Thoughts On Fuel Pump Cavitation

ask a barber if you need a haircut............

I think its more about the restriction than cavitation. I've seen that little rubber piece blown clean off a fuel return line numerous times with higher flow pumps.

A normal restriction won't cause the fpr pressure to jump, because the restriction amount stays the same. That rubber tip has a little slit in it that is supposed to help with drain back through the return back to the pump. The force of fuel opens and closes that flap causing the fpr pressure to bounce.

The small line causes the pressure to go up. The nipple causes it to bounce.

Cavitations causes issues....but why not make the return li e go to a different area inside the tank ? Its still circulating hot fuel. Thats why Ford made the return short. When fuel level is low the return sprays out of that tip dropping fuel temperature before it hits the rest of the fuel in the tank. It helps disperse some of the heat.

I'm no engineer....and could be wrong....but it sounds smart in my head.

That's my .02....not worth very much.

It can happen,95 hat 340 pump,less then half a tank I had issues.
Extending the return (not as easy as it looks) helped.
Had no choice but to use a hood mounted f/p gauge to keep an
eye on things. Note I am regulated to 7 psi and returning a lot of
fuel. A pump change and I can hold a steady 7 down below a 1/4 tank.

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.