Regan Brown
Running a return line to a fuel cell is a complex process that requires careful consideration of various factors. The return line is responsible for returning unused fuel from the carburetor or injection back to the fuel cell or tank. One crucial aspect is determining the optimal location for the return line, which can vary depending on the setup. Some run the return line to the bottom of the fuel cell, while others opt for the top. The size of the return line is also important, as an inadequate size can lead to aeration and pump issues. Additionally, the use of tubes, hoses, and valves in the return line can impact its performance and should be carefully selected. Safety considerations, such as limiting static electricity buildup and vapour levels, are also essential when designing the return line setup.
| Characteristics | Values |
|---|---|
| Return line fitting | On the left of the fuel cell |
| Return line length | 18 inches |
| Return line size | Should be large enough to prevent aeration |
| Return line material | Stainless steel hard line |
| Return line position | Should be kept below the fuel surface |
| Return line function | Returns unused fuel from the carb to the tank |
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What You'll Learn
The return line should be stainless hard line, not braided rubber hose
When running a return line back to the tank or fuel cell, it is important to consider the type of material used for the line. While braided rubber hoses are commonly used, they may not be the best choice for this application.
Braided rubber hoses are known to be sensitive to heat, water, and chemicals, which can lead to leaks or bursts. In the context of a fuel cell, the exposure to fuel and varying temperatures can accelerate the degradation of the rubber material. As a result, the use of braided rubber hoses may increase the risk of fuel leaks and potential safety hazards.
On the other hand, stainless hard lines offer several advantages over braided rubber hoses in this application. Stainless steel is known for its durability and resistance to corrosion. It is less susceptible to the damaging effects of fuel and temperature fluctuations, making it a safer option for fuel cell return lines.
Additionally, stainless hard lines provide better structural integrity than braided rubber hoses. They are less likely to kink or collapse, ensuring uninterrupted fuel flow and reducing the chances of aeration in the fuel cell. By maintaining a consistent fuel flow and minimizing aeration, the stainless hard line helps optimize the performance and efficiency of the fuel cell.
While the initial cost of stainless hard lines may be higher compared to braided rubber hoses, their longevity and reliability make them a more cost-effective solution in the long run. With proper maintenance and inspection, stainless hard lines can provide a safe and reliable solution for fuel cell return lines, reducing the risk of leaks and potential hazards associated with fuel systems.
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Return line location impacts pressure and aeration
The location of the return line in a fuel tank can impact pressure and aeration. The return line facilitates the return of fuel from the injectors back to the fuel tank. This line provides nearly constant pressure to the injectors, irrespective of their demand. A mechanical valve in the fuel rail regulates this pressure. If the pressure is too high, the valve allows more flow to escape, reducing the pressure, and if it is too low, the valve restricts the flow, increasing the pressure. Any fuel released from the valve passes through the return line.
The return line's location can influence pressure changes and aeration in the fuel tank. Running the return line from the top to the bottom of the tank, with the bottom of the tube a small distance from the tank bottom, can help reduce aeration and evaporation of fuel. This setup prevents the fuel from splashing and aerating, which can occur if the return line dumps above the fuel level. The slots cut into the tube also help eliminate pressure changes caused by fuel level variations or sloshing.
The size of the return line can also impact aeration. A sufficiently large return line is less likely to aerate the fuel. Additionally, ensuring that the return bung is located far away from the pickup can help eliminate aeration. The use of foam in smaller cells can also assist in reducing aeration.
The type of pump and the presence of a surge tank can also influence aeration. A small pump is less likely to cause aeration issues, while a high-performance pump can introduce aeration, especially in a system without foam. Running the return line into a surge tank that feeds the fuel pump can help prevent aeration, as the tank remains "full" and does not slosh unless the main tank's fuel level drops significantly.
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Return line size is important
The size of the return line is important when running a return line back to the fuel tank or fuel cell. The return line should be large enough to prevent aeration of the fuel. If the return line is too small, fuel pressure can creep up at idle or become erratic. This can lead to issues such as over-fuelling, as the fuel cannot return fast enough, and unstable pressure.
