What is the purpose of a fuel tank?

Fuel tanks are an integral part of any vehicle, serving as a storage container for the fuel that powers the engine. However, fuel tanks can also pose a safety risk if not properly designed and maintained. One important feature of fuel tanks that helps to mitigate these risks is a venting system. In this article, we will explore the reasons why fuel tanks need to be vented, the dangers of unvented tanks, and the different types of vents that are used. By understanding the role of fuel tank vents, we can better appreciate the importance of proper design and maintenance in ensuring the safety of vehicles and their passengers.

The dangers of unvented fuel tanks

Unvented fuel tanks can pose a serious risk to the safety of a vehicle and its passengers. One of the main dangers of unvented tanks is the risk of deformity or tank rupture. As fuel is consumed from the tank, a vacuum is created which can cause the tank to collapse. This can lead to damage to the tank itself and potentially even cause a fuel leak. In addition, if the tank is not properly vented, pressure can build up inside the tank as the fuel expands due to changes in temperature. This can cause the tank to rupture, posing a serious hazard to the vehicle and anyone nearby.

When Tank Aren’t vented Properly

One example of a time when a fuel tank was not properly vented occurred in the 1980s, when several General Motors pickup trucks were recalled due to a defect in the fuel tank design. The trucks in question had fuel tanks that were in the cab of the vehicle, beneath the rear seats. These tanks were not properly vented, which resulted in a few incidents where the tanks ruptured or leaked, posing a serious fire hazard. In response to this issue, General Motors recalled over 3 million pickup trucks and implemented a design change to the fuel tank venting system to prevent future incidents. This incident highlights the importance of proper fuel tank venting in ensuring the safety of vehicles and their passengers.

The role of vents in fuel tank safety

Fuel tank vents are designed to prevent the dangers associated with unvented tanks. They allow pressure to be released from the tank, preventing the risk of explosion or rupture. In addition, vents can help to prevent fuel spills or leaks by maintaining a certain level of vacuum in the tank. This can help to prevent fuel from being forced out of the tank due to changes in pressure or temperature. In this way, fuel tank vents play a crucial role in ensuring the safety of vehicles and their passengers.

It’s important to note that fuel tanks can be vented in a variety of ways, and the specific design of a fuel tank venting system will depend on the size and type of the tank, as well as the intended use of the vehicle. In general, fuel tank vents are designed to allow air to flow in and out of the tank as needed, to prevent the build-up of pressure or vacuum that can lead to explosions, ruptures, or spills. To ensure the safety of their vehicles, it is important for manufacturers to design and maintain fuel tank venting systems in accordance with relevant safety guidelines and regulations, such as the Australian Standard, AS1940 The storage and handling of flammable and combustible liquids (AS1940).

Filtered vs Unfiltered tank vents

Filtered fuel tank vents and unfiltered fuel tank vents are different types of vents that are designed to meet different needs.

Unfiltered fuel tank vents are simple vents that allow air to flow in and out of the tank without any kind of filtration or screening. These vents are typically used in environments where the risk of contamination is low, or where the fuel being used is already treated to prevent contamination. Unfiltered vents are generally low maintenance and easy to install, making them a cost-effective option for many applications.

Filtered fuel tank vents, on the other hand, are designed to protect fuel systems from contamination by filtering out particles and other contaminants from the air that flows in and out of the tank. These vents may use a variety of filtration media, such as paper or foam, to capture particles and prevent them from entering the fuel system. Filtered vents are typically used in environments where the risk of contamination is high, such as in heavy equipment that operates in dusty or dirty conditions. The main benefit of filtered vents is that they can help to extend the service life of fuel filters and reduce the risk of equipment downtime due to blocked filters.

In general, the choice between filtered and unfiltered fuel tank vents will depend on the specific needs of the application and the level of protection required against contamination. It’s important to consider the operating environment and the potential risks of contamination when selecting a fuel tank vent.

Types of fuel tank vents

There are two main types of fuel tank vents: passive vents and active vents.

Passive

Passive vents are simple devices that allow air to flow in and out of the tank as needed, without the need for any external power source. These vents are typically located at the highest point of the tank and rely on the difference in atmospheric pressure to function. Passive vents are relatively low maintenance and are commonly used in small fuel tanks or in tanks that do not experience significant changes in temperature or pressure.

