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Micron Rating. What are they and why is it important?

The Filter Guys

What is a Micron?

A micron is a measurement of size. It is one millionth of a metre (1/1000000m) or a thousandth of a millimetre (1/1000mm). In filtration, a micron rating is a rating of the media’s capacity to stop dirt (it is not an efficiency rating). The micron rating will be nominal or absolute.

A nominal micron rating means that a media may be explained as 10 micron but that is a mean average, it probably varies between 5 and 15 micron over the surface of the media itself; this often applies to cellulose media which is a natural product. Engine oil and fuel filters are often nominally rated.

An absolute micron rating means that the media has a uniformed surface and will ‘do what it says on the tin.’ A 10 micron absolute filter will not allow particles of 10.1 micron or bigger through at all. Absolute filters are man made products, such as glass fibre, and are manufactured to an extremely high specification. Hydraulic filters are often absolute rated (but not necessarily for all hydraulic applications).

Why is it important?

In filtration the micron rating of the element is very important to guarantee its correct operation. The wrong type of media can mean more dirt gets through the filter than you want and this can cause wear and tear and even complete breakdowns of your engines and hydraulic equipment.

Take a lubrication system on your engine. Oil is pumped between the moving parts of the engine, this oil contains particles, if the oil isn’t filtered before being sent into the engine then wear and tear will occur. The space between moving parts may only be 30 or 40 microns. If oil contains particles of that size then dirt is going to jam and consequently build up between moving parts. Over many hours (or years) of operation with inadequate filtration this build up of dirt will cause the moving parts to jam which will cause catastrophic failure of an engine leading to expensive downtime and repair costs.

Of course, over time filters will clog with dirt too but they are easily sourced from Sterling Filtration Ltd and replaced. They hold the damaging particles so the engine doesn’t have to. A filter may cost ten, twenty, fifty, one hundred pounds and sometimes even more, but compared to the cost of downtime of a machine and the stripping and rebuilding of an engine they are easily the most cost effective way of keeping your engines and machinery running properly all of the time. See your operators manual for service intervals.

Watch Out for Dents on Liquid Filters.

The Filter Guys

Watch Out for Dents on Liquid Filters. Cracked filters can be caused by dents made during improper installation. Filters that are dented prior to or during installation should not be used. Filters dented after installation should be replaced immediately. The cost of replacing a dented filter is much less than the cost of the damages that could result from a dented filter that fails during service.

Filter fatigue results from pressure pulses within the system. Pressure is regulated by a pressure regulating valve. This valve is spring operated and intermittently opens and closes to regulate pressure. Once pressure exceeds the setting of the spring in the regulating valve, the valve will open and relief the pressure until the spring can expand and close the valve. This function is continued continuously during operation of the system, creating a pulsing effect. Filter canisters are subjected to the same pulsation. However, unlike the spring in the pressure regulating valve, canister material is susceptible to failure after such fatigue.

Filters are designed with a low carbon steel to resist fatigue and are formed so the stress created by the pulses in the system are equalised over the surface area of the canister. A dent provides an area of stress concentration where pressure pulses can greatly shorten the fatigue life of the canister.

Remember, filters should never be fitted to an engine or hydraulic system if they are dented or damaged in any way.