Ameer Randolph
Fuel tank vents are necessary to allow fuel to continue pumping without causing a vacuum. This can be achieved through the gas cap or a breather tube. The latter is usually routed higher than the tank and exits below it to prevent spillage or siphoning. When adding a fuel tank vent, it is important to ensure that the vent is mounted vertically to avoid it shutting off. For boats, fuel vent screens should be kept clean and dry to prevent water intrusion. Additionally, the type of gas cap is important, with vented caps being common due to the expansion of modern fuels.
| Characteristics | Values |
|---|---|
| Why vent a fuel tank? | To allow the fuel to continue to pump without causing a vacuum. |
| How to vent a fuel tank? | Through the gas cap, or via a breather tube. |
| Gas cap characteristics | Vented, locking-type, or vented-type. |
| Breather tube characteristics | Routed higher than the tank, exiting below it to prevent spillage or siphoning. |
| Fuel tank venting issues | Fuel becoming trapped in the line, causing pressure or vacuum issues. |
| Solutions to venting issues | Ensure the vent is mounted vertically, clean or replace clogged vents, avoid sags or traps in the vent line. |
| Boat fuel tank venting tips | Mount the vent high and angle it aft and slightly downward to prevent water intrusion, consider a clamshell cover. |
| Fuel tank venting in cars | Use a larger hose than the standard 5/16-inch line to properly vent the tank during filling. |
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What You'll Learn
Ensure the fuel tank vent is mounted vertically to avoid shut off
Ensuring that the fuel tank vent is mounted vertically is crucial to prevent the vent from shutting off. This is because, if the vent is mounted at an angle, it can shut off, defeating the purpose of the venting system. The purpose of a fuel tank vent is to allow the tank to breathe by relieving vacuum and pressure. Gasoline expands in volume as it warms up and shrinks as it cools down, and the fuel level in the tank changes throughout the day, even when the vehicle is stationary. Thus, the tank must be able to release pressure and maintain a vacuum to prevent explosions, ruptures, and spills.
The number one consideration when installing a fuel tank vent line is to ensure that the vent is mounted vertically. If the vent is mounted sideways or at an angle, it can shut off, causing the tank to build pressure or a vacuum. This can lead to gas and/or odour coming from the vent line, and in extreme cases, damage to the tank. Therefore, it is imperative to mount the vent vertically to avoid these issues.
The specific design of a fuel tank venting system depends on the size and type of tank, as well as the intended use of the vehicle. However, the fundamental principle of venting remains the same: to allow air to flow in and out of the tank, preventing the build-up of pressure or a vacuum. This is achieved by ensuring the vent is mounted vertically and higher than the highest point on the tank, including the fuel filler neck.
Additionally, it is important to ensure that the vent line does not have any dips or low spots where fuel or condensation can get trapped. This can also lead to pressure build-up and potential damage to the tank. By following these guidelines and ensuring the vent is mounted vertically, you can effectively avoid shut-off and maintain the proper functioning of the fuel tank venting system.
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Avoid trapping fuel in the vent line
To avoid trapping fuel in the vent line, it is important to understand the purpose of a fuel tank vent. Fuel tank vents are designed to let air in and out of the tank. When you fill up your tank, air needs to escape, and when fuel leaves the tank, air must enter to avoid creating a vacuum. This process is known as venting, and it is crucial for maintaining optimal fuel flow and preventing fuel tank explosions.
When installing a vent hose, it is essential to avoid sags or dips in the vent line. These sags or dips can trap fuel, preventing the vent system from functioning properly. The vent line should be installed as straight as possible, allowing any fuel to drain back into the tank via gravity. Additionally, ensure that the vent line is higher than the highest point on the tank, including the fuel filler neck. This prevents fuel or condensation from getting trapped in the line, which can lead to pressure or vacuum build-up and potential tank damage.
It is also important to regularly clean and service your fuel tank and vent line to prevent clogging and ensure efficient operation. Debris, condensation, and even insect nests can block the vent line, affecting the airflow and the overall performance of the fuel system. Therefore, it is recommended to use quality fuel and regularly inspect and clean the vent line and vent valve to maintain proper ventilation and prevent blockages.
Furthermore, consider using a fuel surge protector or a no-spill valve. These devices are installed in the vertical run of the vent line and prevent fuel from spewing out when filling the tank. They are environmentally friendly and help maintain a clean fuel system. Additionally, some vents on the market offer designs that help shed water, such as a 90-degree upward bend in the hose fitting, allowing water to drain back out.
By following these guidelines and maintaining a well-functioning fuel ventilation system, you can avoid trapping fuel in the vent line and ensure the smooth operation of your vehicle or boat.
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Keep the through-hull vent dry
Keeping a through-hull vent dry is crucial to prevent water intrusion, which can cause issues with your boat's fuel vent. Here are some ways to keep the through-hull vent dry:
Mount the Vent at a Suitable Height: Install the vent at a height that is not constantly exposed to spray or splashing water. By mounting it higher, you reduce the chances of water directly entering the vent.
