Rajan Wilcox
The fuel tank vent system, also known as the Evaporative Emissions Control system (EEC), is a nearly-universal emissions control system that has been mandated in all US market gasoline automobiles since the mid-1970s. It is designed to prevent gasoline evaporation, which can account for up to 20% of total harmful vehicle emissions if left uncontrolled. The EEC, commonly referred to as the charcoal canister, is a simple and passive system that requires little to no maintenance. It works by allowing atmospheric air to flow through the charcoal canister and into the fuel tank, preventing a vacuum from building up. The charcoal canister traps fuel vapors, helping to eliminate fuel odors and prevent overflow.
| Characteristics | Values |
|---|---|
| Purpose | To control emissions due to gasoline evaporation, which can account for up to 20% of total harmful vehicle emissions if not controlled. |
| Function | Allow atmospheric air to flow passively from the outside through the charcoal canister and expansion tanks and into the fuel tank to prevent any kind of vacuum from building up in the tank. |
| Maintenance | Requires no regular maintenance other than occasional checks to ensure lines are intact and the vent lines and carbon canister can breathe. |
| Performance | Costs nothing in performance or efficiency. |
| Efficiency | Costs nothing in performance or efficiency. |
| Composition | Contains activated carbon, which attracts and absorbs many kinds of molecules. |
| Installation | Installed at the end of the vent network, which is the only way for air and gases to enter or leave the system. |
| Usage | Used in the Evaporative Emissions Control system (EEC) since the mid-1970s. |
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What You'll Learn
The Evaporative Emissions Control system (EEC)
Prior to the EEC system, certain cars received air pumps that injected air into the exhaust to "clean up" the exhaust by diluting burnt fumes with fresh air. The EEC system works differently by collecting fuel vapours and redirecting them into a charcoal canister, which is then routed to the intake to allow the fumes to be burnt in the engine when it is running.
The fuel tank filler caps used on cars with EEC systems differ from those on cars without EEC. Most caps in the EEC system have built-in pressure-vacuum relief to prevent a vacuum lock due to fuel expansion or contraction. Some Ford-built cars use a combination valve that isolates the fuel tank from engine pressures and allows vapour to escape from the vapour separator tank to the vapour storage canister.
The EEC system is not necessary for the function of a car, but it is required in certain states or countries that have SMOG regulations. Some people choose to remove the EEC system to clean up the engine compartment and reduce the chances of vacuum leaks. However, if you are aiming for a high-point restoration, you may want to ensure you have the full EEC installed.
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Activated carbon
The activated charcoal canister, also known as the carbon canister, is an essential component of a vehicle's fuel tank vent system. Its primary function is to capture and store fuel vapours that evaporate from the fuel tank, preventing their release into the atmosphere. This system is designed to comply with legal regulations regarding vehicle emissions.
The canister is connected to the tank's bleeder or breather line via a pressure compensation line, allowing it to collect the volatile hydrocarbons that escape from the fuel as vapours under the influence of heat. These vapours are then stored within the canister, which contains activated charcoal or carbon, a highly porous material with a large surface area that effectively absorbs and retains the fuel vapours.
By capturing these vapours, the activated charcoal canister helps to maintain the slight vacuum within the fuel tank, preventing it from going flat. Additionally, the stored vapours are not wasted; the engine computer periodically opens the valving to the canister, allowing the engine to consume the trapped gasoline fumes. This process ensures that the vapours are utilized for combustion rather than being released as pollutants.
It is crucial to note that the carbon canister is designed to handle gasoline fumes and not liquid gasoline. Overfilling the fuel tank can cause liquid gasoline to enter the canister, damaging it beyond repair. Therefore, it is essential to exercise caution during refuelling to avoid overfilling and subsequently protect the integrity of the activated charcoal canister.
Activated charcoal canisters require regular maintenance and inspections to ensure their effectiveness and longevity. It is important to periodically check the canister for any damage, including inspecting the hoses, lines, connections, and the timed valve for any signs of wear or malfunction. By proactively maintaining the activated charcoal canister, vehicle owners can help protect the environment, comply with legal regulations, and maintain the overall performance of their vehicles.
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Homemade vapor canisters
A vapor canister is a component of a vehicle's fuel system that traps fuel vapours to reduce emissions. The vapours from the gas tank are stored in charcoal, which can, over time, become saturated and require replacement.
Another user on the Factory Five Racing Forum details their process of constructing a homemade vapor canister for their fuel tank vent. They used a stainless steel drinking bottle, a bulkhead adapter, activated charcoal, and fine steel wool, costing around $25. The user secured a 3/8" barb fitting into the bulkhead adapter, with approximately 3 inches of tightly packed steel wool on each end and about 4 ounces of activated charcoal in between. The user also notes that the canister can be serviced by removing the cotter pin and replacing the steel wool and activated charcoal.
