Vacuum Amplifier: Description and Operation

SYSTEM DESCRIPTION

PURPOSE
The EGR system is used to reduce Oxides of Nitrogen (NOx) emissions.

OPERATION
When the engine is under part-load, the EGR valve admits a small amount of exhaust gas into the air/fuel charge . The exhaust gas is essentially inert (contains no fuel or oxidizer) and reduces peak combustion temperatures and pressures by absorbing some of the heat of combustion without participating in the actual burn.

Fig. 26 Testing EGR Valve (California):

EGR VALVE
The EGR valve meters exhaust gas into the intake system. The EGR valve is normally closed. When the system is operating, ported vacuum is applied to the diaphragm chamber of the EGR valve, opening the valve during acceleration and cruising conditions.

Fig. 38 Vacuum Thermo-switch, 16V (California):

THERMO-VACUUM VALVE
The thermo-vacuum valve permits vacuum to the EGR valve only when the engine is at operating temperature.

Fig. 43 VACUUM AMPLIFIER:

VACUUM AMPLIFIER
The principal operation is based on utilization of venturi vacuum at the throttle housing. The venturi vacuum signal controls the vacuum amplifier which regulates the E.G.R. valve. This allows the correct amount of exhaust gas recirculation in relation to the intake air flow.

The vacuum amplifier receives two input vacuum signals (a weak venturi vacuum signal to be amplified and a strong manifold signal for its power source) to operate the E.G.R. valve.