What is the part on your tractor that needs the most frequent maintenance? If you answered “clutch” or “brakes”, or “tyres” you would be wrong. For in South Africa’s dry, dusty operating environment it is the air filter.

Oil bath air filter

Older tractors are generally fitted with an oil-bath filter which comprises a vertical tube inside a tube of greater diameter. The bottom end of the inner tube is submerged into a reservoir of oil, and the space between the two tubes above the oil is filled with, essentially, steel wool as the filter “element”.

Oil bath air filter

Air is drawn into the engine down the inner tube and through the oil, then up through the steel wool element, which itself becomes coated with oil, maintains an oily stickiness, thus capturing dust particles as they pass through.

This ensures that clean, dust-free air enters the engine.

Air filter maintenance

Maintenance of such a filter entails washing the steel wool in a solvent such as petrol, to remove the old oil, and its load of dust.

At the same time, the oil storage bath should be washed out, dried and refilled.

Failure to wash the steel wool will result in it becoming coated in dust to the extent that it loses its filtering efficiency and in extreme cases can even result in air starvation to the engine.

Failure to clean the oil bath will result in a heavy, thick sludge of dust settling at the bottom, rendering the oil thicker, and less able to coat the steel wool element by capillary action.

Hygroscopic oil

Plus, although it is counter-intuitive, oil is slightly hygroscopic. In time it will absorb moisture from the atmosphere – moisture which, if drawn up into the steel wool by capillary action will result in the wool beginning to corrode, and which will evaporate into the air being drawn into the engine.

You will learn to recognise oil that has absorbed excessive moisture as it will turn opaque and, in extreme cases, milky white.

Finally, failure to ensure the oil reservoir has sufficient oil in it will result in the steel wool element drying out and losing its efficiency to attract and collect the dust particles.

Paper air filter element

Modern tractors have, of course, done away with all this oily paraphernalia and the filter comprises a housing into which is slipped a corrugated paper element.

Paper air filter element

The engine-bound air is able to pass through the porous paper but the dust particles are not. In time, therefore, the paper element becomes clogged with dust, losing efficiency and possibly leading to air starvation in the engine.

Compressed air

Although one can, as a stop-gap measure, blow most of the dust out of a used element using a jet of compressed air from inside the element it is much wiser to simply replace the element with a new one.

It goes without saying that the correct filter element must be used, and the housing correctly closed and secured as a gap between the element ends and the housing will result in uncleaned air bypassing the filter and entering the engine.

How often one shopuld clean the air filter or replace the element depends on the workload of the tractor and the degree of dust encountered in its working environment. Suffice to say, however, that one can’t overdo air filter maintenance in a dusty country such as South Africa.

Small machines

Although these principles apply to machines working in very dusty environment such as tractors, bulldozers and even farm bakkies, the same principle of ensuring a regular cleaning or replacement of the air filter applies just as well to lawnmowers, chainsaws and brushcutters.

Main image: Side view of  Ferguson TE20 showing the air filter under the bonnet, just in front of the steering wheel.


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