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

In parts cleaning systems, filters are usually implemented through the use of an external filtration “loop.”  Cleaning or rinsing liquids contaminated with particles are removed a tank or other vessel through a pipe fitting located, ideally, at the lowest point in the vessel.  Locating the collection fitting at the lowest possible point takes advantage of the natural tendency of most particles to sink to the bottom.  The collection fitting is connected to the inlet of a pump which, in turn, is connected to the inlet of the filter device.  Once the liquid has passed through the filter, the filtered liquid is returned for continued use in the cleaning or rinsing process.  The removed particles remain trapped in the filter.

The actual working part of the filter is called the “filter media.”  The filter media is usually enclosed in a filter housing which is designed so that the media or “cartridge” can be removed and replaced when necessary.  Filter media is constructed of different materials and is configured in various ways depending on the application.  Some common materials of construction are paper, cotton and other natural materials and a wide variety of plastics.  How these materials are configured into a filter determines the flow capacity of the filter and the volume of particles it will be able to contain.

The above has only scratched the surface of what there is to know about filters and filtration.  Upcoming blogs will provide more detail on how various filters work and how proper filter media selection can improve the effectiveness of filtration and extend filter life.  Proper and adequate filtration is crucial to the success of any cleaning process.  It has been said that there can never be too much filtration in a cleaning system.  Stay with me through this series and we’ll find out.