Passive fuel tank vents may use a variety of mechanisms to regulate the flow of air, such as a simple hole in the tank, a one-way valve, or a flapper valve. The specific design of the vent will depend on the size and type of the tank, as well as the intended use of the vehicle.

Active

Active vents, on the other hand, use a powered mechanism to control the flow of air in and out of the tank. These vents are often used in larger fuel tanks or in tanks that experience significant temperature or pressure changes. Active vents may be controlled by a pressure or temperature sensor, which activates the venting mechanism when a certain threshold is reached. Alternatively, active vents may be manually activated by the user, using a switch or other control.

There are several different types of active fuel tank vents, including mechanical vents, diaphragm vents, and pneumatic vents. Mechanical vents use a motor or other mechanical device to open and close a valve or flapper, regulating the flow of air into and out of the tank. Diaphragm vents use a flexible membrane to control the flow of air, while pneumatic vents use pressurized air to open and close a valve or flapper.

Active fuel tank vents offer more precise control over the venting process and can be customised to suit the specific needs of the vehicle. However, they may require more maintenance and may be more complex to install and repair compared to passive vents.

Remote Tank Breather

A remote tank breather is a type of fuel tank vent that is located remotely from the tank itself, rather than being directly attached to the tank. It can provide several benefits in terms of safety, performance, and convenience, making it an appealing option for many fuel system applications. It is generally accepted that having a properly designed and maintained fuel tank venting system, including a remote tank breather if appropriate, can help to prevent accidents and improve the overall safety of a vehicle.

Fuel tank explosions and ruptures can be serious hazards, and proper venting is an important safety feature that can help to prevent these types of incidents. By allowing pressure to be released from the tank and preventing the build-up of vacuum, fuel tank vents can help to prevent explosions, ruptures, and spills. A remote tank breather can provide additional benefits by separating the breather from the tank, reducing the risk of fire or explosion in the event of a fuel leak. A few of the benefits to using a remote tank breather include:

Improved air circulation

By locating the breather away from the tank, it is easier to ensure good air circulation around the tank, which can help to prevent the build-up of heat or pressure that can lead to explosions or ruptures.

Enhanced safety

By separating the breather from the tank, there is less risk of fire or explosion in the event of a fuel spill or leak. This can help to improve the overall safety of the vehicle and its occupants.

Increased flexibility

A remote tank breather can be in a more convenient or easily accessible location, making it easier to service or repair if necessary.

Enhanced fuel system performance

A remote tank breather can help to improve the performance of the fuel system by reducing the risk of contamination and ensuring a consistent flow of air into and out of the tank.

Venting Fuel Tanks

Fuel tank vents are an essential safety feature that helps to prevent the dangers associated with unvented tanks. By allowing pressure to be released and maintaining a certain level of vacuum, fuel tank vents help to prevent explosions, ruptures, and spills. Whether passive or active, fuel tank vents play a crucial role in ensuring the safety of vehicles and their passengers.

Banlaw’s diesel fuel tank vent system is designed to prevent spills and leaks by sealing the tank when it is full. The vent mechanism is also able to manage flow rates to match the refuelling system’s shut-off level. When the tank is full, a small amount of pressure is released through the vent, allowing the tank to return to atmospheric pressure quickly. Banlaw’s vents come in three variations: unfiltered, filtered, and fine-filtered. There is also an option for a remote tank breather. The filtered tank vent is particularly useful for protecting diesel fuel systems in heavy equipment that operate in dusty environments. This vent comes with a serviceable air filter that prevents particles from entering the tank and fuel system, extending the service life of OEM fuel filters, and reducing the risk of equipment downtime due to blocked filters.

Mark Fretwell

Mark is a mechanical engineer with over 11 years of experience in the hydrocarbon transfer industry. Currently, he works as a Mechanical Design Engineer for Banlaw, where he specialises in the implementation of Banlaw products and systems onto diesel-powered locomotives. Prior to his current role, Mark worked as a Sales Engineer, where he served as a Business Development Manager across NSW, VIC, TAS, and New Zealand. He worked directly with Banlaw’s distributor network and end customers, acting as a liaison between the Banlaw engineering team and customers on key R&D projects. He is always eager to share his knowledge and experience and is available for inquiries regarding diesel locomotive refueling systems, fuel management systems, or depot refueling infrastructure.

