5 things you didn't know about air filters

In this blog we describe five facts about air filters that you probably didn't know yet.

Secondary filter is not what it seems

One of the most common mistakes is to think that the secondary filter provides extra good and additional filtration. But did you know that this filter is much coarser than the primary filter and that only your primary filter protects your engine against the most harmful small contaminants in the air?

The function of the secondary air filter is to protect your air intake duct in case you remove the primary filter from the housing. When you remove your primary filter, for example to replace it, there is still a lot of dust and contamination in your air filter housing. In addition, a lot of dust falls from your primary filter when you remove it. Of course, you don't want this dust to get into the intake duct to your engine. For this you have the secondary filter.

You often replace the secondary filter 3 times less than the primary filter. So you can safely leave the secondary filter in place for the first two maintenance sessions. Especially now that you know that in the normal process it adds nothing to the quality of the air going to your engine.

A used filter is better than a new one

This is one that deserves a little explanation. You would say that you should replace an air filter because it loses its effectiveness over time. Nothing is less true. Of the total contamination that an air filter allows through during its entire lifespan, 10% occurs in the first operating hours. This sounds strange because you would expect that nothing filters as well as a clean filter.

The reason that a used filter works better than a new one is that the first layer of dust and contamination on the filter media ensures even better filtration. This first layer of pollution often consists of somewhat coarser dust particles. As a thicker layer of coarser dust particles forms on the filter media, this layer helps to capture the smaller dust particles.

The efficiency of an air filter increases throughout its lifespan. So you may be looking at a filter where you can no longer even see the filter material due to all the collected dust, but it still functions better than a new filter.

Why and when should it be replaced? Only when the filter is completely clogged and does not allow enough air to pass through should you replace the filter. You will notice this in practice if the performance of your engine decreases because it does not get enough air. You obviously want to avoid this point, also because it is bad for your engine, but how do you know when this moment has come? The easiest thing to do is to install a sensor or indicator that simply indicates this for you. This is an investment that is always worth the money. It prevents you from replacing filters too early. This allows you to avoid unnecessary costs and also prevents you from installing a new filter too often, while your current filter actually does its job better.

How much air passes through your filter

Your air filter is the only filter that prevents dirt from the air from entering your engine and cylinders. In the air intake system, all air to the engine also goes through your air filter. Quite an important task. If you consider that to burn one kilogram of diesel you need about 15 kilograms of air, you can already realize that this is quite a bit of air in volume.

As an example, a small diesel engine with a cylinder capacity of 3.5 to 4 liters and approximately 100 HP uses about 7 cubic meters of air per minute. This is 7000 liters per minute, or about 115 liters per second!

Just for reference, if you drive 100 kilometers with a car that consumes 1 in 10, about 100,000 liters of air pass through your engine in these 100 kilometers. This is a slightly simplified calculation, but it clearly shows what an air filter has to purify and what it is exposed to.

This air consumption becomes even higher, especially with modern engines. Turbos and compressors provide extra air in your engine for more efficient combustion and higher performance. This higher air pressure during combustion also means that even more air is consumed. As a rule, you can say that a turbo engine needs about 30 to 50% more external air. This air also enters through your air filter.

100 grams of dust is enough to destroy your engine

Of course, this depends somewhat on the size and cylinder capacity of your engine. Roughly speaking, you can say that to irreparably damage the engine of a normal passenger car, only 50 to 100 grams are needed to completely destroy your engine. For larger engines, for example tractors and excavators, this is approximately 100 grams. If you go to the really extremely large engines, think of mining trucks, then you may be talking about 200 grams, but this will not be much more.

This is quite little if you consider that you see the dust passing by in large clouds on construction sites and that 5 to 10 thousand liters of it pass through your filter per minute.

It is better not to clean

There is quite a bit of discussion about whether cleaning your filter is possible or not. The most recommended method to clean your air filters is with air pressure. If, despite our advice, you still want to clean your filters with air pressure, never use more than 5 bar pressure. It is even better to forget about cleaning with air pressure altogether. An air filter is the only protection you give your engine between the dusty environment and the combustion in your engine. When you clean, you must be very careful not to damage the filter. You can easily recognize a crack, but it is difficult to see the small damage in the filter media.

The material that you filter from the air, fine dust, often consisting of very fine silica particles, is so fine that you can hardly see them with the naked eye. Let alone that you can visually inspect the filter media after cleaning and be sure that no damage has occurred anywhere that allows these small particles to pass through. If you also consider that it is the smallest dust particles that cause the most damage to your combustion chambers and engine in the long term, then it is strongly not recommended to blow your filters clean. It is also the case that you cannot estimate what kind of filter material is blown away with the dirt. The collected silica or dust is so sharp and hard that it can easily damage your filter media if blown away.