Understanding Fuel Pressure: Tank Performance And Optimization

Fuel pressure refers to the pressure of the fuel vapours in a fuel tank. This pressure is important as it can indicate whether there is a leak in the tank. If there is too much pressure, it can be dangerous and cause the tank to rupture. If there is not enough pressure, it can cause engine performance issues. Fuel pressure is affected by factors such as temperature and altitude. To test fuel pressure, a gauge is used to measure the pressure in the tank. This can help identify any issues with the tank or fuel system.

How to pressure test a fuel tank

This guide will take you through the process of pressure testing a boat fuel tank.

Step 1: Acquire the Necessary Tools and Prepare the Tank

Get a pair of hose pinch pliers, an inflatable pipe plug, and a low-pressure air pressure gauge that can be tee-ed into a 3/8" fuel hose with a Schrader valve. You may be able to find these tools at your local hardware store.

Locate the fuel fill hose, the vent hose access ports, and the fuel pick-up access. Ensure that you have access to the fuel tank components, which can sometimes be tricky. Most boats have access ports for the fill and vent part (toward the front of the tank) and the pick-up tubes and sender section (at the back or aft of the tank).

Step 2: Install the Inflatable Pipe Plug and Pinch Off the Vent Hose

Install the inflatable pipe plug into the fuel fill port and pump it up to shut off the fuel fill hose. Use the hose pinch pliers to pinch off the fuel tank vent hose, ensuring that no air can escape.

Step 3: Remove the Fuel Hose and Install the Pressure Gauge

Remove the fuel hose from the pickup tube fitting. Install the low-pressure air pressure gauge and hose.

Step 4: Pump Air into the Tank

Pump air into the tank, but do not exceed 3 lbs of pressure (3 psi). Understand that too much air can damage the tank. Generally, you will want to stay around 2-3 psi.

Step 5: Locate a Leak, If There Is One

If the pressure gauge goes down, locate the leak. Spray the sender and all fittings and ports on the tank with soapy water and look for air bubbles. Most of the time, if there is a leak, it is the fuel sender or the fittings at the pick-up tubes. Ensure that the vent and fill hose are plugged off properly and that your pressure testing tool is not leaking.

Additional Information

If you are experiencing a fuel smell in your boat, you may need to pressure test your fuel tank to identify any leaks. It is important to note that this guide specifically addresses boat fuel tanks, and the process may vary for different vehicles or fuel tank types.

Releasing pressure from a fuel tank

Step 1: Remove the Circuit Relay

Firstly, locate the CIRCUIT RELAY in one of the plastic fuse boxes near the battery. It should be labelled as such. By removing this relay, you will interrupt the electrical circuit that controls the fuel pump, causing the engine to stall and the fuel pressure to decrease.

Step 2: Turn Off the Ignition Switch

Once the engine has stalled due to the previous step, turn off the ignition switch. This ensures that the fuel pump is not accidentally reactivated during the procedure, which could lead to a buildup of pressure again.

Step 3: Install the Circuit Opening Relay

At this point, you can install the circuit opening relay. This is a safety measure to ensure that the fuel pump remains inactive while you work on the fuel system.

Step 4: Remove the Gas Cap

Now, you can proceed to remove the gas cap to depressurise the fuel tank. It is important to use a rag or a protective cloth to cover the opening, as there may still be some residual pressure that could cause fuel spray. This step allows the built-up pressure to escape, reducing the risk of fuel spray when disconnecting fuel lines or performing other maintenance tasks.

Step 5: Disconnect Fuel Lines (Optional)

If you are performing maintenance that involves disconnecting fuel lines, it is important to use extreme caution. Even after releasing the pressure, some fuel may still be present in the lines. Place a rag or container underneath the connection to catch any spilled fuel. Slowly loosen the clamp or fitting, being prepared for potential fuel spray. Always wear safety glasses and protective clothing to shield your eyes and skin from fuel spray.

Step 6: Prime the Fuel System (After Releasing Pressure)

After releasing the fuel pressure, it is important to prime the fuel system to prevent excessive engine cranking during the next startup. Connect a jumper wire between the diagnosis connector terminals F/P (fuel pump) and GND (ground). Turn the ignition switch on for about 10 seconds to activate the fuel pump and check for fuel leaks. Finally, turn off the ignition switch and remove the jumper wire.

Safety Precautions:

It is important to treat fuel and fuel pressure with caution. Always work in a well-ventilated area and avoid open flames or sparks. Ensure that you are wearing appropriate protective gear, including eye protection, gloves, and clothing that covers your skin. If you are working on a diesel engine, exercise even more caution due to the extremely high pressures involved.

PSI levels in fuel tanks

Fuel pressure is the pressure at which fuel is pumped into a fuel tank. The PSI (pounds per square inch) levels in fuel tanks vary depending on the type of fuel tank and the vehicle.

