EVAP system in automobile.

Evaporative Emission Control System ( EVAP System)
EVAP system in automobiles
Charcoal Canister

Most of you would be unaware about EVAP systemEvap stands for " Evaporative Emission Control System”. The BS4 emission norms made it mandatory for vehicles to use EVAP systemsFor this the vehicles had to be installed with charcoal canisters. Earlier the fuel tanks of vehicles were provided with small holes to prevent the formation of vacuum. inside the fuel tank. When the fuel was supplied to to carburetor , the air used to rush inside to cover the space and hence the vacuum formation was prevented. The fuel vapour formed inside the tank used to escape to atmosphere through the same holes.

What is evaporative emission?

The fuels used in vehicles are very volatile. They use to form vapor even at normal temperature. These vapors than escape from the fuel tank through the ventilation hole and get mixed with air in environment. They are very harmful for environment and are a majore contributor in vehicle pollution.

EVAP system

EVAP system in automobiles





The evap system consists of a charcoal canister. This canister contains activated charcoal. The charcoal is in powdered form so as to have large surface area. The canister contains 4 pipes. One pipe is connected to fuel tank vent provided to remove fuel vapours. The pipe is provided with a roll over valve. The function of the roll over valve is to prevent the flow of liquid fuel to canister in case of accidents. The liquid fuel can degrade activated charcoal. The second pipe I s called purge pipe. The purge pipe connects the canister to the carburetor through a purge valve. The purge valve is a non return valve, which  allows the flow in only one direction i.e. from canister to carburetor. One more pipe called canister overflow pipe is provided to remove any liquid fuel present inside canister. It is also provided with a pipe called vent pipe which helps in air supply. At the time of inlet stroke the vacuum inside the intake manifold sucks the air through the purge pipe, which ultimately pulls the air through  vent pipe and the sucked air moves through charcoal inside the canister. While moving through the canister it carries the particles of fuel trapped in charcoal. This air is sucked inside carburator through the purge purge pipe. In this way the EVAP system prevents the evaporative emissions.


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