… this saying always springs to mind when I think about the early dust tests carried out for one of our major clients, a project for which I provided technical support when I was working in this field. Like all vehicle manufacturers, this client required their vehicles to be suitable for use in all countries. This was, of course, a big challenge, particularly in the 1960s. At that time, one aspect of our work was cleaning intake air in some of the more dusty corners of the globe.
As early as the mid-1960s, my client wanted to extend the maintenance intervals for the oil-bath air filters they were using at the time in their minibuses and flatbed trucks. And in the 1970s, after the oil-bath air filters had been replaced with paper air filters, the topic was on the agenda once more. The reason for this was simple: with the switch to the paper insert, the level of efficiency, i.e. dust filtration efficiency, improved significantly. However, as paper filters provided lower capacity than oil-bath air filters, the overall dust holding was reduced at the same time. For this reason, solutions had to be specially developed for dusty countries like those in Africa or South America, in order to redress this imbalance.
We here at MANN+HUMMEL were also in demand as a development partner and carried out numerous tests in the laboratory with maintenance-free pre-separators, which discharged the dust collected into the air. Depending on the configurations, the filter service life was quickly extended by two to two-and-a-half times. Starting in 1974, various tests were then carried out in Southern Algeria with the aim of checking the mode of operation of these cyclone separators. Contrary to expectation, however, the result after two days of tests was rather discouraging: with or without the cyclone, the dust incidence in the air filter was almost the same. But how could that be?
We examined, considered and eventually determined the following: these models used rear-mounted engines, which primarily would have sucked in the dust stirred up by the front wheels, so the inlet opening for the air intake was moved to the front of the vehicle. These then led to the engine via long ducts laid on the underbody. It was these long air ducts which brought about a large reduction in the air pulsation and thus the air pressure. This is something we had not considered in the laboratory tests. Small cause, big impact: The drop-in pressure meant that the cyclones were able to draw external air to their outlet, which significantly impaired their function in that the automatic emptying of the dust via the dust separation valve did not work.
We therefore decided to attach dust pots to the cyclone’s outlets, which were intended to close off the system and thus improve the pressure ratios. We built the prototypes directly on site using a couple of drinks cans, attached them and what can I say? Things improved immediately. At the end of the testing programme, we even achieved the target result – a satisfactory conclusion for our client too. There was, however, one drawback to our solution that we were not able to resolve: there was still an element of maintenance involved, i.e. emptying the dust pot. As soon as the dust pot was full, the separating function was once again reduced to nil.
In the years that followed, many more versions would be developed for our major clients and put to use in dusty countries. Before announcing any potential optimisations however, we always made sure that our ideas would work by way of on-site tests. After all, not all laboratory tests can be usefully implemented in practice and ‘learning by doing’ still has an important role to play, even in these times of high-tech laboratory facilities.