Air supplied to an engine must be free from dirt and dust as far as possible. If there is any dirt in the entering air, it will act as an abrasive. Hence, abrasive wear there is will occur on pistons, rings, cylinder walls, valves, bearings and other relative moving parts. Under extreme conditions, the wear may become very much greater. An air filter also called air cleaner is always installed at the entrance of the inlet manifold.

1. AIR FILTER

2. AIR FILTER
Air supplied to an engine must be free from dirt and dust as far as
possible.
If there is any dirt in the entering air, it will act as an abrasive. Hence,
abrasive wear there is will occur on pistons, rings, cylinder walls, valves,
bearings and other relative moving parts.
Under extreme conditions, the wear may become very much greater.
An air filter also called air cleaner is always installed at the entrance of
the inlet manifold.

3. Air filter screens and filters air before it enters the engine cylinder.
This reduces wear of the engine components, formation of
deposits and sludge, and maintenance costs.
Air filter also captures moisture and carbon soot that are present in
the atmosphere in any trucking operation (in the case of engines
fitted to vehicles).
Air filter also acts as a silencer and reduces the noise of the air
rushing into the inlet manifold.

4. Air filter requirements
The following are the main requirements which an air filter must
fulfill:
1. Small resistance to the passage of air.
2. High efficiency or dust removing capacity.
3. Ease of cleaning the filter element.
4. Ability to operate without constant attention or excessively
frequent cleaning intervals.
5. Compact in size.
6. Moderate first cost.
7. Low operating expense, if any.

5. Types of air filters
Air filters are classified based on the following:
1. Principle of operation adopted.
2. Nature of the filtering material used.
The different types of air filters in common use are as follows:
1. Oil wetted mesh filter.
2. Oil bath filter.
3. Paper element filter.
4. Polyurethane filter.
The type of filter used in an engine depends on the condition of the
atmosphere in which the engine has to operate.

6. Oil wetted wire mesh filter
• This filter contains wire mesh coated with an oil film. The oil
film catches dust, particles in the air as the air flows through the
filter element. Clean air leaves the filter. This type of filter gives
adequate filtration where dust concentration is low.
• The filter element should be cleaned periodically, by washing it
with petrol or paraffin. After drying, the wire mesh is coated with
engine oil. Excess oil must be drained before refitting the
element.

8. Oil bath filter
•In this filter, filtration of dust particles takes place in two stages:
1. Air flows from top to bottom and then from bottom to top. The
reversal of air flow occurs at the oil surface and this causes the dust
particles to impinge on the surface of the oil and stick to it.
2. The partially clean oil laden air passes up into the steel wire mesh
element. Here the oil film on the element surface retains dust.
• Oil bath filter is an efficient one.
• The element and the oil bath should be washed periodically in paraffin
or petrol and dried. The oil container should be refilled with clean
engine oil upto the correct level.

10. Paper element filter
• In this filter, the resin impregnated paper element is in a pleated
form. This provides a large filtering surface. This filter has greater
efficiency and is compact.
• The primary disadvantage or the dry paper filter is its possible
damage during cleaning which may allow dirt to enter the engine.
• Soot particles from exhaust smoke also rapidly plug the paper filter.
Entry of soot particles can be eliminated by the proper placement of
the inlet air intake.
• Most vehicle engines now use dry filters because of their high
efficiency (99.9%). The filter element has to be replaced when the
dust accumulation on it is more.

12. Centrifugal air filter
• This type of filter is usually fitted as the first stage air cleaner on
engines operating in heavy dust concentrated locations.
• In this filter, a whirling motion is imparted to the dirty air on its
entry into the air cleaner.
• This causes the heavy dusty particles to be thrown out by the
centrifugal force, to the periphery of the casing.
• The casing has slots. Through these slots, the dust particles leave
out.

14. • The partially filtered air now passes through the vanes set at an
angle. These vanes correct the air flow to a straight direction.
• The air then enters into the main air filter. This precleaner removes a
large portion (70 to 80%) of the dust before it reaches the air filter.
• Most dry type air cleaner manufacturers classify their products as
normal duty, medium duty and heavy duty. The classification really
refers to the dust holding capacity at the time when maximum
allowable pressure restriction is reached for a dirty air filter.

15. • Normal duty air cleaners are suitable for most highway
vehicles.
• Medium duty air cleaners are suitable for areas where
dust concentration is low but greater dust holding
capacity is needed.
• Heavy duty cleaners are usually used in dusty and off
highway environments or applications where extremely
long time intervals are needed between servicing.