Sorting Out Filters – The Basics

Many topics can’t be covered in a single, one page blog entry.  For this reason, some of the more involved topics will be discussed in several sequential blogs with a common theme.  This is the start of one such series about filters and filtration.

In parts cleaning, filtration is applied to liquids used to clean and rinse parts as well as to air used to dry parts after cleaning.  Many, but not all, of the terms and principles related to filtration apply to both liquids and air.  This series will specifically discuss filtration of liquids.

The goal of many parts cleaning applications is to remove particles of various sizes and descriptions from the surfaces being cleaned.  Once removed, the particles must be segregated to prevent them from being re-deposited on subsequently cleaned parts.  This segregation extends the useful life of cleaning solutions and rinses.  Filters are used to remove solid particles.  The concept is quite simple yet, as with many things, there is a lot more to know than most people realize when it comes to filtration.

A filter is no more than a barrier which selectively holds back solid particles by making it physically impossible for them to pass.  We are familiar with filters from everyday use.  The filter in your coffee maker, for example, is designed to hold back the coffee grounds while letting the extracted essence of the coffee continue on to be enjoyed in your daily dose of “Joe.”  A window screen is another kind of filter.  It will keep mosquitoes out of your house but would not be very effective at holding back coffee grounds if you tried to use it in your coffee maker.  Chicken wire fence, another “filter,” will contain chickens but wouldn’t be an effective barrier to mosquitoes or coffee grounds.  Filters range in various grades from “fine” to “coarse.”  A “fine” filter will hold back smaller particles than a “coarse” filter.  Ratings are usually given in “microns” and indicate the minimum size particle that will be contained by the filter.

Illustration of Filter Loop