For example, one user with a Prostar 500 pump has a #10 main feed and a #10 return line, with a #8 on the vent at the tank. They also ensure they have a dip tube in the return fitting to prevent bubbles from forming as the fuel returns to the tank, which can cause issues with fuel injection. Another user with a similar setup has a #12 feeding pump, #10 to the fuel filter, and #10 from the fuel filter to the regulator, but they do not specify the size of their return line.
The size of the return line can also depend on the type of engine. For instance, EFI (electronic fuel injection) setups can run a smaller return line than carb setups because EFI requires more base pressure. However, the return line must still be large enough, usually one size smaller than the feed. For example, a -8 feed line would use a -6 return line. On the other hand, a carb setup requires the feed and return lines to be the same size.
Additionally, the size of the return line can depend on the pump being used. For instance, a user with a Weldon 2025 pump found that a -6 return line was sufficient, but when they upgraded to a "real" pump, they had to increase the size of the return line to -8. Similarly, another user with a Weldon 2035 pump uses a -6 return line, but they note that a -8 return line is recommended for practically all Weldon pumps.
In summary, the size of the return line is important to ensure proper fuel flow and pressure regulation. The return line should be sized appropriately to prevent issues such as aeration, erratic pressure, and over-fuelling. The specific size required can depend on various factors, including the type of engine, the pump being used, and the size of the feed line.
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Return line routing is important
However, it is important to note that returning fuel to the bottom of a large-capacity tank can also create problems. As the gas exerts significant pressure, at approximately 240 psi for a 30-gallon fuel cell, this pressure can burn out the fuel pump if it is equal to or less than the pressure on the fuel return line. Therefore, it is crucial to consider the capacity of the tank and the output of the fuel pump when determining the routing of the return line.
Additionally, the size of the return line plays a role in aeration. As long as the return line is large enough, aeration will not occur. The same principle can be observed when pouring water into a bucket with a hose. Blocking half of the hose with your finger will result in a significant difference in the flow. Similarly, the use of foam within the fuel cell can help reduce aeration, particularly in smaller cells.
The material of the return line should also be considered. While stainless steel hard lines are recommended for use inside the fuel cell, braided-covered rubber hoses should not be submerged in fuel. These factors contribute to the overall performance and longevity of the fuel cell setup.
In summary, return line routing is important as it directly impacts the functionality and longevity of the fuel cell and pump. By considering factors such as aeration, tank capacity, return line size, and material, one can ensure optimal performance and prevent issues such as fuel pump burnout.
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A one-way valve may not prevent back pressure
Fuel cells require specific operating pressures to function optimally. Back pressure control is applied to ensure that the pressure on the exhaust side of the fuel cell is kept within a desired range. This consistency in operating conditions helps in accurate and repeatable testing, ensuring reliable and comparable test results.
When running a return line to a fuel cell, it is important to consider the location of the return bung. The return bung should be located as far away from the pickup as possible to eliminate aeration. As long as the return line is large enough, it will not aerate the fuel. Additionally, if you are using a small cell, it should always be kept near full, while foam can help with larger cells.
The return pressure will vary slightly as the level of fuel changes in the cell. This will not matter if you have a large tank, but if you have a very small cell and a fuel-pressure-sensitive setup, it can cause some variation. Most N/A guys won't see any issues as long as they are running large enough lines. Large tanks also have fewer issues with "bubbles", as the extra volume acts like a plenum, smoothing out turbulence in the intake.
It is important to maintain a consistent back pressure in fuel cell testing, even in the presence of changes in flow rates, ambient conditions, or other system variables. This stability ensures that the fuel cell testing remains reliable and consistent throughout the entire duration. The back pressure regulator should provide high accuracy and precision in maintaining the desired back pressure, ensuring the fuel cell operates at the intended pressure levels.
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Frequently asked questions
The return line is responsible for returning unused fuel from the carb to the tank.
The return line should be located at the top of the fuel cell, with a hose inside that goes to the bottom of the tank.
The return line should be large enough to prevent aeration. If the return line is too small, it can cause issues with the fuel pump.
It is recommended to use a stainless hard line for the return line. Braided-covered rubber hoses should not be submerged in fuel.