For example, a standard 20-pound propane tank at 70 degrees Fahrenheit will have an internal pressure of 145 PSI. The same tank on a 100-degree day will have a pressure of 172 PSI. Propane pressure levels exceeding 200 PSI are likely to trigger a release from the safety relief valve commonly installed on propane storage tanks.

In the context of residential oil tanks, the manufacturer typically tests them at the factory to a pressure of 5 to 7 PSI. During the filling of a heating oil tank, the pressure is expected to be less than 5 PSI if the tank is adequately vented. However, if the venting is totally blocked or missing, pressures up to 280 PSI can occur.

For carburated car engines, the fuel pressure is usually around 4 to 7 PSI, while modern multipoint fuel-injected, high-performance engines may run at about 60 PSI. Modified cars with port injection typically operate at about 1900 PSI, while those with direct injection can reach upwards of 2000 PSI.

It is important to note that excessive pressure in fuel tanks can lead to leaks and even tank rupture, so maintaining appropriate PSI levels is crucial for safety and the proper functioning of the fuel system.

Fuel tank safety

Structural and Regulatory Compliance

Firstly, it is crucial to ensure that the fuel tank complies with structural integrity standards. The Environmental Protection Agency (EPA) mandates regular testing of above-ground tanks, also known as "bulk storage tanks." This involves a combination of visual inspections and scientific methods such as radiographic, ultrasonic, or hydrostatic testing.

State-Specific Regulations

Above-ground tanks are typically regulated by individual states. Some states may require the tank and its attachments to be painted specific colours to indicate their purpose. Additionally, certain states may mandate the installation of alarms on these tanks. It is essential to refer to the specific EPA guidelines for your state.

Annual Reviews and Staff Training

As a facility owner or manager, conducting annual reviews on fuel tank safety and cleanup procedures is of utmost importance. These reviews should be mandatory for all on-site staff, and they should include re-evaluations of their ability to handle fuel leaks, spills, and tank explosions. Annual reviews also provide an opportunity to introduce new safety protocols.

Staff training is another critical aspect of fuel tank safety. All personnel should be well-versed in inspecting, powering on and off the tank, and spill containment and cleanup measures.

Tank Design and Installation

When choosing a fuel tank, consider the size and space of your facility, as well as your fuel requirements. Above-ground tanks are generally easier to install, inspect, and maintain. They are also less expensive to set up. However, they are exposed to the elements and pose a higher risk of ignition in the event of an explosion or wildfire.

On the other hand, below-ground tanks are protected from the elements and above-ground disasters. They also free up above-ground space. However, they are more challenging to install due to excavation requirements and are more difficult to inspect and relocate.

Safety Requirements and Best Practices

• Ensure the tank has a proper support structure, including features like a structural foundation and adequate storage and pressure capacity.
• Monitor the tank for signs of corrosion and contamination during inspections.
• Never fill the tank to its full capacity. Leave room for fluid expansion due to temperature changes to prevent pressure build-up.
• If you have an indoor tank, use it only for indoor machinery to avoid a cumbersome and potentially dangerous setup.
• Flammable-liquid tanks must be fire-guarded to withstand surrounding fires for at least two hours.
• Outdoor above-ground tanks should be Underwriters Listed (UL) to indicate their purpose clearly.
• The containment area for spills should be at least 125% of the tank's size for maximum safety.
• Double-walled tanks provide enhanced safety by containing leaks and protecting the inner tank from external factors like rain and punctures.
• Install barriers and protective measures around the tank, such as piping, concrete pillars, wheel stops, or pipe bollards.
• Ensure proper lighting around the tank for easier detection of leaks at night.
• Check local fire fuel regulations and guidelines from the EPA and your local Department of Natural Resources (DNR).

Additional Considerations

Some other important considerations for fuel tank safety include:

• Visible labels on the tank indicating contents, hazards, storage capacity, and tank ID number.
• "No Smoking" signs posted near the tank in multiple languages.
• Regular monthly inspections for leaks, corrosion, and other damage, with documentation kept for at least three years.
• Maintain a minimum separation distance of three feet between flammable storage tanks.
• Keep a safe distance of at least 25 feet between the tank and any nearby buildings.

By adhering to these guidelines and regulations, you can help ensure the safe operation and maintenance of fuel tanks, mitigating risks such as fires, explosions, pollution, and theft.

Fuel tank leaks

If you suspect a fuel tank leak, it is important to take your vehicle to a mechanic as soon as possible. Driving with a leaking fuel tank is unsafe as it increases the risk of fire. Gasoline is highly flammable, and it can take just a small spark or a discarded cigarette to set it off.

Most fuel tank leaks can be repaired with minimal effort. Before attempting any repairs, you must access the tank, find the source of the leak, and clean the area around it. Small leaks can be patched up with epoxy putty, while larger leaks may require welding the leak shut. Welding requires draining the tank and ensuring it is free of fumes to avoid a fire hazard.

If your vehicle's fuel tank is damaged or leaking, it is important to take it to a professional mechanic for repair or replacement.

Frequently asked questions