Diesel School – Wet type air filter

The wet type air filter is also known as an oil bath air cleaner. Air enters the filter at the top and flows down toward a bath of oil. The airflow then reverses direction and moves up through the filter element and onward to the engine. Heavier dust particles are separated from the air as the air passes over the oil bath. As the air suddenly changes its direction of movement from down to up, the heavier dust particles continue to move down (with gravity and inertia helping) and are then trapped in the oil. More sophisticated oil-bath filters have a secondary stage consisting of a metal-gauze or a paper filter element. As the airflow reverses its direction above the oil reservoir, it picks up an oil mist from the oil bath to keep the filter element soaked.

Oil bath filters were popular in older designs of tractors which spent much of their life in dusty environments. The oil in the bath was typically the same grade of engine oil which the tractor used and it allowed tractor operators to filter a lot of dust, and clean the filter without replacing any parts. In very dusty environments, Massey Ferguson recommended changing the oil in the bath every 8 hours of use. Perkins engines, which were really designed for Massey Ferguson tractors and Caterpillar machinery often have wet-type oil filters.

A Perkins wet-type air cleaner is shown in the diagram below. The wet type air cleaner must be drained at a suitable interval. The container and element (1) must be cleaned with kerosene or with another suitable fluid. Do not use gasoline. Check that the seal (3) is not damaged and renew it, if necessary. Fill to the indicated level (2) with clean engine lubricating oil.

Perkins Diesel Engine Wet-type air filter