Aprilia SR 50 servicemanual - Scootergrisen
Aprilia SR 50 servicemanual - Scootergrisen
Aprilia SR 50 servicemanual - Scootergrisen
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<strong>SR</strong> <strong>50</strong><br />
SAS<br />
The Secondary Air System (SAS) has been developed to<br />
reduce carbon oxide and unburnt hydrocarbon emissions in<br />
vehicles that are not equipped with a lambda sensor. Natural<br />
air (which is rich in oxygen) is channelled into the exhaust<br />
stream to trigger a post-combustion process that raises the<br />
temperature of the exhaust gasses for a quick light-off of the<br />
catalyst.<br />
The secondary air system is especially useful when the<br />
engine is idling and during warm-up, since the catalyst alone<br />
is not capable of triggering post-combustion under these<br />
operating conditions.<br />
DESCRIPTION OF THE SYSTEM<br />
The secondary air system operates on pressure fluctuation<br />
in the exhaust system. During depression stages, the<br />
exhaust takes in oxygen-rich air from the secondary air<br />
system so unburnt gasses in the exhaust stream can<br />
complete the combustion.<br />
During overpressure stages, the secondary air reed valve<br />
cuts air supply to prevent backflow.<br />
On 4-stroke engines, the reed valve is equipped with a cutoff<br />
device that shuts down additional air during cut-off<br />
stages, as exceedingly lean exhaust gasses would lead to<br />
exhaust blowing, resulting in exhaust valve and catalytic<br />
converter damage.<br />
DETAILS OF SAS<br />
• The system consists of a rubber hose that takes filtered<br />
air in through a scoop on the casing.<br />
• Secondary air flow is controlled by a reed check valve,<br />
on the vehicle right-hand side, on the flywheel cover.<br />
• The secondary air tube is connected to a flanged metal<br />
fitting attached directly to the head exhaust duct.<br />
ENGINE<br />
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