Regan Brown
Installing a return line in a fuel tank is a complex process that requires careful consideration. The placement of the return line, either at the top or bottom of the tank, is a key decision that can impact the fuel's aeration levels and the pump's workload. While some sources suggest returning fuel to the bottom of the tank to minimise aeration, others argue for returning above the fuel level to prevent the pump from working harder. Additionally, factors such as tank size, the use of tubes or hoses, and the type of line material must be taken into account to ensure a successful installation.
How to install a return line in a fuel tank
| Characteristics | Values |
|---|---|
| Return line placement | There is no consensus on whether the return line should be placed at the top or bottom of the fuel tank. Some sources claim that placing the return line at the bottom of the tank can cause aeration and affect fuel pressure, while others argue that returning fuel to the bottom of the tank reduces aeration. |
| Materials | Stainless steel or copper lines are recommended for the return line. Braided-covered rubber hoses should not be submerged in fuel. |
| Installation process | To install a return line, a hole must be drilled into the fuel tank, and a threaded bung can be added without welding. The bung is then collapsed and pressed against the inside of the tank by rotating a bolt with a wrench. |
| Aeration | Aeration can occur regardless of return line placement. However, ensuring the return line is large enough can minimise aeration. Returning fuel to the bottom of the tank and keeping the return bung away from the pickup can also help reduce aeration. |
| Fuel pressure | Returning fuel to the bottom of the tank may affect fuel pressure as the load on the pump changes with fuel level and consumption. |
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What You'll Learn
The placement of the return line
One school of thought suggests that the return line should discharge into the top of the fuel tank, in the free air space. This configuration is based on the assumption that it reduces the workload on the pump. By returning fuel to the top, the pump doesn't have to push the fuel back down into the tank, which could happen if the return line is at the bottom. Additionally, with the return line at the top, any air or bubbles in the fuel have a chance to disperse. However, this approach assumes that aeration is not a significant issue and that the fuel level in the tank doesn't fluctuate much, which may not always be the case.
On the other hand, some people argue that the return line should extend to the bottom of the tank or, at the very least, below the fuel surface. This setup is designed to minimize aeration by ensuring that the fuel is returned directly to the tank without the risk of air bubbles forming. This method is particularly important for smaller tanks or setups that are sensitive to fuel pressure changes. By returning the fuel to the bottom, you also avoid the potential issue of aerated fuel being sucked back into the pump inlet, which could affect performance.
It's worth noting that the size of the tank and the type of setup can influence the decision. Larger tanks tend to have fewer issues with aeration and bubbles due to their increased volume, which acts as a plenum, smoothing out turbulence. Additionally, the use of foam inserts in larger tanks can further reduce these issues. However, with smaller tanks, especially those with fuel pressure-sensitive setups, returning fuel to the bottom can help prevent fluctuations in return pressure as the fuel level changes.
Ultimately, the decision on the placement of the return line may depend on the specific vehicle, the size of the fuel tank, and the preferences of the installer. While there are valid arguments for both top and bottom return line placements, it's crucial to prioritize eliminating aeration and maintaining stable fuel pressure to ensure optimal performance and the longevity of the pump.
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The material of the return line
One popular option is to use a steel or copper line. These materials are known for their durability and corrosion resistance, making them suitable for long-term use in fuel tanks. Steel, in particular, is strong and resistant to damage, ensuring a long-lasting return line. Copper, on the other hand, has excellent thermal conductivity, which can help with heat dissipation in the fuel system.
Another option is to use a braided stainless hose. This type of hose is flexible and can be easier to route through the fuel tank during installation. However, it is important to note that submerging a braided-covered rubber hose in fuel is not recommended. If you plan to use a braided hose, it should be a stainless hard line to ensure compatibility with the fuel.
Aluminum is also a common material used for fuel tank return lines. Aluminum is lightweight, durable, and resistant to corrosion. Bevinsee, for example, offers a 6AN Universal Fuel Tank Return Line Fitting Bung Kit made of aluminum. This kit includes a threaded bung that allows for easy installation without the need for welding. The anodized aluminum construction provides rust resistance, ensuring a long-lasting and reliable return line.
The size of the return line is also a factor to consider. A larger return line can help reduce aeration by providing a smoother flow for the fuel. Additionally, ensuring that the return bung is located away from the pickup can further help in eliminating aeration.
