Water treatment is a science that closely connects to the removal of naturally occurring or introduced pollutants from water.

To get pure and clean water, a series of processes needs to be accomplished. By adopting various filter products and filtration technology, we can eliminate most of the contaminants in water.

What is the absolute rating in water treatment

There is a concept of infiltration, which is called a micron rating. The size at which particles are retained by the filter is indicated by the micron rating. Micron rating can be divided into nominal rating and absolute rating. In this article, we mainly talk about the absolute rating in water treatment.

What is the absolute rating?

The absolute rating shows the ability that a water treatment system can remove the particles. A filter will block 99.9% of particles that are at or larger than the micron level, according to an absolute rating. It is normally expressed in microns (µm) or micrometers (mm). The smaller the number, the higher the absolute rating.

Contrary to the absolute rating is the nominal rating. The fraction of particles at or larger than the nominal rating that will be captured by the filter is expressed as a percentage.

However, the actual efficiency of the system may be higher or lower than the nominal rating, depending on the type and size of the particles present in the water.

What is the absolute rating

There are many factors that can affect the absolute ratings, such as the type of system, the size of the system, and the quality of the water being treated. Whether you are considering the purchase of a reverse osmosis water filtration system or the replacement of your current system, knowing the ratings and different types of reverse osmosis systems that exist can help you to make your decision.

The largest spherical glass particle that will pass through a filter under laboratory circumstances, often given in microns (mm), is the absolute rating or cut-off point of the filter.

It displays how big the pores are in the filter media. Filter media having accurate and constant pore sizes or openings should, in theory, have precise absolute ratings.

The absolute rating represents a nominal efficiency figure, or more precisely, the degree of filtering. Unlike the largest particle that will pass through the filter under operating conditions.

It simply determines the size of the largest glass bead that will pass through the filter under very low differential pressure and non-pulsating conditions.

Many filter manufacturers use similar tests, but the use of nominal ratings has fallen out of favor due to the lack of consistency and repeatability of the underlying method.

What is nominal rating

What is the nominal rating?

Normal rating refers to a measure of the average pore size of a filter element. Nominal means the filter will filter out at least 85% of particles of its rated size.

In other words, a filter rated at 1 micron can be expected to remove 85% of particles 1 micron or larger from the water passing through it.

The Normal filtration grade determines the particle size at which the filter begins to be effective.

It is determined by bubble point testing and is more meaningful than nominal ratings and more realistic than absolute ratings for filter elements with different pore sizes.

What is beta ratio

What is the beta ratio?

The effectiveness with which a specific filter element eliminates particles of a particular size is referred to as the beta ratio. Using the ISO multi-pass test standard 16889:1999, the beta ratio is determined.

In order to perform the test, known-sized particles are first added to the test fluid until it reaches a saturation point. Then, the filter is brought online to remove the particles in a single pass through the element.

Beta Ratio
(x = particle size in microns)
βχ = 2 50.0%
βχ = 10 90.0%
βχ = 20 95.0%
βχ = 75 98.7%
βχ = 200 99.5%
βχ = 1,000 99.9%


Contaminant Challenge (particles/mL) Downstream Fluid Quality (particles/mL) Beta Ratio Percent efficiency
1,000,000 500,000 2 50
50,000 20 95
13,000 75 98.7
5,000 200 99.5
1,000 1,000 99.8


In order to compare the particles that were present upstream of the filter element to the particles that are still present downstream of the element, the testing apparatus tests the hydraulic fluid both before and after the filter element. The beta ratio is the product of the number of particles of a particular size.

The difference between absolute dating and normal rating

Nominal units are used to describe pore diameters. Typically between 60% and 90% of solid particles bigger than the declared pore size, which is typically expressed in micrometers or microns, can pass through a filter with a nominal pore size rating.

Filter retention is greatly influenced by filtration factors such as operating pressure, particle shape, and particle concentration.

difference between nominal and absolute

An absolute pore size rating indicates the pore size at which an organism or particle of a particular size will be stopped by the filter almost entirely effectively (greater than 99.8 percent).

Relative filter products

There are many filter cartridges, filter bags or other filter products, which have been qualified as absolute filtration products. Following are some products we want to recommend to you for your filtration system.


Water filtering can offer easy and potable water for business applications as well as for households. The filtration reduces the content of contaminants such as suspended particles, parasites, bacteria, algae, viruses, and fungi.


Water purification occupies large and important part of filtration field. It is important to do water treatment because every industry and every people need it. When it comes to water, we heartily recommend cartridge filter system for you.

Brother Filtration is a leading solution provider of prefiltration systems. We mainly work on water treatment, process filtration, petrochemical, food & beverage, and lots of industrial areas.

Reverse osmosis

Reverse osmosis is a water purification process that forces water molecules through a semipermeable membrane using pressure.

The water molecules are then trapped on the other side of the membrane, leaving impurities and dissolved minerals behind. This process can be used to purify both fresh and brackish water and often used in desalination plants to produce fresh water from seawater.

Reverse osmosis requires a corresponding pressure to force the water through the membrane. This pressure is supplied by pumps, and the process is typically done in several stages to increase efficiency.

Additionally, reverse osmosis does not require the use of chemicals, which makes it a safer option for many people. If you are looking for a way to purify your water, reverse osmosis may be a good option for you.


Absolute rating is one of the indicators of a filter, it shows the ability to remove the particles. With higher demands from various industries and applications, filter products which are qualified as absolute filtration products are more and more popular in the market. It is essential to figure out what on earth the absolute rating is.

Brother Filtration, as a filtration expert, designs and manufactures all kinds of filter products which includes nominal filtration and absolute filtration.

We aim to fulfill all needs of different industries and applications and try our best to do R&D to offer better filtration solutions. If you have any problems with filtration, please feel free to contact us.

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