Snow Part 02: Ejective Precleaners – The Prescreen

Integrated permanent prescreens clog quickly and ice over with wet driving snow, choking off air flow to the engine. (Turbo II, Turbo III, O’Cautro, Klean Air)

Series 9000 Removable Prescreen

Series 9000 Removable Prescreen

Air enters the underside of the dome through SCREENED LOUVERS (shown in GREEN), which prevents clogging by blocking any particles larger than the ejection slot from entering the unit. In snowy weather, the prescreen is dropped down the air inlet pipe to eliminate the possibility of the prescreen blinding over with snow or ice.

Prescreens are incorporated into many of the precleaner designs. Not all precleaners, however, have prescreens.

  • There are many manufacturers that have copied the original Turbo I and Turbo II designs with integrated prescreens built into the top of the precleaner that cannot be removed.
  • The Sy-Klone Series 9000 has a removable prescreen that is dropped down the air inlet pipe in snow applications, then put back into position after the spring thaw.

The prescreen is designed to stop objects larger than can be ejected from entering the precleaner. The theory is that anything that enters the precleaner that cannot be immediately ejected will cause one or more of these problems:

  • It will stop the precleaner from working by jamming or clogging
  • Break an internal component of the precleaner
  • Pass through to the air filter housing.

In snow there are several serious problems associated with prescreens:

  • Metal prescreens are often chilled below 32°F (the temperature of the snow) which causes the snowflakes to stick and freeze to the metal prescreen. This can blind over the prescreen, so less and less air can pass through.
  • The prescreen is designed to allow dirt particles to pass through at a high rate of speed. High humidity large flake snow will not rapidly pass through the screen but instead will splat onto the surface of the prescreen, allowing a layer of frozen snow or ice to accumulate on the prescreen.
  • In low humidity snow when the snow is very fine the precleaner does a better job, as the fine dry snow reacts much like small dirt particles.

Due to the constantly changing environments which produce snow and ice, an operator has no way of knowing whether the snow will be wet or relatively dry so the precleaner must perform well in both conditions.

Given the known perils of choking off the intake system with a blinded over prescreen, using a precleaner with a non-removable fixed prescreen is not advised in a snow application.

Next: Snow Part 3: Stratification of Debris Fields

Previous: Part 1: Intro – The Problem with Snow Previous

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