|
|
| |
Engines run on a vacuum system. A vacuum exists in an area where the
pressure is lower than the atmosphere outside of it. Reducing the
pressure inside of something causes suction. For example, when you
drink soda through a straw, the atmospheric pressure in the air
pushes down on your soda and pushes it up into your mouth. The same
principal applies to your engine. When the piston travels down in the
cylinder it lowers the atmospheric pressure in the cylinder and forms
a vacuum. This vacuum is used to draw in the air and fuel mixture for
combustion. The vacuum created in your engine not only pulls the fuel
into the combustion chamber, it also serves many other functions. The
running engine causes the carburetor and the intake manifold to
produce "vacuum power," which is harnessed for the operation of
several other devices.
Vacuum is used in the ignition-distributor vacuum-advance mechanism.
At part throttle, the vacuum causes the spark to give thinner
mixtures more time to burn.
The positive crankcase ventilating system (PCV) uses the vacuum to
remove vapor and exhaust gases from the crankcase.
The vapor recovery system uses the vacuum to trap fuel from the
carburetor float bowl and fuel tank in a canister. Starting the
engine causes the vacuum port in the canister to pull fresh air into
the canister to clean out the trapped fuel vapor.
Vacuum from the intake manifold creates the heated air system that
helps to warm up your carburetor when it's cold.
The EGR valve (exhaust-gas recirculation system) works, because of
vacuum, to reduce pollutants produced by the engine.
Many air conditioning systems use the vacuum from the intake manifold
to open and close air-conditioner doors to produce the heated air and
cooled air required inside your vehicle.
Intake manifold vacuum also is used for the braking effort in power
brakes. When you push the brake pedal down, a valve lets the vacuum
into one section of the power-brake unit. The atmospheric pressure
moves a piston or diaphragm to provide the braking action.
|
|
|
|
|