In summary, the material of the return line depends on various factors, including durability, compatibility with fuel, ease of installation, and resistance to corrosion and rust. Steel, copper, stainless steel, and aluminum are all viable options, each offering unique advantages. It is important to carefully consider the specific requirements of your fuel tank and select the material that best meets those needs.
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Drilling a hole for the return line
First and foremost, it is essential to exercise extreme caution when drilling into a fuel tank to avoid any accidental sparks that could lead to a dangerous situation. Ensure you are wearing appropriate personal protective equipment, including eye protection and gloves, and that the work area is well-ventilated.
The drilling process itself is relatively straightforward. You will need to determine the exact location for the return line, taking into account factors such as the size of the tank, the presence of any existing fittings, and the desired path of the return line. Mark the spot on the tank where you plan to drill the hole, ensuring it is free from any obstructions. Choose a drill bit that is the correct size, typically a 1/2-inch drill bit, as specified by some manufacturers of return line kits.
It is crucial to use the right type of drill bit suitable for drilling through the material of your fuel tank, which is usually made of metal. Slowly and carefully drill through the marked spot, applying gentle but firm pressure to create a clean hole. Take your time during this process to avoid any slipping or mistakes that could damage the tank.
Once the hole is drilled, it is essential to deburr and smoothen the edges to prevent any damage to the return line and ensure a proper seal. You can use a metal file or sandpaper to carefully remove any sharp edges or burrs that may have formed during drilling. After creating a smooth hole, you can proceed with installing the return line, following the instructions provided with your chosen return line kit.
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The size of the return line
The primary function of a fuel return line is to ensure that fuel is returned to the tank, and the size of the line can impact the efficiency and effectiveness of this process. A larger return line can accommodate a higher volume of fuel flow, which is particularly important for high-performance engines or vehicles with large fuel tanks.
On the other hand, a smaller return line may be adequate for smaller engines or vehicles with lower fuel consumption. It's important to note that the size of the return line should be proportional to the size of the fuel tank and the engine's fuel requirements.
In addition to the diameter or cross-sectional area of the return line, the length of the line can also be a factor. If the return line is too long, it may create unnecessary restrictions on the fuel flow, affecting the overall performance of the fuel system.
When determining the size of the return line, it's crucial to consider the material and construction of the line as well. Stainless steel or aluminium are commonly used materials for fuel return lines, and the wall thickness and overall rigidity of the line can impact the flow characteristics.
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Preventing aeration
To prevent aeration, it is recommended that the return line is installed at the bottom of the fuel tank. This way, the fuel is returned below the fuel surface, reducing the chance of air being introduced into the fuel. Returning fuel to the bottom of the tank also helps to minimise the aeration and evaporation of fuel, without causing pressure changes due to fuel level fluctuations or sloshing.
However, it is important to note that returning fuel to the bottom of the tank can increase the risk of aerated fuel being sucked back into the pump inlet. To mitigate this, it is recommended to keep the return line as far away from the pickup line as possible. Additionally, ensuring that the return line is large enough can also help to prevent aeration, as it allows the fuel to flow back into the tank more smoothly.
Another factor to consider is the use of a tube or hose within the fuel tank. A tube can be used to direct the return line to the bottom of the tank, reducing the free fall of fuel and minimising aeration. However, it is important to ensure that the tube is securely connected to the return line and positioned correctly within the tank.
In some cases, it may not be possible to return the fuel to the bottom of the tank. In these instances, it is recommended to return the fuel as far away from the pickup line as possible and to use a bulkhead fitting on the top of the tank. While this may not completely eliminate aeration, it can help to reduce the amount of air introduced into the fuel.
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Frequently asked questions
There are varying opinions on this. Some sources suggest that the return line should be placed at the top of the tank, in free air space, to prevent aeration. However, others argue that returning fuel to the bottom of the tank can reduce aeration.
Aeration can cause air bubbles to form in the fuel, which can be sucked back into the pump inlet and affect the performance of the fuel system.
Stainless steel or copper lines are recommended for a return line inside a fuel tank. Braided-covered rubber hoses should not be submerged in fuel.
To install a return line, you will need to drill a 1/2" hole in the fuel tank and secure a threaded bung using a bolt and wrench. This will allow you to add the return line to the fuel tank.
Ensure that the return line is large enough to prevent aeration. The return line should also be located away from the pickup to eliminate aeration.
