (179) and 25 µm (148). This is the media used for multi-pass rated pressure and return line elements, and these grades match the ladder most hydraulic manufacturers publish.
• Impregnated paper (cellulose), 112 elements: 10 µm and 25 µm. Glass fibres are smaller and more uniform than natural cellulose fibres, which gives glass media more dirt holding capacity size for size. Paper is the lower cost media, and the micron figure on a paper element should not be read as equal to the same figure on glass fibre.
• Wire mesh, 161 elements: 10 µm to 250 µm, with 25, 40, 60 and 90 µm the most common. Mesh is a surface strainer with a fixed opening size. It is used for suction strainers and coarse protection, where the aim is to stop large debris without restricting flow to the pump.

When you replace an element, match the media type as well as the micron figure. Swapping a 10 µm glass fibre element for a 10 µm paper one lowers the real filtration even though the number on the label is the same. Swapping a suction strainer for a fine glass fibre element can starve the pump.

Of the elements where we publish a collapse pressure, the three common values are 10 bar (113 elements), 20 bar (108) and 210 bar (78). The 210 bar elements are built for non-bypass housings where the element has to survive full system pressure. Never fit a 10 bar return line element in a high-pressure housing just because the dimensions and micron grade match.

Choosing a rating for your system

Start from the most contamination-sensitive component on the circuit. Servo and proportional valves are the usual limit, which is why non-bypass, high-collapse elements are fitted in front of them. Each component manufacturer states a required ISO cleanliness code for the fluid, and that code is the real target. The element grade is chosen to hold the fluid at that code, and an oil analysis tells you whether it does.

If you are replacing an element that already works, keep the same grade and media. Going finer than the original raises differential pressure and shortens element life, and in a housing with a bypass valve it can mean the element spends more time in bypass, which defeats the point. Our guide to choosing an industrial oil filter covers the dimension, seal and bypass checks, and when to change an industrial oil filter covers clogging indicators and service intervals.

You can browse elements by micron rating and media in the hydraulic filter collection. If you have a part number we do not list, send it through the quote request form and we will check it against our cross-reference data.

Frequently asked questions

Is B10 >= 1000 better than B10 >= 200?
Yes, at the same particle size. Beta 1000 lets 1 particle in 1,000 through, beta 200 lets 5 through. That is 99.9% against 99.5% efficiency, and five times fewer particles reaching your components.

What does the (c) in µm(c) mean?
It shows the particle counters were calibrated to ISO 11171, the calibration used with the ISO 16889 multi-pass test. Ratings without the (c) come from the older ISO 4572 test and size particles differently, so they are not directly comparable.

Can I compare a 10 micron paper element with a 10 micron glass fibre element?
Not on the micron figure alone. Ask for the beta value at that size under ISO 16889. Glass fibre media also holds more dirt than cellulose size for size, so it lasts longer between changes.

Does a higher beta ratio mean the element lasts longer?
No. Beta measures capture efficiency. Service life depends on dirt holding capacity, element area and how much contamination enters the system. A finer element can load up faster on a dirty system.