The problem:
In the event of a collision the inertia switch is supposed to open circuit, depriving the fuel pump of power. This shuts off fuel flow that might feed a fire.
The rubber duck bill is simply a one way check valve when the car turns over in the event of a collision. It keeps the fuel from flowing out of the return line, thus preventing fuel from being added to any fire that started as the result of the collision. A secondary effect is that the returning fuel helps to cool the pump as it sprays over it.
The video is correct in that returned fuel sprays out the duck bill check valve in an aerated, fan shaped stream. As shown in the video, that is indeed a problem in a car modified with a high performance engine. Replacing the duck bill check valve with a piece of metal tubing that runs to the bottom of the tank solves that problem. However, it has introduced another problem: If the car turns over onto the passenger side as the result of the collision, there is nothing shown or described to prevent the flow out of the return line. Simply put, there is no check valve in this system.This presents a fire hazard and could possibly feed a fire that was the result of the collision.
The beauty of the rubber duck bill check valve is that it is inexpensive, reasonably reliable, has no moving parts and creates no measurable restriction when used with a stock engine and pump. All the external check valves that I have seen have a two piece housing that screws together, a spring and a check ball. The spring insures that the check ball seals against reverse flow in any mounting position. However, it has at least five problems:
1.) it is prone to wear and decreased sealing efficiency,
2.) It has a flow restriction at higher flow rates,
3.) It may fail to work if dirt or corrosion get between the ball check valve and the seat.
4.) The spring may fail or get weak and not develop sufficient pressure to keep the check ball seated.
5. You would never know that it was defective until it failed to work in the event of a collision where the car turned over and a fire started. Not good at all...
Ford understood the limitations of this type of fuel return system and engineered a returnless system in later models of high performance Mustangs. The computer has a sensor that measures the fuel pressure and increases and decreases the fuel pressure as needed.
Stuck with what we have got:
The only thing that I can come up with is a baffle that mounts just below the rubber duck bill check valve that directs the returned fuel to the area outside the baffle that surrounds the pump inlet. To perfect that option, you would need a test rig like the one shown in the video.
