How to choose the correct filtration

By Martin Lissenburg, Product Specialist

Wednesday 13 September 2017


The article explains the filter options that are available from IMI Norgren.


What IMI Norgren filters are available?

We have 40µm (General Purpose - Standard Air), 5µm (General Purpose - Clean Air), Oil Coalescing (down to 0.01µm) and Oil Vapour removal filters. The General Purpose filters will remove water, dust and particles from the air to the stated size.

How can I envisage particle sizes?

The µm (micron) sizes above are often difficult to visualise. To give examples, water mist is up to 40µm; pollen to 10µm; cloud and fog to 1µm; insecticide dust to 0.5µm and tobacco smoke and oil aerosols to 0.01µm.

How do I choose the right filter for the job?

Always check the specification of the tool or component to be supplied. Firstly, is the fluid air? This may sound obvious but, clearly, an air filter will not work in a hydraulic system. What is to be filtered? Particles (of what size) and water? Oil droplets (in applications such as air bearings, pneumatic gauges, textile or paper making macinery) or oil vapour? Remember, oil vapour filters only remove compressor gases, not CO, CO2 or other hydrocarbons. We recommend a 5µm filter is used to pre-filter a coalescing filter and the latter should always be used as a pre-filter for oil vapour removal.

Next, consider the environment (for example, are solvents used for cleaning?) and the temperature and pressure of use; this will determine the type of bowl and drain to be employed. Finally, consider the flow requirements for operation; size for flow and not pipe connection and take account of pressure drops though the filter(s) selected.  

It is important not to exceed flow rates though oil coalescing and vapour removal filters, otherwise quality of air will reduce. A tip is that a larger surface area (bigger) filter, of the same µm, will have a lower pressure drop.

How do I ensure continued performance over time?

By definition, filters collect contaminants so they need replacing to maintain their performance. We offer service kits and these should be used at regular intervals. General purpose filters require servicing every 12 months and the same frequency is advisable for coalescing filters. Vapour removal filters should be serviced every 1000 hours at 210C. This reduces as temperature increases; for example at 380C, the time reduces to 200 hours. 


More information

Find out more by viewing our range of filters.

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