Snow Part 08: Ingestive Precleaners: Tube Body / Dona Cone

Tube Body precleaners contain very tight tolerances which are quickly filled by snow, and by design, are not suitable for snow applications.This system relies upon a particle separation process which takes place in very small diameter.

How a tube body precleaner works:

  • Tubes draw air through a very small orifice, which accelerates the air.
  • The air passes through louvers which spin the air in the tube creating a centrifugal separation process. The tolerances in these tube bodies are very small.
  • At the bottom of the tube, there is a small gap around the edges for debris (which is theoretically riding around the sides of the tubes) can fall out.
  • Debris is either removed by a scavenger connection to the machine’s exhaust system, or it collects within the housing and needs to be emptied.
  • In the center of the bottom of the tube, inside the gap where debris falls through, there is a small cone-shaped air inlet that is pulling air from the center of the tube’s airspace.

Dry snow is drawn into the tube bodies, going through the centrifugal separation process, but because of its low mass, much of the dry snow is left floating in the center of the tube, where it is drawn straight down the cone-shaped air intake, which is in the middle of the tube body. The result is that the snow is drawn down onto the filter.

Wet snow is much heavier and so more affected by the centrifugal separation process. However, its heavy mass causes the snow to accumulate around the bottom of the tube between the bottom of the cone-shaped inlet and the sides of the tube. Because the tolerances at this point are very small, it takes very little snow accumulation before all of the snow is trapped in the tube and by necessity drawn down the cone-shaped inlet tube onto the filter.

There are several configurations of Tube Bodies:

The most popular involves the removal of the separated debris by a vacuum tube which gets its vacuum from the machines exhaust pipe. By attaching the scavenger tube to the exhaust pipe it creates a venturi effect which gives the tube suction. The suction end of the tube is plugged into the Tube Body housing and is used to vacuum out the debris that falls out of the bottom of the tubes.

This suction is very effective on dry debris but is ineffectual on water. The hot exhaust gases which come from the Scavenger tube heat the tube body assembly and cause the trapped snow to melt. This creates water which is difficult to vacuum out of the tube body housing. The accumulation of heat and water in the tube body accelerates the process of dampening the filter, which can then freeze over and starve the engine of needed air.

The Dona Cone does not use the scavenger system but rather relies upon gravity for the snow to fall within the precleaner housing from the back of the tubes into a collection area within the Tube body housing.  If working properly this system needs to be dumped on a regular basis. This can become a significant safety problem at very low temperatures in hostile conditions when getting out of the cab to work is nearly impossible. This system has all of the design problems associated with the tube bodies without the benefit of a built-in scavenger system.

Both systems are designed for low humidity and fine dust. No matter how dry the air becomes, the snow melts into water when heated up inside the precleaner.  This system by design is not suitable for snow applications.

The Series 9000 contains no small spaces which can clog, and snow is not accumulated within the precleaner.

Next: Part 9–Dust Bowls

Previous: Part 7–Tangential air filter housings

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