The Automotive Vacuum System - Mityvac MI8000 Benutzerhandbuch

the automotive vacuum sYstem

This manual deals with vacuum and pressure, how
it is used in various automotive systems and how
the vacuum pump can be used to test and diagnose
these systems. This section discusses what vacuum
is, how it is measured, where it comes from on an
automobile, the system for distributing and using
vacuum, and some troubleshooting basics.
WHAT IS VACUUM?
Put simply, vacuum is empty space, and may exist
as either a total or partial vacuum. Vacuum does
not, of itself, create power. Rather, power for
vacuum devices depends on the presence of
atmospheric pressure. The atmosphere exerts a
pressure of 1bar (14.7 psi) on everything at sea
level. If a portion of the air is removed from one
side of a diaphragm (partial vacuum), the
atmospheric pressure will exert a force on the
diaphragm. The force is equal to the pressure
difference times the diaphragm area. Generally, the
less air (greater vacuum) in a given space, the more
the atmosphere tries to get in and the more force
is created.
Power Brake
Booster
FIGURE 2: TYPICAL VACUUM DISTRIBUTION SYSTEM
Form 824357
To Intake Manifold
Intake Air Motor
WHY ENGINES CREATE VACUUM
Vacuum is created when air is withdrawn from
a given volume, or a sealed volume is increased.
That is why vacuum is avail able in an engine.
On the intake stroke, the piston moves down, this
creates a partial vacuum because the volume of the
cylinder is increased. Air cannot rush through the
intake system fast enough to totally fill the space
created when the piston moves down (FIGURE 1).
This is the most common automotive vacuum
supply source.
GASOLINE VS. DIESEL VACUUM
Because a diesel engine does not produce as much
vacuum as a gasoline engine, a mechanical vacuum
pump must be employed to operate vacuum
devices. The pump is useful in testing devices
on both types of engines.
Intake Stroke
FIGURE 1: THE ENGINE AS A VACUUM SOURCE
VACUUM DISTRIBUTION BLOCK
Auto
Trans
To Speed
Control
Distributor
Advance
Vacuum Port
Air
Vacuum
To A/C
Heater
PRNDL Switch
Brake
Release Motor
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