A user on the Grassroots Motorsports forum seeks advice on constructing a homebrew system for their Fiat X1/9, which is being converted to standalone EFI. They are looking for advice on the control scheme for when to open the purge solenoid and suggestions for easily retrofit components, specifically a good purge valve.
It is important to note that while homemade vapor canisters may be constructed, it is always recommended to consult a professional mechanic for guidance and ensure that any modifications comply with local regulations and safety standards.
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Fuel tank design
Materials
The choice of material for a fuel tank is crucial as it ensures the tank's durability, resistance to corrosion, and ease of welding. Common materials used for fuel tanks include aluminum, stainless steel, high-carbon steel, fiberglass, plastic, and mild steel. Each material has its own advantages and disadvantages. For example, aluminum is lightweight, strong, and corrosion-resistant, while mild steel is more susceptible to corrosion and requires additional coating. Stainless steel is highly durable and resistant to corrosion but can be more expensive.
Ventilation and Vapor Control
Proper ventilation is essential in fuel tank design to prevent the buildup of fumes and to allow for the safe release of vapors. This can be achieved through the use of vent lines and vapor canisters, which may contain activated charcoal to absorb and filter fuel vapors. The positioning of the vapor canister is important, and it should be placed higher than the tank and preferably close to the filler pipe.
Inspection Ports
Including inspection ports in the fuel tank design allows for access to the interior of the tank for cleaning and maintenance. While some may consider these optional, they are crucial for proper maintenance, especially for diesel fuel tanks which are inherently sediment-laden and support microbial growth. The addition of inspection ports during the construction can increase costs, but retrofitting them to an existing tank can be even more expensive.
Safety Features
Fuel tanks should incorporate safety features to prevent fuel leakage and spills. This can include the use of gravity-activated rollover valves, fill plates with one-way valves, and anti-tip-over valves. Bladder-based tanks are also advantageous as they can be easily drained and cleaned.
Regulations and Standards
When designing a fuel tank, it is important to adhere to relevant regulations and standards, such as those outlined by the American Boat & Yacht Council (ABYC). These guidelines cover various aspects of fuel tank design, installation, and associated equipment to ensure safety and environmental compliance.
In summary, fuel tank design requires careful consideration of materials, ventilation, safety features, and adherence to regulations. By incorporating these aspects into the design, a safe, efficient, and reliable fuel storage and transportation system can be achieved.
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Charcoal canisters vs. extended vent lines
Charcoal canisters and extended vent lines are two solutions to the problem of fuel odours. Fuel odours can be caused by fuel vapours escaping from the fuel tank vent. This is particularly noticeable when a car has been locked in a garage for a long period, or in hot weather.
Some people opt to extend the vent line to move the overflow away from the car. However, this does not always eliminate the smell, especially during or after spirited driving or when the tank is filled to the neck. The vent line can also be coiled and extended downwards, but this does not address the issue of vapours escaping.
Charcoal canisters, on the other hand, are designed to absorb fuel vapours and reduce their escape into the atmosphere. They can be installed in the vent line to absorb vapours as air flows out of the tank. This is a more effective solution to the problem of fuel odours, and also helps to address the issue of vapours escaping. The charcoal can be replaced periodically. However, one potential drawback is that charcoal canisters take up more space than extended vent lines.
In some cases, a combination of the two solutions may be used. For example, a charcoal canister could be installed near the back of the car, above the transmission, with a vent line running to the back of the car. This provides the benefits of the charcoal canister while also allowing for more space.
It is worth noting that, in some jurisdictions, the use of charcoal canisters may be required by environmental regulations, such as those set by the EPA in the United States. These regulations aim to reduce diurnal emissions from fuel tanks, and charcoal canisters are an effective way to comply with these requirements.
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Frequently asked questions
The Evaporative Emissions Control system (EEC), or charcoal canister, is an emissions control system that has been mandated on every US market gasoline automobile since the mid-1970s. It works by trapping fuel vapors using a specialized charcoal media blend, keeping your garage or cabin free of unwanted fumes.
The fuel tank has a closed venting network. The fuel filler cap is sealed, so the vent network is the only way air and gases can enter or leave the system. Gasoline evaporates and consists of a variety of light hydrocarbon molecules. The canister contains activated carbon, which attracts and absorbs these molecules.
Emissions due to gasoline evaporation can account for up to 20% of total harmful vehicle emissions if not controlled. The charcoal canister is a mostly passive system that requires no regular maintenance other than occasional checks to ensure lines are intact and the vent lines and carbon canisters can breathe.
