Evaporative Emissions System: Description and Operation

Evaporative Control System (ECS):

SYSTEM DESCRIPTION

The Evaporative Control System consists of the fuel tank and filler cap, a two-way valve, a check/relief valve, two roll-over/float valves, a vapor separator tank, and a charcoal canister with integral purge control valve. The system collects fuel vapors, that would otherwise be discharged into the atmosphere, and condenses them in a charcoal canister where they are temporarily stored. When the engine is started, the stored fuel and vapors are atomized with fresh air and directed to the intake to be burned in the engine. This system of vapor recovery helps not only to prevent raw hydrocarbon emissions, but also promotes fuel economy by eliminating fuel loss through evaporation.

Charcoal Canister:

CHARCOAL CANISTER

The charcoal canister is filled with activated charcoal, to condense and store fuel vapors as they enter the canister. The charcoal separates fuel vapors from air, allowing air to escape through the vent while containing the hydrocarbons. It has a valve built onto it to control purging of the fuel vapors. When the engine is not running, the diaphragm spring holds the valve closed, preventing fuel vapor from escaping through the intake system and air cleaner. When the engine is running, throttle valve port vacuum is applied to the diaphragm of the purge control valve. When sufficient vacuum is present (indicating the engine is operating under load at a minimum rpm) the purge control valve opens and fuel vapors released from the charcoal (mixed with fresh air) are drawn into the intake and burned along with the normal air/fuel charge.

Check/Relief Valve:

CHECK/RELIEF VALVE

The check/relief valve is installed in-line to the charcoal canister. When the tank vapor pressure exceeds a specified level, the valve opens to relieve the excess pressure and let the vapors into the charcoal canister. When the vapor pressure in the tank is less than atmospheric by a specific value the valve allows ambient air from the canister to enter the tank to restore pressure equilibrium. Stated simply, the valve will open in either direction when the pressure differential is great enough. A slightly greater differential is required to relieve pressure within the tank, than is required to equalize lower than ambient pressures.

Fuel Tank And Vapor Separator Tank:

FUEL TANK AND FILLER CAP

The fuel tank incorporates vents at the top with special valves to prevent liquid fuel from leaking through the evaporative system in case of overfilling or in the event the vehicle is rolled over in an accident. Unlike most models, the Impulse fuel tank uses a sealed filler cap.

Rollover/Float Valve:

ROLL-OVER/FLOAT VALVE

The rollover/float valves are designed to prevent fuel from leaking through the evaporative system in the event the vehicle has turned over in an accident. They also prevent fuel from saturating the evaporative system with liquid fuel in case the tank is over filled.

Vapor Separator Tank:

VAPOR SEPARATOR TANK

The vapor separator tank is used to condense excess fuel vapors and separate vapors from liquid fuel. The liquid fuel is drained back into the fuel tank while the vapors are sent to the charcoal canister for storage.