Safe container for flammable fluids, e.g., for a vehicle or oil heater

A fuel tank (also called a petrol tank or gas tank) is a safe container for flammable fluids, often gasoline or diesel fuel. Though any storage tank for fuel may be so called, the term is typically applied to part of an engine system in which the fuel is stored and propelled (fuel pump) or released (pressurized gas) into an engine. Fuel tanks range in size and complexity from the small plastic tank of a butane lighter to the multi-chambered cryogenic Space Shuttle external tank.

The fuel tanks for B-25 bombers Fill caps on a BMW automobile for hydrogen (left) and for gasoline (right) fuel tanks

Uses

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Typically, a fuel tank must allow or provide the following:

• Storage of fuel: the system must contain a given quantity of fuel and must avoid leakage and limit evaporative emissions.
• Filling: the fuel tank must be filled in a secure way, without sparks.
• Provide a method for determining level of fuel in tank, gauging (the remaining quantity of fuel in the tank must be measured or evaluated).
• Venting (if over-pressure is not allowed, the fuel vapors must be managed through valves).
• Feeding of the engine (through a pump).
• Anticipate potentials for damage and provide safe survival potential.

Plastic (high-density polyethylene HDPE) as a fuel tank material of construction, while functionally viable in the short term, has a long term potential to become saturated as fuels such as diesel and gasoline permeate the HDPE material.

Considering the inertia and kinetic energy of fuel in a plastic tank being transported by a vehicle, environmental stress cracking is a definite potential. The flammability of fuel makes stress cracking a possible cause of catastrophic failure. Emergencies aside, HDPE plastic is suitable for short term storage of diesel and gasoline. In the U.S., Underwriters Laboratories approved (UL 142) tanks would be a minimum design consideration.

Fuel tank construction

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Fuel tank for the Apollo Lunar Module, 1960s

While most tanks are manufactured, some fuel tanks are still fabricated by metal craftsmen or hand-made in the case of bladder-style tanks. These include custom and restoration tanks for automotive, aircraft, motorcycles, boats and even tractors. Construction of fuel tanks follows a series of specific steps. The craftsman generally creates a mockup to determine the accurate size and shape of the tank, usually out of foam board. Next, design issues that affect the structure of the tank are addressed - such as where the outlet, drain, fluid level indicator, seams, and baffles go. Then the craftsmen must determine the thickness, temper and alloy of the sheet he will use to make the tank. After the sheet is cut to the shapes needed, various pieces are bent to create the basic shell and/or ends and baffles for the tank. Many fuel tanks' baffles (particularly in aircraft and racecars) contain lightening holes. These flanged holes serve two purposes, they reduce the weight of the tank while adding strength to the baffles. Toward the end of construction, openings are added for the filler neck, fuel pickup, drain, and fuel-level sending unit. Sometimes these holes are created on the flat shell, other times they are added at the end of the fabrication process. Baffles and ends can be riveted into place. The heads of the rivets are frequently brazed or soldered to prevent tank leaks. Ends can then be hemmed in and soldered, or flanged and brazed (and/or sealed with an epoxy-type sealant) or the ends can be flanged and then welded. Once the soldering, brazing or welding is complete, the fuel tank is leak-tested.[1]

In the aerospace industry, the use of Fuel Tank Sealants is a common application for high temperature integral fuel tanks. This provides excellent resistance to fluids such as water, alcohols, synthetic oils and petroleum-based hydraulic fluids.[2]

Automotive fuel tanks

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Metal fuel tank for a 1996 Opel Blazer Fuel cell for a 1998-2001 Porsche GT3 Cup racing car

Passenger vehicles

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A larger fuel-tank results in a greater range for the car between refills, however the weight and space requirements of a larger tank are undesirable, especially in smaller cars. The average fuel tank capacity for cars is 50–60 L (12–16 US gal).[3]

The most common materials for fuel tanks are metal or plastic. Metal (steel or aluminium) fuel tanks are usually built by welding stamped sheetmetal parts together. Plastic fuel tanks usually built using blow molding, which allows more complex shapes to be used.

