« Back to Dictionary Index
An “anti-percolation valve” is used in older carburetor systems, apart of evaporative emissions control. Here’s a breakdown of its function and purpose:
- Function: The anti-percolation valve is designed to manage vapors that may form within the carburetor’s main discharge tube or well, especially when the engine is hot and turned off (a condition known as percolation).
- Preventing Fuel Evaporation: After engine shutdown, heat can cause fuel in the carburetor to vaporize, leading to increased emissions and potential starting issues. The anti-percolation valve helps by venting these vapors away from the carburetor.
- Evaporative Emissions Control: Instead of releasing these vapors directly into the atmosphere, which contributes to air pollution, the anti-percolation valve routes them into an evaporative emission canister (commonly known as a charcoal canister).
- Storage and Recycling: In the evaporative emission canister, the vapors are stored temporarily. When the vehicle is restarted, the engine’s intake manifold draws these stored vapors back into the combustion chamber to be burned along with the fuel mixture. This process helps achieve a richer air-fuel mixture during engine startup, aiding in smoother and more efficient ignition.
- Regulation: The function of the anti-percolation valve is crucial for complying with emissions regulations, which aim to reduce harmful emissions from vehicles.
- Modern Applications: In modern vehicles, carburetors have largely been replaced by fuel injection systems, and evaporative emissions control is managed by sophisticated systems that include vapor recovery and emission controls integrated with the engine management system.
In summary, the anti-percolation valve in a carburetor system helps manage vapors to reduce emissions and improve starting performance by rerouting vapors into an evaporative emission canister for storage and subsequent recycling into the engine intake system.
See
- Percolation