PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 1/TASK 2
(2) Directing the engine coolant, which is laden with engine heat,
a. Purpose. The air filter fits over the engine air intake to filter
out particles of foreign matter. Any foreign matter that enters the intake
will act as an abrasive between the cylinder walls and the pistons, greatly
shortening engine life. Two types of filters in use are the wet the and dry
The wet-type, or oil bath air filter, consists of the
main body, the filter element that is made of woven copper gauze, and the
cover. Operation is as follows: The incoming air enters between the cover
and the main body. It is pulled down to the bottom of the main body, where
it must make a 180 turn as it passes over the oil reservoir. As the air
passes over the oil reservoir, most of the particles will not make the turn;
they will hit the oil and be trapped.
As the air continues upward and
passes through the filter element, smaller particles that bypassed the oil
will be trapped.
The air keeps the filter element soaked with oil by
creating a fine spray as it passes the reservoir.
The air finally makes
another 180 turn and enters the carburetor.
c. Dry-Type (figure 9 on the following page). The dry-type air filter
passes the incoming air through a filtering medium before it enters the
The filtering medium consists of oil-soaked copper mesh or
replaceable pleated paper, the latter being the most common.
Principles of Carburetion
Air is composed of various gases, mostly
nitrogen and oxygen (78 percent nitrogen and 21 percent oxygen by volume).
These gases are composed of tiny particles called molecules as are all
In the air surrounding the earth, the molecules are able to
move quite freely in relation to each other as in all gases. The molecules
of air are attracted to the earth by gravity, creating the atmosphere. The
weight of the air molecules creates atmospheric pressure.