Some vehicles include a smaller reserve tank to be used when the main fuel tank is empty. Some other vehicles, typically 4WD vehicles, have a large secondary tank (or "sub-tank") to increase the range of the vehicle.

Racing fuel cell

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A racing fuel cell has a rigid outer shell and flexible inner lining to minimize the potential for punctures in the event of a collision or other mishap resulting in serious damage to the vehicle. It is filled with an open-cell foam core to prevent explosion of vapor in the empty portion of the tank and to minimize sloshing of fuel during competition that may unbalance the vehicle or cause inadequate fuel delivery to the motor (fuel starvation).[4]

Aircraft

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Layout of a modern airliner's main fuel tanks Two ways an aircraft's engine may receive fuel—the gravity-feed system, where no fuel pump is required other than a primer, and the fuel-pump system.

Aircraft typically use three types of fuel tanks: integral, rigid removable, and bladder.

• Integral tanks are areas inside the aircraft structure that have been sealed to allow fuel storage. An example of this type is the "wet wing" commonly used in larger aircraft. Since these tanks are part of the aircraft structure, they cannot be removed for service or inspection. Inspection panels must be provided to allow internal inspection, repair, and overall servicing of the tank. Most large transport aircraft use this system, storing fuel in the wings, belly, and sometimes tail of the airplane.
• Rigid removable tanks are installed in a compartment designed to accommodate the tank. They are typically of metal construction, and may be removed for inspection, replacement, or repair. The aircraft does not rely on the tank for structural integrity. These tanks are commonly found in smaller general aviation aircraft, such as the Cessna 172.
• Bladder tanks, or fuel cells,[5] are reinforced rubberized bags installed in a section of aircraft structure designed to accommodate the weight of the fuel. The bladder is rolled up and installed into the compartment through the fuel filler neck or access panel, and is secured by means of metal buttons or snaps inside the compartment. Many high-performance light aircraft, helicopters and some smaller turboprops use bladder tanks. One major down-side to this type of tank is the tendency for materials to work harden through extensive use making them brittle causing cracks.[

  citation needed

  ] One major plus side is the ability to use as much of the aircraft as possible to store fuel.
• Combat aircraft and helicopters generally use self-sealing fuel tanks.

Fuel tanks have been implicated in aviation disasters, being the cause of the accident or worsening it (fuel tank explosion).[6][failed verification] For example:

• The official "probable cause" for the explosion and subsequent crash of TWA Flight 800 is that an explosive fuel/air mixture existed in one of the aircraft's fuel tanks. Faulty wiring then provided an ignition source within the tank, destroying the airliner. While the accuracy of the official findings is still questioned in this case, similar explosions have occurred in other aircraft. It is possible to reduce the chance of fuel tank explosions by a fuel tank inerting system or fire-fighting foam in the tanks.[7]
• Burning fuel can explode or set fire to the same airplane or adjacent objects and people. In the 1960 Munich Convair 340 crash, a transport crashed into a major street. Burning fuel set fire to a tramcar. All 20 people aboard the plane and 32 passengers of the tram died.[8]

In some areas, an aircraft's fuel tank is also referred to as an aircraft fuel cell.

Water supply

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Water supply systems can have primary or backup power supplied by diesel-fueled generators fed by a small "day tank" and a much larger bulk storage fuel tank.[9][10]

Safety

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Proper design and construction of a fuel tank play a major role in the safety of the system of which the tank is a part. In most cases intact fuel tanks are very safe, as the tank is full of fuel vapour/air mixture that is well above the flammability limits, and thus cannot burn even if an ignition source were present (which is rare).

Bunded oil tanks are used for safely storing domestic heating oil and other hazardous materials. Bunding is often required by insurance companies, rather than single skinned oil storage tanks.

Several systems, such as BattleJacket and rubber bladders, have been developed and deployed for use in protecting (from explosion caused by enemy fire) the fuel tanks of military vehicles in conflict zones.[11]

For stationary fuel tanks, an economical way to protect them from hazards like extremes of temperature and vehicle crashes is to bury them. However, buried tanks are difficult to monitor for leaks. This has led to concern about environmental hazards of underground storage tanks.

See also

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References

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