Angle the Vent Opening: Position the vent opening aft and slightly downward. This angling shields the vent from oncoming waves, rain, and dew, preventing water intrusion while still allowing fumes to vent outboard.
Utilize a 90-Degree Upward Bend: Implement a 90-degree upward bend in the hose fitting. This bend creates an upward loop in the line, allowing any splashed or intruding water to drain back out, preventing it from reaching the fuel tank.
Choose a Water-Resistant Design: Opt for fuel vents with designs that aid in shedding water. For example, Perko's through-hull vent features an integral splash guard, while Attwood's 90-degree P-trap fuel tank vent includes a baffle chamber that traps and redirects errant water.
Cover the Fuel Vent: If your boat encounters heavy spray and you're experiencing issues with water in the fuel, consider using a clamshell cover over the fuel vent. This cover helps shield the vent from direct water exposure, reducing the chances of water intrusion.
By following these guidelines, you can effectively minimize the chances of water entering your through-hull vent, helping to keep it dry and maintaining the proper functioning of your boat's fuel venting system.
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Use a clamshell cover to protect the fuel vent
To ensure the fuel tank vent is protected, using a clamshell cover is a durable and attractive solution. Clamshell vent covers are designed to protect your boat's vents and route cables. They are usually made from marine-grade plastic and offer long-lasting resistance to UV rays, saltwater, and harsh weather.
Clamshell vent covers are available in different sizes and colours, such as white and black, to match your boat's aesthetic. They are designed to cover existing vents and shield thru-hull openings from water spray. These covers are an economical and attractive alternative to metal clamshells, providing maximum longevity with their super-strong moulded design.
When installing a clamshell cover, it is important to ensure the fuel vent is mounted vertically to prevent it from shutting off. The vent hose should also be installed correctly to avoid fuel puddles. Additionally, the vent should be mounted relatively high to protect it from water splashes.
By following these instructions and utilising a clamshell cover, you can effectively protect your fuel tank vent while enhancing the appearance of your boat.
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Understand the basic principles of fuel tank venting
Fuel tank vents are an essential safety feature in vehicles, allowing pressure to be released from the tank to prevent explosions, ruptures, or spills. The basic principle behind fuel tank venting is to allow air to flow in and out of the tank, maintaining a balance of pressure and vacuum inside. This is particularly important due to the nature of fuel, which expands and contracts with temperature changes, leading to changes in volume and pressure.
The venting system in a fuel tank helps to mitigate safety risks. Without proper venting, a vacuum can form inside the tank as fuel is consumed, potentially causing it to collapse or rupture. This was the case with several General Motors pickup trucks in the 1980s, which had fuel tanks located beneath the rear seats. The lack of proper venting led to incidents of tank rupture and leakage, posing a severe fire hazard. As a result, over 3 million trucks were recalled, and a redesign of the fuel tank venting system was implemented.
Fuel tank vents can be either unfiltered or filtered. Unfiltered vents are simple in design, allowing unrestricted airflow without filtration. They are typically used in low-contamination-risk environments or when the fuel has been treated to prevent contamination. Filtered vents, on the other hand, are designed to protect the fuel system from contaminants by capturing particles and other impurities in the airflow.
The size and type of fuel tank, along with the vehicle's intended use, determine the specific design of the venting system. For example, the standard 5/16-inch line used as a fuel tank vent may not be sufficient for proper ventilation during filling, as explained by Justin, the general manager at Tanks Inc. Modern fuels, with their alcohol and additive content, expand more than traditional fuels, further emphasizing the need for effective venting.
Additionally, the orientation of the vent is crucial. It is recommended to mount the vent vertically to ensure proper functionality. Angled vents may shut off, disrupting the airflow and compromising the venting system's effectiveness.
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Frequently asked questions
Some tips include:
- Using a vented gas cap to allow air to enter and exit the tank
- Ensuring the vent line is straight to allow fuel to drain back into the tank
- Mounting the vent vertically to prevent it from shutting off
- Keeping the through-hull vent dry to prevent water intrusion
- Covering the fuel vent with a clamshell cover to prevent water intrusion.
Some common issues with fuel tank vents include:
- The vent hose being blocked, causing fuel to become trapped in the line
- The vent not being mounted high enough, allowing water intrusion
- The vent not being Coast Guard approved
- The gas cap not being vented, causing issues with vapour pressure.
Some products that can be used to add a fuel tank vent include:
- Perko’s through-hull vent, which includes an integral splash guard
- Attwood’s 90-degree P-trap fuel tank vent, which features a baffle chamber to trap water
- Eddie Motorsports' stainless steel marine vents, which can accommodate a thick hull and be bolted through sheet metal
- Aeromotive's 6.2-gallon aluminium fuel tank, which has two AN-8 vents with rollover valves.
