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Fuel vapor leak detection system
This article describes a Differential flow sensing through respective flow path portions of a system for detecting leakage from an evaporative emission control system. a leak detection system that employs a differential flow sensing principle for detecting fuel vapor leakage from the evaporative emission system of a vehicle. The test involves a canister purge solenoid (CPS) valve , positively pressurizing that portion of the evaporative emission system which is upstream of the CPS valve relative to the engine. it less complicated, more economical and reliable, than prior systems not using the differential flow sensing principle. The differential pressure technique utilised here is immune to variations in ambient temperature, pressure, engine manifold vacuum, or supply voltage. So this has improved accuracy and for avoiding false readings that might otherwise arise on account of such variables. It can also cancel out the effects of three external variables by comparing the leakage flow with a known calibrated reference leakage. a canister vent valve is also not required. There is also physical integration of certain components of the leak detection system with a fuel vapor collection canister. This brings savings in terms of space which maybe important. Another advantage is that a fuel vapor leak detection test can be performed either when the engine is running or not running.

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