Technical on Washing Air Filters
Numerous changes have occurred with internal combustion engines over the past 5 decades. Carburettor & spark ignition engines relied on contact points in the HV distributor to be clean, dry and correctly adjusted for the engine to run properly. Now, non-serviceable electronic control modules are the initiator for spark ignition. Diesel engines used mechanical injectors and a mechanically timed in-line fuel pump with cam operated plungers and barrels. Today it’s hydraulically actuated electronically controlled unit injectors delivering highly atomised fuel at 10 times the pressure into a high compression combustion chamber.
During this 50 year period the engine’s air filter has also undergone many changes. Early air cleaners used Oil Bath or Steel Mesh, then dry phenolic resin Paper Type. But now the Dry type media has changed; heavy duty air filter media used to be Amber in colour, now it’s White. A “traditional” phenolic (amber) resin is still used in some air filters. However in heavy duty it is uncommon today. Typically a more traditional phenolic resin package will be used when more water ingestion is a concern. With a “traditional” phenolic resin package, the media is subjected to high heat for a specific period of time. Heat curing set the resins and as a byproduct causes the resins to darken (brown up). The media structure, materials and manufacturing processes have changed; hence White media is commonly used instead of Amber media in today’s heavy duty air filters.
Filter media comes in an uncured state which is then processed before being cured. (This is reverse to cooking spaghetti – it doesn’t bend before it is cooked – simply it breaks). Fibres are very different today. Structure and density of media is more sophisticated – some use overlay, some have density that increases through its depth. Fibres used to be measure in thousands of an inch, now it’s a billionth of an inch – eg nanos. Air filter manufacturers are always striving to achieve 99.9% + efficiency. Sophisticated fibres, sophisticated structure and sophisticated ways are used to hold the structure (media).
When looking at dirt in an air filter, it’s the dirt trapped deep inside the structure that’s the concern, not the dirt on the surface. Washing it, tapping it or shaking it doesn’t remove all the dirt.
In the photo above, the air has to find its way through the mat of fibres, starting by entering the open fibres at the top and working its way through much denser material at the bottom. As the air (with airborne dirt) works its way through and into the media, dirt is trapped. When the dirt is trapped, it blocks off a path and air has to choose a new path. As these paths are being plugged off it becomes more difficult for air to pass through – this is called restriction, which is measurable. This process continues until so many paths are blocked, the air has too difficult a time finding ways through the fibre mat and the level of restriction (restriction indicator) conveys it’s time to service the air filter. In this instance the engine struggles to breath, emits black smoke and/or uses more oil and fuel. As per the photograph the dirt you would see on the surface of the top of the media is not where narrow tight paths are plugged. Rather, the capacity and efficiency are the result of the entire depth of the media. When the filter becomes restricted, it is because dirt has plugged paths throughout the entire depth of the media. Washing the media (reverse flushing) in an attempt to liberate the dirt from the depth of the structure tends to be more problematic. This can damage the bonding ability of the resins, causing fractures and altering the fibers within the media structure. This damage may not show up when inspecting used elements with a light bulb and the unaided eye. Then, if a filter with damaged media is placed back in to service, the force of the air pushing and pulsating its way through the structure can exploit the damage and result in ruptures or at the very least, lower efficiency capabilities. If you could get all the dirt out, fibres will have been damaged and the structure of the media compromised.
- When a washed or cleaned air filter is put back into service there will be a higher level of restriction and termination is reached sooner. In any event the washed/cleaned filter must be removed at 25” of water (restriction) regardless of service life and how it appears. (See point no 12)
- Most failures (media failure) occur in service, not when checked with light at cleaning.
- Washed/cleaned filters create a propensity to be over-serviced, which in itself is strongly discouraged by equipment and filter manufacturers. Every time an air filter is removed or disturbed from its housing there is the likelihood of dirt entering the clean air intake, this being the principle purpose of an inner filter when used.
- This results in more downtime, labour and inventory. Ie: dirty filters waiting to be cleaned, filters being cleaned, filters on hand that have been cleaned, this all equates to higher running costs.
- Has the environment been considered? Washing uses a large amount of water and the detergents could be absorbed into the waterways. Does the company that is washing filters have a stringent environmental policy?
- Air Filter Performance;
If any 1 of these things are changed – the others are affected. If Initial Restriction is increased, capacity is reduced. (EG: If a 5 litre bucket has 3 litres in it, another 2 litres is the maximum that can be added before it’s full.)
- Engine technology and servicing procedures have changed dramatically in the last 50 years and filter media has followed accordingly.
- Today’s heavy duty media is not designed to be wet, shaken or blown out.
- The so-called cost savings of washing/cleaning is lost in over-servicing and savings are negated by the complexities and costly hidden pitfalls and inefficiencies.
- No OEM or filter manufacturer’s warranty covers an air filter once it has been cleaned. An excerpt from the North American ‘Filter Manufacturers Council’ technical service bulletin 89-4 states: “Heavy duty air filter element manufacturers do not recommend any type of cleaning process be used on their products. Further, they do not warrant their product once it has been cleaned”.
- Therefore, there is significant risk involved; does the company who cleans the filters have the financial backing and sufficient insurance cover in the event of a claim?
- Servicing & monitoring engine air filters is correctly managed by observing the air restriction indicator, (like any other dashboard gauge) not by how the filter appears, distance travelled, hours run, time or habits.
- Air filter washing is a dated, inefficient procedure for those with spare time, space, money and prepared to take a gamble. The modern fleet owner needs efficiency, reliability and warranty coverage.