Understanding Filters ..Media’s and Microns
Filtration for the internal combustion engine has seen many changes since the days of no filters, bag filters and large cartridge filters. Available space, an increase in under bonnet temperatures, chemical changes to oils and fuels, oil pressures and volumes, fine/ultra-fine filtration, global emission control laws and landfill requirements are but some of the industry changes encountered during the past 5 decades. The reduction of filter size meant focusing on filtering media, surface area and flow rates. Various technologies have unfolded. Wix has an interesting ability to pioneer change, from concept to production.
Micron, micron rating
Interesting terms but what do they mean? A micron is a unit of measure, in fact one millionth of a metre in size. Sometimes you hear people ask about a particular filter, what is its micron rating? Also commonly thought is the lower the number the better the filtration. Oil, fuel, hydraulic (industrial fluids) filtration performance and efficiency are not measured in terms of micron rating.
The filtering media through which a given fluid passes is measured by multi-pass Beta testing. Under test, measured amounts of test particles are added regularly to the fluid which is pumped continuously through a filter and measured samples of fluid are taken at timed intervals upstream and downstream of the filter. The Beta (β) ratio is calculated by dividing the number of inlet particles of a given size by the number of outlet particles of a given size. Here is a simple calculation:
Dirty side (Inlet) particles = IN
Clean side (Outlet) particles = OUT
If IN = 200 and OUT =100, then
200/100 = 2
β = 2
The old adage question about a filter’s efficiency: What is the micron rating of your filter? …can be simply answered, a micron is a unit of measure, one millionth of a metre in size not a measure of efficiency. The efficiency of a filter is measured in terms of multi-pass Beta testing as defined above…not its micron rating.
Filter media is the medium or material through which fluid (oil, fuel etc.) passes to capture harmful contaminants in suspension. Liquid filter media’s today use many different materials and combinations depending on their application. Early day’s filtration used hessian bag material, some bypass filtration used wood chips and cotton waste, others used news print. Traditional filtration uses cellulose (filter paper) for fluid and air filters. Other organic media’s are used but many have turned to inorganic media’s such as poly’s and or glass fibres, composite or blended media’s, even wire supported. Medias used in various European applications have synthetic fibres which are more durable, less susceptible to embrittlement and have greater dirt holding capacity. Others again use non-disclosed proprietary medias for special purpose applications including removing acids in oils (sequester) and water removal. Various automotive and heavy duty oil and fuel filter manufacturers have moved away (somewhat) from spin-ons (screw-on filters) due to issues with landfill. As a consequence ‘Eco friendly’ smaller cartridge filters (no metal parts) are commonly used particularly in today’s automotive applications.
Certain late model passenger vehicles (especially European) have liquid management systems which utilize a filter module. It comprises cooling ability through a heat exchanger, a thermostatic controller, oil pres control and filtration all in a unitized plastic module.