In a blog to commemorate the 75th anniversary of MANN HUMMEL, Mario Rieger, manager for the development of air cleaners in Truck Business division, adds some interesting aspects to the history of the cyclone separator. Today cyclones are fitted as pre-separators for air cleaners in construction site trucks, agricultural machines and in railway locomotives to lengthen the service life of the filter.
Cyclones have been around for hundreds of years. Each small carpenter’s workshop has a cyclone on its roof to separate the wood shavings from the air created during sawing. Even the building where my office is located has three huge cyclones over five metres high on the roof.
On the top of this article you can see some pictures of a rusty historical cyclone which most likely belonged to a carpenter’s workshop. An inventive person of that time improvised his own cyclone. Not much was required for this. He only needed an old oil barrel and a pipe attached tangentially to make a cyclone in an oil Barrel.
The difference at MANN+HUMMEL is that we build cyclones for the pre-separation of dust, primarily for trucks, agricultural machines and railway locomotives, wherever an engine is operated in a dusty environment. Compared to the oil barrel, the cyclones we manufacture today have a complex design which is the result of a considerable amount of time and money and the brainwork of our engineers – even though the fundamental principle remains the same.
Air in the truck cyclone swirls at over 200 km/h
In terms of flow, the principle of the cyclone pre-separator is not dissimilar to the cyclone storms found in India or the Fijian islands in the Indian Ocean. The difference is we pack the cyclone into a housing and use the resulting centrifugal forces to separate particles.
Just as in the feared weather cyclones, only the air turns in the cyclone pre-separator. In order to ensure a strong rotation, it isn’t even necessary to use a blower on the truck as the engine itself is a big air pump. Each minute a large truck engine can easily suck in 36 cubic metres of air. This is a substantial amount of air corresponding to the volume of a 3 by 5 metre sized bathroom. The air in the cyclone then rotates at more than 200 km/h. Since the dust particles are heavier than air, it is mainly the coarse particles which are thrown to the outside by the centrifugal force. The coarse particles are then directed to the ambient air outside the housing via a discharge valve.
A guide vane is fitted in the air flow path which causes the air in the cyclone to rotate. In this process the air flows inline through the guide vanes of a fixed propeller so that the air is forced to rotate.
If there is not sufficient space for such a pipe cyclone, we use a cyclone block. Here we combine many small cyclones in a housing, which, for example, may require less space behind the driver’s cabin.
High speed, high separation
Cyclones in trucks are not used in highway applications, but on construction site vehicles exposed to high dust levels. The rule here is that a faster rotation speed of the air through the cyclone will result in better separation of the dust. On the other hand, a high rotation speed also results in a high pressure drop. This is a balancing act which is particularly relevant for construction site trucks because ultimately the aim is to reduce fuel consumption. Therefore a compromise is made between high separation efficiency and low pressure drop. But this is still enough to lengthen the service life of the paper filter downstream by two or three times. Without a cyclone the filter element would quickly clog and then have to be replaced.