The Evolution Of Pressure: Rubber Fuel Hose Explained

Rubber fuel hoses are a popular choice for many fuel systems due to their low cost and ease of installation. However, they have a limited lifespan and need to be periodically inspected and replaced. The quality of rubber hoses varies, and it is important to select a hose that can handle the required fuel pressure and has low permeability to prevent fuel loss and deterioration. Fuel injection hoses are designed to handle higher air pressure than regular fuel lines and must be able to withstand at least 50 PSI. The materials used for fuel injection hoses, such as synthetic rubber and PTFE, are resistant to fuel types and have a higher temperature resistance than regular rubber fuel lines.

Pressure rating

The pressure rating of a rubber fuel hose is an important characteristic to consider when selecting the right hose for your needs. The pressure rating indicates the maximum amount of pressure that the hose can safely withstand.

For carbureted engines, the typical maximum fuel pressure is relatively low, often just a few pounds per square inch (psi) inside the fuel line. In this case, a rubber hose with a lower pressure rating, such as those rated for 50 psi or less, would be sufficient. These low-pressure hoses are commonly used for applications such as lawn mower engine repairs and older carbureted engines.

However, for fuel-injected engines, the fuel pressure requirements are significantly higher, typically ranging from 50 psi to over 100 psi. Therefore, it is crucial to equip your vehicle with a hose that can reliably handle these higher pressure demands. Rubber fuel injection hoses are designed to meet these requirements and can generally withstand pressures of around 100 psi or more. Braided hoses, which are often made of materials like stainless steel, polyester, or nylon, can handle even higher pressures, with some capable of withstanding up to 350 psi.

It is important to note that the pressure rating of a hose is not always clearly labelled. In some cases, you may need to refer to industry standards or look up the specifications provided by the manufacturer. For example, hoses marked with SAE 30R9 are designed for high-pressure applications and can handle fuel injection systems with working pressures of 100 psi and above. On the other hand, hoses marked with SAE 30R6 and SAE 30R7 are considered low-pressure hoses and are not suitable for fuel injection systems.

When selecting a rubber fuel hose, it is crucial to consider not only the pressure rating but also other factors such as permeability, temperature rating, and compatibility with different types of fuel. By choosing a hose that meets the specific requirements of your application, you can ensure optimal performance, safety, and longevity.

Permeability

Rubber hoses have higher permeability compared to other materials, such as PTFE (polytetrafluoroethylene). This means that fuel can gradually escape through the walls of rubber hoses as vapour, which has negative economic and environmental implications.

To address this issue, modern rubber hoses have been designed with low permeability. However, cheaper options, such as lawn-mower-grade hoses, still have high permeability and will require more frequent replacement.

When selecting a rubber fuel hose, it is essential to consider the permeability specifications to ensure the hose meets the required standards and to minimise the negative impacts associated with high permeability.

Standards organisations, such as SAE (Society of Automotive Engineers) in the US and DIN (Deutsches Institut für Normung) in Europe, have developed standards and markings to indicate the permeability of rubber hoses. For example, the SAE 30R6 and SAE 30R7 standards indicate high permeability and a shorter lifespan, while modern hoses with low permeability are formulated to meet higher standards.

SAE standards

In the context of rubber fuel hoses, SAE standards become particularly important for ensuring safety, performance, and compatibility with different fuels. SAE J30 is the standard specifically related to fuel and oil hoses, including those used in internal combustion engines in mobile, stationary, and marine applications.

The SAE J30 standard covers a range of hoses with different pressure ratings and compatibility:

• SAE 30R2: Coupled and Uncoupled Synthetic Rubber Tube and Cover
• SAE 30R3: Lightweight Braided Reinforced Lacquer, Cement, or Rubber-Covered Hose
• SAE 30R5: Wire Inserted Synthetic Rubber Tube and Cover
• SAE 30R6, SAE 30R7, and SAE 30R8: Low-Pressure Coupled and Uncoupled Synthetic Rubber Tube and Cover
• SAE 30R9: Medium-Pressure Fuel Injection Hose
• SAE 30R10: In-Tank, Low-Pressure, Uncoupled Fuel Hoses
• SAE 30R11: Low Permeation Fuel Fill and Vent Hose
• SAE 30R12: Low Permeation Fuel Feed and Return Hose

These standards are crucial for ensuring the safe and reliable operation of fuel systems. They help prevent premature failure, burst lines, fuel leaks, and fuel contamination, which can lead to blocked fuel filters and injectors. By choosing the correct SAE-standard hose, you can ensure compatibility with different fuels, such as gasoline, diesel, biodiesel, or ethanol blends, and meet the required pressure ratings for your specific application.

Hose construction

The construction of a rubber fuel hose is a complex process that involves multiple layers of materials, each serving a specific function. Here is a detailed breakdown of the typical construction of a rubber fuel hose:

• Inner Layer: The inner layer, also known as the tube, is constructed from premium materials like Nitrile (NBR) or synthetic rubber. This layer comes into direct contact with the fuel and plays a crucial role in ensuring fuel compatibility and resistance to hydrocarbon permeation. Nitrile is commonly used due to its ability to withstand constant exposure to fuel without breaking down.
• Middle Layer: Encompassing the inner layer is a reinforcing spiral wrap, typically made of textile materials like nylon or a spiral weave. This layer adds mechanical strength to the hose, enabling it to withstand high operating pressures. It also provides structural support and helps maintain the shape of the hose.
• Outer Cover: The outermost layer, often made from materials like Chlorinated Polyethylene (CPE) or Neoprene (CR), serves multiple purposes. It provides temperature protection, abrasion resistance, and reduces construction costs. Additionally, this layer offers protection against external elements and helps extend the lifespan of the hose.

It is important to note that different types of rubber fuel hoses may have variations in their construction. For example, some hoses might have a single layer of nylon, while others might incorporate stainless steel or polyester braiding. The specific construction depends on the intended application and the required performance characteristics.

When selecting a rubber fuel hose, it is essential to consider factors such as pressure rating, permeability, compatibility with fuel types, temperature range, and flexibility. These factors will determine the suitability of the hose for a particular application and ensure its reliable performance.

Hose compatibility

When selecting a rubber fuel hose, it is crucial to ensure compatibility with the specific application and fuel type. The wrong choice can lead to premature failure, resulting in burst lines, fuel leaks, and contamination.

Fuel Type Compatibility

The standard definition of automotive fuel includes unleaded fuel (up to 98 octane) and diesel. Standard fuel hoses are typically not compatible with ethanol blends, biodiesel, or methanol. However, some suppliers offer EFI (Electronic Fuel Injection) fuel hoses that are compatible with a wider range of fuel types, including gasoline, diesel, biodiesel, E-85, methanol, and ethanol fuels.

Operating Pressure

The operating pressure of a fuel hose is an important consideration. Carbureted engines typically have maximum fuel pressures of a few psi, while fuel-injected engines require much higher pressures, often 50 psi or more. It is essential to choose a hose that can reliably handle the fuel pressure demands of the specific application.

Hose Standards and Markings

To help identify the compatibility and performance characteristics of a rubber fuel hose, industry standards, such as SAE J30 in the US and DIN 73379 in Europe, have created a numbering system for rubber hose standards. These standards specify pressure ratings, permeability, compatible fuels, and other characteristics for each hose type.

When purchasing a rubber fuel hose, look for markings or part numbers on the hose that indicate compliance with these standards. For example, hose types such as SAE 30R9 and SAE 30R7 indicate high-pressure and low-pressure hoses, respectively. It is recommended to avoid SAE 30R6 and SAE 30R7 hoses due to their high permeability and resultant short life.

Hose Construction and Materials

The construction and materials of a rubber fuel hose also play a role in its compatibility. Here are some common types:

• Nitrile Rubber Hose: This is the most common type, typically constructed with a premium inner layer made from NBR (Nitrile), a reinforcing spiral wrap, and an outer cover. Nitrile provides hydrocarbon permeation resistance and does not readily break down when in constant contact with fuel. The outer cover, often made from CR (Neoprene), provides temperature protection, abrasion resistance, and reduces cost.
• Nylon Tube: Nylon hose is the fuel hose of choice for many manufacturers due to its ability to reduce evaporative emissions to very low levels. It also offers a smooth internal surface and the ability to conform to different shapes, making installation quick and easy. However, nylon hose requires special tools for replacement and is more difficult to work with due to its rigid construction.
• Braided Hose: Braided hose is available in both nitrile and PTFE (Teflon) inner cores, with stainless, polyester, or nylon braiding. Nitrile braided hose has similar properties to EFI hose, while PTFE braided hose is lightweight, easy to assemble, and compatible with all fuels and oils. It also has excellent pressure and burst resistance, making it a good choice for performance applications.
• Push Lock Hose: Push lock hose is another type of nitrile hose with simple and secure fittings. However, some people have reported failures with this type of hose and connections.
• Submersible Fuel Hose: This type of hose is designed for constant contact with fuel, both internally and externally. It is constructed with an external flouroelaster tube cover, an aramid fibre spiral wrap, and a nitrile inner layer. It has good flexibility and is suitable for EFI systems.

Other Considerations

When selecting a rubber fuel hose, it is also important to consider factors such as temperature range, flexibility, durability, and cost. Additionally, ensure that the hose has a conductive chemical additive to allow for the safe discharge of static electricity generated by fuel flow.

Frequently asked questions